TWI873083B - A catalyst and a process for the production of ethylenically unsaturated carboxylic acids or esters - Google Patents

Abstract

A catalyst has a modified silica support and comprises a modifier metal, zirconium and/or hafnium, and a catalytic metal on the modified support. The catalyst has at least a proportion, typically, at least 25%, of modifier metal present in moieties having a total of up to 2 modifier metal atoms. The moieties may be derived from a monomeric and/or dimeric cation source. A method of production: - provides a silica support with isolated silanol groups with optional treatment to provide isolated silanol groups (-SiOH) at a level of <2.5 groups per nm²; contacting the optionally treated silica support with a monomeric zirconium or hafnium modifier metal compound to effect adsorption onto the support; optionally calcining the modified support for a time and temperature sufficient to convert the monomeric zirconium or hafnium compound adsorbed on the surface to an oxide or hydroxide of zirconium or hafnium in preparation for catalyst impregnation.

Description

Catalyst and method for producing ethylene unsaturated carboxylic acid or ester

The present invention relates to a modified silica catalyst carrier, a catalyst incorporating a modified silica carrier and a method for producing ethylenically unsaturated carboxylic acids or esters, especially α,β unsaturated carboxylic acids or esters, more especially acrylic acids or esters, such as (alkyl)acrylic acids or (alkyl)acrylic acid alkyl esters, especially (meth)acrylic acids or (meth)acrylic acid alkyl esters, such as methacrylic acid (MA) and methyl methacrylate (MMA), by condensing the carboxylic acids or esters with formaldehyde or a source thereof, such as dimethoxymethane, in the presence of such catalysts, especially by condensing propionic acid or its alkyl esters, such as methyl propionate, with formaldehyde or a source thereof in the presence of such modified silica carrier catalytic metal catalysts. The present invention is therefore particularly relevant to the production of methacrylic acid (MAA) and methyl methacrylate (MMA).

As mentioned above, the unsaturated acids or esters can be prepared by the reaction of carboxylic acids or esters and suitable carboxylic acids or esters are alkanoic acids (or esters) of the formula ^R3 - _CH2 - ^COOR4 , wherein ^R3 and ^R4 are each independently a suitable substituent known in the art of acrylic acid compounds, such as hydrogen or an alkyl group, especially a lower alkyl group containing, for example, 1 to 4 carbon atoms. Thus, for example, methacrylic acid or its alkyl esters, especially methyl methacrylate, can be prepared by the catalytic reaction of propionic acid or the corresponding alkyl ester (e.g. methyl propionate) with formaldehyde as a methylene source according to reaction sequence 1.

R ³ -CH ₂ -COOR ⁴ +HCHO------->R ³ -CH(CH ₂ OH)-COOR ⁴

and

R ³ -CH(CH ₂ OH)-COOR ⁴ ------->R ³ -C(：CH ₂ )-COOR ⁴ +H ₂ O

Sequence 1

An example of reaction sequence 1 is reaction sequence 2

CH ₃ -CH ₂ -COOR ⁴ +HCHO------->CH ₃ -CH(CH ₂ OH)-COOR ⁴ n

CH ₃ -CH(CH ₂ OH)-COOR ⁴ ------->CH ₃ -C(:CH ₂ )-COOR ⁴ +H ₂ O

Sequence 2

The above reaction sequence is typically carried out at high temperature, usually in the range of 250-400°C, using an acid/base catalyst. In the case where the desired product is an ester, the reaction is typically carried out in the presence of the relevant alcohol in order to minimize the formation of the corresponding acid by ester hydrolysis. In addition, for convenience, it is often necessary to introduce formaldehyde in the form of a complex of formaldehyde and methanol. Therefore, for the production of methyl methacrylate, the reaction mixture fed to the catalyst will generally consist of methyl propionate, methanol, formaldehyde and water.

The known method for producing MMA is to use formaldehyde to catalytically convert methyl propionate (MEP) into MMA. The known catalyst used for this is a cesium catalyst incorporated into a carrier such as silicon dioxide.

WO1999/52628 discloses a catalyst for producing α,β unsaturated carboxylic acids or esters by condensing propionic acid or the corresponding alkyl esters, wherein the catalyst comprises alkali metal-doped silicon dioxide impregnated with at least one modifier element, wherein the modifier element is selected from the group consisting of boron, aluminum, magnesium, zirconium and bismuth, preferably zirconium and/or aluminum and/or boron, and the alkali metal is selected from potassium, bismuth or caesium, preferably caesium.

WO2003/026795 discloses a catalyst for aldol condensation (including the production of α,β unsaturated carboxylic acids by condensing propionic acid or propionic acid esters), olefin polymerization, dehydration, hydroxylation and isomerization, wherein the catalyst comprises a silica-metal hydrogel impregnated with a catalytic metal, wherein the metal of the hydrogel is selected from the group consisting of zirconium, titanium, aluminum and iron, preferably zirconium, and the catalytic metal is selected from the group consisting of alkali metals and alkaline earth metals, preferably cesium.

The inventors have now discovered that catalysts comprising certain metal-modified silica supports and containing catalytic metals provide high levels of selectivity in the condensation of methylene sources such as formaldehyde and carboxylic acids or alkyl esters such as methyl propionate when at least a certain proportion of the modifier metal is incorporated into or present in a support in the form of a metal species having a total of up to two zirconium and/or bismuth atoms.

It is known from Yung-Jin Hu et al., J.Am.Chem.Soc. Vol. 135, 2013, p. 14240 that zirconium can form large clusters in solution. Zr-18 clusters are typical.

However, the inventors have surprisingly discovered that when the modified silica support contains zirconia and/or bismuth oxide moieties derived from monomeric and/or dimeric modifier metal cation sources (such as compounds thereof) at the beginning of the modification, rather than such larger clusters, an improvement in the binding of the catalytic metal to the modified support and a subsequent higher selectivity for the production of unsaturated carboxylic acids or esters by condensation of the corresponding acids or esters with a methylene source (such as formaldehyde) has been found. In addition, the inventors have discovered that the modified silica support that provides such high selectivity contains monomeric or dimeric modifier metal atoms after deposition/adsorption on the surface of the silica.

Still further, the inventors have discovered that when such modified silica supports are used, the catalyst surface sintering rate has been found to be retarded and the loss of surface area where catalytic reactions occur during the condensation reaction is reduced.

Therefore, catalysts comprising such modified silica supports and containing catalytic metals are remarkably effective catalysts for the production of α,β ethylenically unsaturated carboxylic acids or esters by condensation of the corresponding acids or esters with a methylene source such as formaldehyde, which offer several advantages such as high levels of selectivity and/or reduced sintering of the catalyst surface.

Therefore, according to a first aspect of the present invention, a catalyst is provided, which comprises a modified silica carrier, a modified silica carrier comprising a modifier metal; and a catalytic metal located on the modified silica carrier, wherein the modifier metal is selected from one or more of zirconium and/or arsenic, and is characterized in that at least a certain proportion, typically at least 25%, of the modifier metal is present in the form of a modifier metal portion having a total of at most 2 modifier metal atoms.

According to another aspect of the present invention, a catalyst is provided, which comprises a modified silica carrier, a modified silica carrier comprising a modifier metal; and a catalytic metal located on the modified silica carrier, wherein the modifier metal is selected from one or more of zirconium and/or arsenic, and is characterized in that at least a certain proportion, typically at least 25%, of the modifier metal is present in the form of a modifier metal portion derived from a monomeric and/or dimerized modifier metal cation source.

A monomeric and/or dimeric modifier metal is contacted with a silica support in solution as a source of monomeric and/or dimeric zirconium or ebonite modifier metal cations (such as a compound thereof) to adsorb the modifier metal on the support to form a modifier metal moiety. A suitable source may be a complex of the modifier metal in a dissolved state, more typically a ligand complex.

According to a second aspect of the present invention, a modified silica carrier for a catalyst is provided, comprising a silica carrier and a modifier metal, wherein the modifier metal is selected from one or more of zirconium and/or arsenic, and is characterized in that at least a certain proportion, typically at least 25%, of the modifier metal is present in the form of a modifier metal portion having a total of at most 2 modifier metal atoms.

According to a third aspect of the present invention, a modified silica carrier for a catalyst is provided, comprising a silica carrier and a modifier metal, wherein the modifier metal is selected from one or more of zirconium and/or arsenic, and is characterized in that at least a certain proportion, typically at least 25%, of the modifier metal is present in the form of a modifier metal portion derived from a monomeric and/or dimerized modifier metal cation source at the beginning of the modification.

The modified silica carrier herein is modified by a modifier metal. Typically, the modifier metal is an adsorbate adsorbed on the surface of the silica carrier. The adsorbate can be chemically adsorbed or physically adsorbed on the surface of the silica carrier, typically it is chemically adsorbed thereon. The modifier metal portion is generally a modifier metal oxide portion.

The silica carrier is generally in the form of a silica gel, more typically in the form of a xerogel or a hydrogel.

Typically, the modifier metal is adsorbed on the surface of the silica support. Thus, typically, the modifier metal is present as a metal oxide moiety on the surface of the modified silica gel support.

Alternatively, the modifier metal may be present in the carrier in the form of a co-gel. In such cases, the modified silica carrier is a silica-metal oxide gel, which typically contains zirconia and/or einsteinium oxide moieties.

Typically, the modifier metal is present in the modified silica support in an effective amount to reduce sintering and improve catalyst selectivity. Typically, at least 30%, such as at least 35%, more preferably at least 40%, such as at least 45%, most suitably at least 50 %, such as at least 55%, for example at least 60% or 65%, and most preferably at least 70%, such as at least 75% or 80%, more typically at least 85%, most typically at least 90%, especially at least 95% of the modifier metal in the modified silica support is in the form of a moiety with a total of 1 and/or 2 metal atoms, especially in the form of a moiety with a total of 1 metal atom or is derived from monomeric and/or dimeric metal compounds at such contents at the beginning of the formation of the modified silica.

For the avoidance of doubt, modifier metal moieties having a total of 1 metal atom are considered to be monomeric and modifier metal moieties having a total of 2 metal atoms are dimeric. In particularly preferred embodiments, at least 35%, more preferably at least 40%, such as at least 45%, most suitably at least 50 %, such as at least 55%, for example at least 60% or 65%, and most preferably at least 70%, such as at least 75% or 80%, more typically at least 85%, most typically at least 90%, especially at least 95% of the modifier metal is present as a monomeric metal moiety, or in any case is typically derived from a zirconium and/or bismuth compound having such levels of modifier metal as a monomeric compound at the start of modification. Generally speaking, the modifier metal moiety on silicon dioxide is a modifier metal oxide moiety.

Clusters of zirconium and/or arsenic larger than 2 metal atoms dispersed throughout a support such as a hydrogel support have been unexpectedly found to reduce the selectivity of the reaction to produce α,β ethylenically unsaturated carboxylic acids or esters by condensation of the corresponding acid or ester with a methylene source such as formaldehyde. It has also been unexpectedly found that such large clusters increase sintering of the modified silica particles relative to clusters of the modifier metal having 2 or 1 metal atoms, thereby reducing the surface area that reduces strength and reduces catalyst life before activity becomes unacceptably low. Additionally, selectivity is often lower depending on the nature of the modifier metal clusters.

Typically, the modifier metal is dispersed in a substantially homogeneous manner throughout the carrier.

Typically, the modified silica carrier is a xerogel. The gel can also be a hydrogel or an aerogel.

The gel may also be a silica-zirconia and/or silica-bezobium co-gel. The silica gel may be formed by any of a variety of techniques known to those skilled in the art of gel formation, such as those mentioned herein. Typically, the modified silica gel is prepared by a suitable adsorption reaction. A suitable technique is to adsorb a relevant metal compound (such as a zirconium and/or bezobium compound) onto a silica gel (such as a silica dry gel) to form a modified silica gel having a relevant modifier metal portion.

Methods for preparing silica gels are well known in the art and some of these methods are described in The Chemistry of Silica: Solubility, Polymerisation, Colloid and Surface Properties and Biochemistry of Silica, Ralph K Iler, ed., 1979, John Wiley and Sons Inc., ISBN 0-471-02404-X and references therein.

Methods for preparing silica-zirconia cogels are known in the art and some of these methods are described in US 5,069,816, Bosman et al., J Catalysis, Vol. 148 (1994), p. 660, and Monros et al., J Materials Science, Vol. 28, (1993), p. 5832.

Specific examples of the present invention will now be described with reference to the accompanying examples and drawings, in which: FIG1 shows an HRTEM image of Zr-modified silicon dioxide Example 5; FIG2 shows an HRTEM image of Zr-modified silicon dioxide Example 7; FIG3 shows an HRTEM image of Zr-modified silicon dioxide Example 14; FIG4 shows an HRTEM image of Zr-modified silicon dioxide Example 15; FIG5 shows an HRTEM image of Zr-modified silicon dioxide Example 17; and FIG6 shows an HRTEM image of Zr-modified silicon dioxide Example 18.

FIG. 7 shows the MMA+MAA selectivity (%) relative to catalyst activity for the catalysts prepared in Examples 20 to 74; FIG. 8 shows the catalyst selectivity for the mixed monomer/trimer catalysts prepared in Examples 75 to 79; and FIG. 9 shows the catalyst sintering constants as determined by the advanced aging test described in Example 81.

In preferred embodiments, the modified silica support is not formed by co-gelling, i.e., is not silica-zirconia, silica-bezoarsinia, or silica-zirconia/bezoarsinia formed by co-gelling, such as by mixing a sodium silicate solution with a modifier metal complex in a sulfuric acid solution.

In these embodiments, zirconium and/or einsteinium are typically incorporated as adsorbates on the surface of the silica support.

Preferably, the modified silica carrier catalyst and modified silica carrier according to any aspect of the present invention may be substantially free, essentially free, or completely free of fluorine. Fluorine may be present in trace amounts due to unavoidable environmental contamination. By "substantially free", we mean catalysts and carriers containing less than 1000 parts per million (ppm) of fluorine. By "substantially free" we mean catalysts and carriers containing less than about 100 ppm of fluorine and by "completely free" we mean catalysts containing less than 200 parts per billion (ppb) of fluorine.

Advantageously, when at least a portion of the modifier metal incorporated into the modified silica of the above aspects of the invention is derived from a source of monomeric and/or dimerized modifier metal cations at the beginning of the formation of the modified silica, it has been found that during the production of α,β ethylenically unsaturated carboxylic acids or esters, the reaction selectivity is increased and/or the sintering rate of the catalyst surface is reduced.

The metal and metal oxide components of the modified silicon dioxide carrier according to the present invention are related to zirconium and/or einsteinium and zirconium oxide and/or einsteinium oxide, rather than silicon dioxide.

Preferably, the content of the modifier metal present in the modified silica or catalyst may be up to 7.6× ^10-2 mol/mol silica, more preferably up to 5.9× ^10-2 mol/mol silica, and most preferably up to 3.5× ^10-2 mol/mol silica. Typically, the content of these metals is between 0.067× ^10-2 and 7.3× ^10-2 mol/mol silica, more preferably between 0.13× ^10-2 and 5.7× ^10-2 mol/mol silica, and most preferably between 0.2× ^10-2 and 3.5× ^10-2 mol/mol silica. Typically, the modifier metal is present in an amount of at least 0.1 x ^10-2 mol/mol silica, more preferably at least 0.15 x ^10-2 mol/mol silica and most preferably at least 0.25 x ^10-2 mol/mol silica.

Preferably, when zirconium is the modifier metal, the content of zirconium metal may be up to 10% w/w, more preferably up to 8% w/w, and most preferably up to 5.5% w/w of the modified silica carrier. Typically, the content of zirconium metal is between 0.1-10% w/w of the modified silica carrier, more preferably between 0.2-8% w/w and most preferably between 0.3-5% w/w. Typically, the content of zirconium metal is at least 0.5% w/w of the modified silica carrier, such as 0.8% w/w, more typically at least 1.0% w/w, and most typically at least 1.5% w/w.

Preferably, the content of cobium metal may be up to 20% w/w, more preferably up to 16% w/w, and most preferably up to 10% w/w of the modified silica carrier. Typically, the content of cobium metal is between 0.2-20% w/w of the modified silica carrier, more preferably between 0.4-16% w/w and most preferably between 0.6-10% w/w. Typically, the content of cobium metal is at least 1.0% w/w, more typically 2.0% w/w, and most typically at least 3.0% w/w of the modified silica carrier.

The silica component of the silica-zirconia carrier may typically form 86.5-99.9 wt % of the modified carrier, more typically 89.2-99.7 wt %, and most typically 93.2-99.6 wt %.

The silica component of the silica-arsenic oxide carrier typically forms 76.4-99.8 wt %, more typically 81.1-99.5 wt %, and most typically 88.2-99.3 wt % of the modified carrier.

By the term "up to 2 metal atoms" or the like as used herein is meant 1 and/or 2 metal atoms. Preferably, the modified silica support and catalyst according to any aspect of the present invention comprises a metal moiety, typically a metal oxide moiety having up to 2 metal atoms and optimally 1 metal atom. It is therefore understood that such moieties are monomeric or dimeric metal moieties.

Preferably, the catalytic metal may be one or more alkali metals. The catalytic metal is a metal other than zirconium or arsenic. Suitable alkali metals may be selected from potassium, arsenic and caesium, preferably arsenic and caesium. Caesium is the best catalytic metal.

Suitably, the catalytic metal such as cesium may be present in the catalyst in an amount of at least 1 mol/100 (silicon + metal (zirconia and/or arsenic)) mol, more preferably at least 1.5 mol/100 (silicon + metal) mol, and most preferably at least 2 mol/100 (silicon + metal) mol. The amount of the catalytic metal may be at most 10 mol/100 (silicon + metal) mol in the catalyst, more preferably at most 7.5 mol/100 (silicon + metal) mol, and most preferably at most 5 mol/100 (silicon + metal) mol in the catalyst.

Preferably, the content of the catalytic metal in the catalyst is in the range of 1-10 mol/100 (silicon + metal) mol, more preferably 2-8 mol/100 (silicon + metal) mol, and most preferably 2.5-6 mol/100 (silicon + metal) mol.

Unless otherwise indicated, the amount of alkali metal or alkali metal in the catalyst refers to the alkali metal ion and not the salt.

Alternatively, the catalyst may have a wt% of the catalytic metal in the catalyst in the range of 1 to 22 wt%, more preferably 4 to 18 wt%, most preferably 5-13 wt%. Such amounts would apply to all alkali metals, but particularly to cesium.

The catalyst may comprise any suitable weight ratio of catalytic base metal: zirconium and/or cobalt metal. Typically, however, the weight ratio of cesium:zirconium in the catalyst is in the range of 2:1 to 10:1, more preferably 2.5:1 to 9:1, and most preferably 3:1 to 8:1, the weight ratio of cesium:arbium in the catalyst is in the range of 1:1 to 5:1, more preferably 1.25:1 to 4.5:1, and most preferably 1.5:1 to 4:1, the weight ratio of zirconium:zirconium in the catalyst is in the range of 1.2:1 to 8:1, more preferably 1.5:1 to 6:1, and most preferably 2:1 to 5:1, and the weight ratio of zirconium:arbium in the catalyst is in the range of 0.6:1 to 4:1, more preferably 0.75:1 to 3:1, and most preferably 1:1 to 2.5:1. Thus, the catalytic metal:modifier metal molar ratio in the catalyst is typically at least 1.4 or 1.5:1, preferably it is in the range of 1.4 to 2.7:1, such as 1.5 to 2.1:1, especially 1.5 to 2.0:1, typically in this regard, the modifier metal is zirconium and the catalytic metal is cesium. Generally speaking, the amount of catalytic metal in this context exceeds the amount required to neutralize the modifier metal.

Preferably, the catalytic metal is present in the range of 0.5-7.0 mol/mol modifier metal, more preferably 1.0-6.0 mol/mol, and most preferably 1.5-5.0 mol/mol modifier metal.

Suitably, the catalytic metal may be incorporated into the modified silica support by any method known in the art, such as by impregnation, co-gelation or vapor deposition of the catalytic metal.

As used herein, the term "impregnation" includes adding a catalytic metal dissolved in a solvent to prepare a solution, adding the solution to a xerogel or an aerogel, and allowing the solution to be absorbed into the voids within the xerogel or the aerogel.

Typically, the catalyst of the present invention may be in any suitable form. A typical embodiment is in the form of discrete particles. Typically, in use, the catalyst is in the form of a fixed bed of catalyst. Alternatively, the catalyst may be in the form of a fluidized bed of catalyst. Another alternative is a monolithic reactor.

In the case of a fixed bed of catalyst, it is desirable to form the supported catalyst into particles, aggregates or shaped units (e.g., spheres, cylinders, rings, saddles, stars, multi-petals) prepared by granulation or extrusion, typically having maximum and minimum dimensions in the range of 1 to 10 mm, more preferably having an average dimension greater than 2 mm, such as greater than 2.5 or 3 mm. The catalyst is also effective in other forms, such as in the form of powders or small beads of the same size as indicated. In the case of using a catalyst in the form of a fluidized bed, it is desirable that the catalyst particles have maximum and minimum dimensions in the range of 10-500 gm, preferably 20-200 gm, and most preferably 20-100 gm.

The content of catalytic metals in the catalyst (in atoms/100 atoms (silicon + zirconium and/or euryl) or wt%) can be determined by appropriate sampling and averaging of the samples. Typically, 5-10 samples of a particular catalyst batch are obtained and the base metal content is determined and averaged, for example, by XRF, atomic absorption spectroscopy, neutron activation analysis, ion coupled plasma mass spectrometry (ICPMS) or ion coupled plasma atomic emission spectroscope (ICPAES).

The content of specific types of metal oxides in the catalyst/support is determined by XRF, atomic absorption spectroscopy, neutron activation analysis or ion coupled plasma mass spectrometry (ICPMS) analysis.

The typical average surface area of the modified silica supported catalyst according to any aspect of the present invention is in the range of 20-600 ^m2 /g, more preferably 30-450 ^m2 /g and most preferably 35-350 ^m2 /g, as measured by BET multipoint method using Micromeritics Tristar 3000 surface area and porosity analyzer. A reference material for checking the performance of the instrument can be carbon black powder (Part No. 00416833-00) supplied by Micromeritics with a surface area of 30.6 ^m2 /g (+/-0.75 ^m2 /g).

If the catalyst material is porous, it is typically a combination of mesopores and macropores with an average pore size between 2 and 1000 nm, more preferably between 3 and 500 nm, and most preferably between 5 and 250 nm. Macropore size (greater than 50 nm) can be determined by mercury infusion porosimetry using NIST standards, while mesopores (2-50 nm) are determined using the Barrett-Joyner-Halenda (BJH) analysis method using liquid nitrogen at 77 K. The average pore size is the void volume weighted average of the void volume relative to the pore size distribution.

The average pore volume of the catalyst particles may be less than 0.1 ^cm3 /g but is generally in the range of 0.1-5 ^cm3 /g as measured by uptake by a fluid such as water. However, microporous catalysts with very low porosity are not optimal as they may inhibit the migration of reagents through the catalyst and a more preferred average pore volume is between 0.2-2.0 ^cm3 /g. Pore volume may alternatively be measured by a combination of nitrogen adsorption and mercury intrusion porosimetry at 77K. Pore volume is measured using a Micromeritics TriStar surface area and porosity analyzer as in the case of surface area measurements and the same standards are employed.

In the present invention, it has been discovered that controlling the size of the modifier metal portions is unexpectedly beneficial. However, to obtain the maximum benefit, it is necessary to control the proximity of adjacent modifier metal portions, because the modifier metal portions may otherwise combine with each other and thus increase the size of the modifier metal portions.

Therefore, according to the fourth aspect of the present invention, a method for manufacturing a modified silica carrier is provided, which comprises the following steps: providing a silica carrier having a silanol group; contacting the silica carrier with a monomer and/or dimerized modifier metal compound, so that the modifier metal is adsorbed on the surface of the silica carrier by reacting with the silanol group.

Typically, the modifier metal is selected from zirconium or arsenic.

Preferably, the adsorbed modifier metal cations are sufficiently spaced apart from one another to substantially prevent their oligomerization, and more preferably they trimerize with adjacent modifier metal cations.

Typically, at least 25%, more typically at least 30%, such as at least 35%, more preferably at least 40%, such as at least 45%, most suitably at least 50 %, such as at least 55%, for example at least 60% or 65%, and most preferably at least 70%, such as at least 75% or 80%, more typically at least 85%, most typically at least 90%, especially at least 95% of the modifier metal contacting the silica support in the contacting step is a monomeric or dimeric modifier metal. Thus, at least 25%, more typically at least 30%, such as at least 35%, more preferably at least 40%, such as at least 45%, most suitably at least 50 %, such as at least 55%, for example at least 60% or 65%, and most preferably at least 70%, such as at least 75% or 80%, more typically at least 85%, most typically at least 90%, especially at least 95% of the modifier metal adsorbed on the silica support is present in the form of a modifier metal moiety having a total of at most 2 modifier metal atoms.

According to another aspect of the present invention, a method for manufacturing a modified silica carrier according to any of the aspects herein is provided, comprising the following steps: providing a silica carrier having a silanol group; treating the silica carrier with a monomer and/or a dimerized modifier metal compound so that the modifier metal is adsorbed on the surface of the silica carrier by reacting with the silanol group, wherein the adsorbed modifier metal atoms are sufficiently spaced apart from each other to substantially prevent oligomerization with adjacent modifier metal atoms, and more preferably are sufficiently spaced apart from each other to substantially prevent trimerization with adjacent modifier metal atoms.

Preferably, spacing of modifier metal atoms is achieved by: a) reducing the concentration of silanol groups on the silica support and/or b) attaching stabilizing ligands of sufficient size to the modifier metal prior to treating the silica support.

According to yet another aspect, a method for producing a catalyst is provided, comprising the following steps:- i. providing a silica carrier having isolated silanol groups and optionally treating the carrier to provide isolated silanol groups (-SiOH) at a content of <2.5 groups/nm2; ii. contacting the optionally treated silica carrier with a monomeric zirconium or bismuth modifier metal compound to adsorb the modifier metal on the carrier, typically adsorbing at least 25% of the modifier metal on the carrier; said separated silanol groups; iii. removing any solvent or liquid carrier of said modifier metal compounds as appropriate; iv. calcining said modified silicon dioxide for a time and temperature sufficient to convert said monomeric zirconium or bismuth compound adsorbed on the surface into an oxide or hydroxide of zirconium or bismuth; v. treating said calcined modified silicon dioxide with a catalytic base metal to impregnate said modified silicon dioxide with said catalytic metal to form said catalyst and calcining said catalyst as appropriate.

According to another aspect of the present invention, a method for manufacturing a modified silica carrier for a catalyst is provided, comprising the following steps: i. providing a silica carrier having isolated silanol groups and optionally treating the carrier to provide isolated silanol groups (-SiOH) with a content of <2.5 groups/nm2; ii. compounding the optionally treated silica carrier with a monomeric zirconium or ebonite modifier metal; iii. optionally, removing any solvent or liquid carrier for the modifier metal compounds; iv. optionally, calcining the modified carrier for a time and temperature sufficient to convert the monomeric zirconium or benzene compounds adsorbed on the surface to oxides or hydroxides of zirconium or benzene in preparation for catalyst impregnation.

Preferably, the concentration of silanol groups is reduced prior to treatment with a modifier metal compound by calcination, chemical dehydration or other suitable method.

Preferably, the modifier metal cation source in this article is a compound solution of the modifier metal, so that the compound is in a dissolved state when it contacts the carrier to be adsorbed on the carrier.

Typically, the solvent of the solution is not water.

Typically, the solvent is an aliphatic alcohol, typically selected from C ₁ -C ₆ alkanols such as methanol, ethanol, propanol, isopropanol, butanol, pentanol and hexanol, more typically methanol, ethanol or propanol.

Advantageously, the proximity of the adsorbed modifier metal to adjacent modifier metal cations can be controlled by the concentration of the modifier metal in the contacting step and by: - a) the concentration of silanol groups on the silica support and/or b) the size of any stabilizing ligands attached to the modifier metal cations.

The concentration of silanol groups on the silica support prior to adsorption is preferably controlled by calcination or other suitable methods known to those skilled in the art. Identification methods include, for example, LT Zhuravlev, in "Colloids and Surfaces: Physicochemical and Engineering Aspects, Vol. 173, pp. 1-38, 2000", which describes four different forms of silanols that can coexist on the surface of silica gels: isolated silanols, para-silanols, ortho-silanols, and internal silanols. These can be identified by infrared spectroscopy analysis as narrow absorption peaks at 3730-3750 cm ^-1 , while other silanols show broad peaks between 3460 and 3715 cm ^-1 (see "The Surface Properties of Silicas, Andre P Legrand, John Wiley and Sons, 1998 (ISBN 0-471-95332-6) pp. 147-234").

A stabilizing ligand is meant to be coordinated to the modifier metal and not removed by adsorption of the metal onto the silica surface. Thus, the stabilizing ligand is typically coordinated to the modifier metal in solution prior to treating the silica surface with the modifier metal. For the avoidance of doubt, the stabilizing ligand is typically removed by treatment of the silica surface after adsorption of the modifier metal.

The size of the stabilizing ligands can effectively space the modifier metals to prevent them from combining.

According to other aspects of the present invention, a method for manufacturing a catalyst or a modified silica carrier for one or more catalysts as described in the scope of the patent application is provided.

Suitable ligands herein may be stable ligands selected from molecules with unshared electron pairs containing oxygen or nitrogen atoms capable of forming a 5- or 6-membered ring with a zirconium or arsenic atom, as the case may be. Examples include diketones, diimines, diamines, diols, dicarboxylic acids or derivatives thereof, such as esters, or molecules having two different such functional groups and in either case with respective N or O atoms separated by 2 or 3 atoms to form a 5- or 6-membered ring. Examples include pentane-2,4-dione; esters of 3-oxobutyric acid and aliphatic alcohols containing 1 to 4 carbon atoms, such as ethyl 3-oxobutyrate, propyl 3-oxobutyrate, isopropyl 3-oxobutyrate, n-butyl 3-oxobutyrate, tert-butyl 3-oxobutyrate; heptane-3,5-dione; 2,2,6,6,-tetramethyl-3,5-heptanedione; 1,2-ethanediol; 1,2-propylene glycol; 1,3-propylene glycol; 1,3-butylene glycol; diols; 1,2-butanediol; 1,2-diaminoethane; ethanolamine; 1,2-diamine-1,1,2,2-tetracarboxylate; 2,3-dihydroxy-1,4-succinate; 2,4-dihydroxy-1,5-pentanedioate; salts of 1,2-dihydroxybenzene-3-5-disulfonate; diethylenetriaminepentaacetic acid; nitrilotriacetic acid; N-hydroxyethylethylenediaminetriacetic acid; N-hydroxyethylimidoacetic acid; N,N-dihydroxyethylglycine; oxalic acid and its salts. The most preferred are pentane-2,4-dione, heptane-3,5-dione, 2,2,6,6,-tetramethyl-3,5-heptanedione, 3-hydroxybutyric acid ethyl ester and 3-hydroxybutyric acid tert-butyl ester. Compared to larger ligands, smaller bidentate ligands having, for example, less than 10 carbon and/or heteroatoms in total are able to form small complexes, which can allow for higher concentration deposition on the surface of the silicon dioxide. Therefore, the modifier metal cation source herein can be in the form of a complex of zirconium and/or einsteinium with such smaller ligands, preferably with at least one of such ligands. Such compounds can include unstable ligands, such as solvent ligands (e.g., in alcohol solvents), alkoxide ligands, such as ethoxides or propoxides, etc.

The concentration of the better separated silanol groups determines the maximum number of sites where the modifier metal is adsorbed. By controlling this concentration, the proximity of the adsorbed modifier metal can be effectively determined, since the distribution of the silanol sites will generally be homogeneous. The silanol concentration used to make the modified silica support according to the present invention can be less than 2.5 groups/nm2, more typically less than 1.5 groups/nm2, and most typically less than 0.8 groups/nm2. The suitable range of silanol concentration for making modified silica carriers may be 0.1-2.5 silanol groups/square nanometer, more preferably 0.15-1.0 silanol groups/square nanometer, and most preferably 0.2-0.7 silanol groups/square nanometer.

Generally, the concentration of the modifier metal in the cationic form should be set at a level that prevents the formation of a large double layer on the support surface, which would result in metallic interactions of the modifier metal. In addition, filling of gaps in the initial monolayer should be avoided to prevent interactions with adjacent strongly adsorbed modifier metals, which could result in weak adsorption of modifier metals away from silanol sites. Typical concentration ranges for the modifier metals of the present invention can be as described herein.

Typically, at least 30%, such as at least 35%, more preferably at least 40%, such as at least 45%, most suitably at least 50% , such as at least 55%, for example at least 60% or 65%, and most preferably at least 70%, such as at least 75% or 80%, more typically at least 85%, most typically at least 90%, especially at least 95% of the modifier metal in the modifier metal compound is a dimeric and/or monomeric modifier metal compound, more typically monomeric, when its source is contacted with the support so that these compounds are adsorbed on the support.

According to another aspect of the present invention, a method for preparing a catalyst is provided, the catalyst comprising a modified silica carrier, a modified silica carrier comprising a modifier metal; and a catalytic metal on the modified silica carrier, wherein the modifier metal is selected from one or more of zirconium and/or arsenic, and is characterized in that at least a certain proportion, typically at least 25%, of the modifier metal is present in the form of a monomeric modifier metal portion, the method comprising the steps of: treating the silica carrier to provide a catalyst having a molar ratio of <2.5 groups/square nanometers; 100% of the isolated silanol groups (-SiOH) are present on the treated carrier; reacting the treated carrier with a monomeric zirconium or benzene monomeric modifier metal compound to achieve its bonding with at least 25% of the isolated silanol groups; removing any solvent or liquid carrier as appropriate; calcining the modified silicon dioxide for a time and temperature sufficient to convert the monomeric zirconium or benzene compounds adsorbed on the surface into oxides or hydroxides of zirconium or benzene; treating the calcined modified silicon dioxide with a catalytic base metal to impregnate the modified silicon dioxide with the catalytic metal.

Advantageously, by providing a smaller number of isolated silanol sites and by incorporating monomeric zirconium or bismuth species at these sites, a catalyst support is provided which results in increased catalyst selectivity, reduced sintering rate, and better catalyst aging.

A suitable method for treating silica to provide a specified content of separated silanol groups is calcination. However, other techniques, such as hydrothermal treatment or chemical dehydration are also possible. US5583085 teaches chemical dehydration of silica with dimethyl carbonate or ethyl dicarbonate in the presence of an amine base. US4357451 and US4308172 teach chlorination with _SOCl2 , followed by dechlorination with _H2 or ROH, followed by chemical dehydration with oxygen in a dry atmosphere. Chemical dehydration by heat treatment can provide up to 100% silanol removal for a minimum of 0.7/nm2. Therefore, in some examples, chemical dehydration can provide more scope for silanol group control.

The term isolated silanols (also called monosilanols) is well known in the art and these groups are distinguished from ortho or para or endo silanols. Suitable methods for determining the occurrence of isolated silanols include surface sensitive infrared spectroscopy and ¹ H NMR or ³¹ Si NMR.

According to the fifth aspect of the present invention, a method for manufacturing a catalyst according to any previous aspect of the present invention is provided, which comprises the following steps: forming modified silicon dioxide according to any of the previous aspects, and contacting the modified silicon dioxide carrier with a solution containing a catalytic metal to impregnate the modified silicon dioxide with the catalytic metal.

Preferably, the silica support is dried or calcined prior to treatment with the modifier metal cation source. The modified silica formed may be independent of whether the prior drying or calcination was performed prior to the addition of the catalytic metal.

The silica may be in the form of a gel before treatment with the modifier metal. The gel may be in the form of a hydrogel, xerogel or aerogel at the start of the modification.

The silica carrier may be a xerogel, a hydrogel or an aerogel. Preferably, the silica carrier is a xerogel.

The silica support may be treated with a metal cation source by any of a variety of techniques known to those skilled in the art of support formation. The silica support may be contacted with the metal cation source in such a manner that the modifier metal is dispersed throughout the silica support. Typically, the zirconium and/or eum may be homogeneously dispersed throughout the silica support. Preferably, the modifier metal is dispersed throughout the silica support by adsorption.

As used herein, the term "adsorption" or the like in connection with a modifier metal means the incorporation of the modifier metal onto the surface of the silica support, typically by chemical adsorption, through the interaction of a metal cation source with the silica support.

Typically, adding the modifier to the silica support involves the steps of adsorbing a metal cation source on the silica support to form an organometallic complex and calcining the complex to convert the organometallic complex to a metal oxide portion. Typically, the modifier metal is thus homogeneously dispersed throughout the silica support. Typically, zirconium and/or einsteinium are dispersed throughout the silica support.

Examples of suitable metal cation sources herein include organic complexes such as zirconium (pentane-2,4-dione) ₄ , zirconium (ethyl 3-oxobutyrate) ₄ , zirconium (heptane-3,5-dione) ₄ , zirconium (2,2,6,6-tetramethylheptane-3,5-dione) ₄ , zirconium (propoxide salt) (pentane-2-3-dione) ₃ , zirconium (propoxide salt) ₃ (2,2,6,6-tetramethyl-3,5-heptanedione) (zirconia (butyl) ₃ (tert-butyl 3-oxobutyrate), zirconium (Ot-butyl) ₂ (tert-butyl 3-oxobutyrate) ₂ and metal salts such as zirconium perchlorate, zirconium nitrate and zirconium oxychloride. Typically, the metal cation source is provided in the form of an organic complex.

Typically, the modifier metal is contacted with the silica carrier in solution. Preferably, the metal cation source is provided in any solvent in which the metal cation source is soluble. Examples of suitable solvents include water or alcohols. Preferred solvents are alcohols such as methanol, ethanol, propanol, isopropanol, butanol, pentanol, and hexanol.

Preferably, the metal cation source is added to the silicon dioxide in the alcohol solution in the form of a metal salt.

In one embodiment, the metal cation source is provided in one of methanol, ethanol, isopropanol, propanol, butanol, isobutanol or 2-butanol as a solution of one or more of the following: zirconium(IV) acetylacetonate (zirconia,tetrakis(2,4-pentanedione O,O')), zirconium(heptane-3,5-dione) ₄ , zirconium(2,2,6,6-tetramethyl-3,5-heptanedione) ₄ , zirconium(IV) ethyl 3-oxobutyrate, zirconium(IV) tert-butyl 3-oxobutyrate or zirconium(IV) isopropyl 3-oxobutyrate.

Preferably, after the modifier metal is adsorbed on the silica support, the solvent is removed by evaporation.

Optionally, the modified silica support is calcined to remove any ligands or other organics from the modified support.

A skilled person will appreciate that the catalytic metal may be added to the modified silica by any suitable means. Typically, to produce a modified silica catalyst, the modified silica is contacted with the catalytic metal.

Typically, to make the catalyst, the modified silica support is contacted with an acidic, neutral or alkaline aqueous solution containing the catalytic metal (such as cesium, in the form of a salt or base of the catalytic metal). Alternatively, the support may be contacted with a water-miscible solution of a catalytic metal salt in an organic solvent. Preferred solvents are alcohols such as methanol, ethanol, propanol and isopropanol, preferably methanol. The best solvent is methanol. Optimally, the catalytic metal is added as a salt solution in methanol. Low levels of water may be present in the solution, typically up to 20 vol%.

Typically, the conditions of temperature, contact time and pH during this stage of the catalyst production process allow the modified silica support to be impregnated with the catalytic metal to form a modified silica supported catalyst.

Typical conditions for the temperature of this step are between 5-95°C, more typically between 10-80°C and most typically between 20-70°C. The temperature of this step may be at least 5°C, more typically at least 10°C, most typically at least 20°C.

The typical contact time between the modified carrier and the solution containing the catalytic metal in this step may be between 0.05-48 hours, more typically between 0.1-24 hours, and most typically between 0.5-18 hours. The contact time may be at least 0.05 hours, more typically at least 0.1 hours, and most typically at least 0.5 hours.

The concentration of the catalytic metal salt solution in this step depends on a number of factors, including the solubility limit of the catalytic metal compound, the porosity of the modified silica carrier, the desired loading of the catalytic metal on the carrier and the method of addition, including the amount of liquid used to impregnate the carrier, the pH value and the choice of catalytic metal compound. The concentration in the solution is best determined experimentally.

Suitable salts of the catalytic metal used to catalyze the metal incorporation may generally be selected from one or more of the group consisting of formates, acetates, propionates, bicarbonates, chlorides, nitrates, hydroxides and carbonates, more typically hydroxides, acetates or carbonates and most typically hydroxides and/or carbonates. The pH may be controlled during the impregnation by adding ammonia and the metal compound or by using a suitable catalytic metal compound, such as formates, carbonates, acetates or hydroxides, more preferably hydroxides or carbonates, in all cases alone, in combination or together with a suitable carboxylic acid. It is most important to control the pH within a preferred range at the end of the impregnation to achieve satisfactory adsorption. Most typically, these salts may be incorporated using alkaline solutions of the salts. If the salts themselves are not alkaline, a suitable base such as ammonium hydroxide may be added. Since hydroxide salts are alkaline in nature, a mixture of one or more of the above salts with a hydroxide salt of a particular catalytic metal such as cesium may be suitably prepared.

The skilled person will appreciate that the catalytic metal of the present invention may be added to the modified silica support by any suitable means. After depositing the compound on the support using a suitable aqueous salt and subsequent drying of the surface-coated support as appropriate, the catalyst may be fixed to the support typically by calcination.

In general, drying of the modified silica support is achieved by suitable methods known to the skilled person, such as in a drying unit or an oven.

Typically, the catalyst contains between 0.01-25% w/w water, more typically 0.1-15% w/w water and most typically between 0.5 %-5.0 w/w water.

The modified silica-supported catalyst containing the catalytic metal may be dried or calcined as appropriate, the calcination process being well known to those skilled in the art.

In some cases it may be necessary to calcine the support formed from the reforming stage at 200-1000°C, more typically 300-800°C, most typically 350-600°C, prior to adding the catalytic metal. In a preferred calcination of the support formed from the reforming stage, the temperature is at least 375°C, such as 400°C or 450°C. The calcining atmosphere should typically contain some oxygen, suitably 1-30% oxygen and most suitably 2-20% oxygen to allow organic residues to be removed in the form of carbon dioxide and water. The calcination time may typically be between 0.01 and 100 hours, suitably 0.5-40 hours, most suitably 1-24 hours. The calcined support, such as a xerogel material, should be cooled to a suitable temperature for impregnation. The addition of the catalytically active metal may be carried out by the methods described for the uncalcined material or may be carried out by any other conventional method for impregnating catalyst supports, such as xerogel supports, such as using a solvent other than water, such as an alcohol, suitably methanol, ethanol, propanol or isopropanol or using a slightly wet impregnation method in which only enough solution is added to the xerogel support to fill the pores of the xerogel support. In this case, the concentration of the catalytically active metal may be calculated so as to introduce a target amount of the catalytically active metal into the xerogel support material rather than providing an excess of a lower concentration solution by the methods previously described. The addition of the catalytically active metal may utilize any preferred method known in the art. The calcination technique is particularly advantageous where an organic complex is used as the zirconium and/or bismuth source, as it may be necessary to modify the subsequent catalyst preparation process prior to impregnation with cesium to remove at least a portion of the organic complex salt. Advantageously, calcination of the modified support has been found to reduce the catalytic metal:modifier metal ratio and therefore the catalytic metal required. This is unexpected and provides another improvement of the present invention.

According to the sixth aspect of the present invention, a method for producing ethylenically unsaturated carboxylic acids or esters, typically α,β ethylenically unsaturated carboxylic acids or esters, is provided, which comprises the following steps: contacting formaldehyde or a suitable source thereof with a carboxylic acid or ester in the presence of a catalyst and optionally in the presence of an alcohol, wherein the catalyst is any one of the first aspect or other aspects of the present invention as defined herein.

Advantageously, catalysts comprising modified silica as defined herein and containing a catalytic metal have also been found to be remarkably effective catalysts for making α,β ethylenically unsaturated carboxylic acids or esters by condensation of the corresponding acid or ester with a methylene source such as formaldehyde, thereby having reduced catalyst surface sintering, improved selectivity and providing a high catalyst surface area. In particular, improved properties are found when monomeric and/or dimerized modifier metal moieties are used and/or when the modified silica support is calcined prior to treatment with the catalytic metal. In addition, the use of certain metal complexes to incorporate the modifier metal on the support by adsorption provides a suitable source of monomeric and/or dimerized modifier metal moieties. Such sources also allow control over the properties of the modifier metal and provide a more uniform distribution of the modifier metal fraction.

The term "a suitable source thereof" in relation to the formaldehyde of the fourth aspect of the present invention means that free formaldehyde can be formed in situ from the source under the reaction conditions or the source can act as an equivalent of free formaldehyde under the reaction conditions, for example, it can form the same reaction intermediate as formaldehyde so that an equivalent reaction occurs.

A suitable source of formaldehyde may be a compound of formula (I):

wherein R ⁵ and R ⁶ are independently selected from C ₁ -C ₁₂ hydrocarbon or H, X is O, n is an integer from 1 to 100, and m is 1.

Typically, ^R5 and ^R6 are independently selected from _C1 - _C12 alkyl, alkenyl or aryl as defined herein, or H, more suitably _C1 - _C10 alkyl or H, _{most suitably C1-C6 alkyl} or H, especially methyl or H. Typically, n is an integer from 1 to 10, more suitably 1 to 5, especially 1-3.

However, other sources of formaldehyde may be used, including trioxane.

Therefore, suitable sources of formaldehyde also include any equilibrium combination that can provide a source of formaldehyde. Examples of such equilibrium combinations include but are not limited to dimethoxymethane, trioxane, polyoxymethylene ^R1 -O-( _CH2 -O) _i - ^R2 (wherein ^R1 and/or ^R2 are alkyl or hydrogen, i=1 to 100), paraformaldehyde, formalin (formaldehyde, methanol, water) and other equilibrium combinations, such as a mixture of formaldehyde, methanol and methyl propionate.

The polyoxymethylene is a higher formaldehyde or hemiformaldehyde of formaldehyde and methanol, CH ₃ —O—(CH ₂ —O) _i —CH ₃ (“formaldehyde-i”) or CH ₃ —O—(CH ₂ —O) _r H (hemiformaldehyde-i), wherein i=1 to 100, suitably 1-5, especially 1-3, or other polyoxymethylenes having at least one non-methyl terminal group. Thus, the source of formaldehyde may also be a polyoxymethylene of the formula R ³¹ —O—(CH ₂ —O—) iR ³² , wherein R ³¹ and R ³² may be the same or different groups and at least one is selected from C ₁ -C ₁₀ alkyl, for example R ³¹ = isobutyl and R ³² = methyl.

Generally, suitable sources of formaldehyde are selected from dimethoxymethane, lower hemiformals of formaldehyde and methanol CH ₃ —O—(CH ₂ —O) _i —H (where i=1-3), formalin, or a mixture comprising formaldehyde, methanol, and methyl propionate.

Typically, the term formalin means a mixture of formaldehyde:methanol:water in the ratio of 25 to 65 wt %:0.01 to 25 wt %:25 to 70 wt %. More typically, the term formalin means a mixture of formaldehyde:methanol:water in the ratio of 30 to 60 wt %:0.03 to 20 wt %:35 to 60 wt %. Most typically, the term formalin means a mixture of formaldehyde:methanol:water in the ratio of 35 to 55 wt %:0.05 to 18 wt %:42 to 53 wt %.

Typically, the mixture comprising formaldehyde, methanol and methyl propionate contains less than 5% by weight of water. More suitably, the mixture comprising formaldehyde, methanol and methyl propionate contains less than 1% by weight of water. Most suitably, the mixture comprising formaldehyde, methanol and methyl propionate contains 0.1 to 0.5% by weight of water.

According to a seventh aspect of the present invention, there is provided a method for preparing an ethylenically unsaturated acid or ester, comprising reacting an alkanoic acid or ester of formula R ¹ -CH ₂ -COOR ³ with formaldehyde or a suitable source of formaldehyde of formula (I) as defined below:

wherein R5 is methyl and R6 is H; X is O; m is 1; and n is any value between 1 and 20 or any mixture thereof; in the presence of a catalyst according to any aspect of the present invention, and optionally in the presence of an alkanol; wherein R1 is hydrogen or an alkyl group having 1 to 12, more preferably 1 to 8, most preferably 1 to 4 carbon atoms and R3 may also independently be hydrogen or an alkyl group having 1 to 12, more preferably 1 to 8, most preferably 1 to 4 carbon atoms.

Thus, the inventors have discovered that having zirconium and/or arsenic in the form of a metal oxide moiety according to the invention can unexpectedly improve the selectivity for the condensation of a methylene source such as formaldehyde with a carboxylic acid or an alkyl ester such as methyl propionate to form an ethylenically unsaturated carboxylic acid. In addition, the sintering rate of the catalyst surface during the condensation reaction is significantly and unexpectedly reduced.

Thus, it has been found that the catalyst of the invention is particularly advantageous for a specific process, namely the condensation of formaldehyde and methyl propionate in the presence of methanol for the preparation of MMA.

In the case of making MMA, the catalyst is typically contacted with a mixture comprising formaldehyde, methanol and methyl propionate.

The method of the sixth or seventh aspect of the invention is particularly suitable for the preparation of acrylic acid and alkyl acrylic acid and its alkyl esters, and methylene-substituted lactones. Suitable methylene-substituted lactones include 2-methylene valerolactone and 2-methylene γ-butyrolactone, respectively, derived from valerolactone and γ-butyrolactone. Suitable (alkyl) acrylic acid and its esters are (C _0-8 alkyl) acrylic acid or (C _0-8 alkyl) acrylic acid alkyl esters, typically derived from the reaction of the corresponding alkanoic acid or ester with a methylene source (such as formaldehyde) in the presence of a catalyst, suitably methacrylic acid, acrylic acid, methyl methacrylate, ethyl acrylate or butyl acrylate, more suitably methacrylic acid or especially methyl methacrylate (MMA) derived from propionic acid or methyl propionate, respectively. Thus, in the production of methyl methacrylate or methacrylic acid, the preferred ester or acid of formula ^R1 - _CH2 - ^COOR3 is methyl propionate or propionic acid, respectively, and the preferred alkanol is therefore methanol. However, it will be appreciated that in the production of other ethylenically unsaturated acids or esters, the preferred alkanol or acid will be different.

The reaction of the present invention can be a batch or continuous reaction.

Typical conditions of temperature and gauge pressure in the method of the sixth or seventh aspect of the present invention are between 100°C and 400°C, preferably between 200°C and 375°C, and optimally between 275°C and 360°C; and/or between 0.001MPa and 1MPa, preferably between 0.03MPa and 0.5MPa, and optimally between 0.03MPa and 0.3MPa. The typical residence time of the reactants in the presence of a catalyst is between 0.1 and 300 seconds, preferably between 1-100 seconds, optimally between 2-50 seconds, and especially between 3-30 seconds.

The amount of catalyst used in the process of making the products of the present invention is not critical and will be determined by the practicality of the process employing the catalyst. However, the amount of catalyst will generally be selected to achieve the best selectivity and yield of the product and an acceptable temperature for operation. However, the skilled person will understand that the minimum amount of catalyst should be sufficient to cause effective catalyst surface contact of the reactants. In addition, the skilled person will understand that there is actually no upper limit to the amount of catalyst relative to the reactants but in practice this may be additionally controlled by the required contact time and/or economic considerations.

The relative amounts of the reagents in the methods of the sixth or seventh aspects of the invention may vary within wide limits but generally the molar ratio of formaldehyde or a suitable source thereof to the carboxylic acid or ester is in the range of 20:1 to 1:20, more preferably 5:1 to 1:15. The optimum ratio will depend on the formaldehyde form and the ability of the catalyst to release formaldehyde from the formaldehyde species. Thus, highly reactive formaldehyde species wherein one or both of R ³¹ and R ³² in R ³¹ O-(CH ₂ -O) _i R ³² are H require relatively low ratios, typically in this case the molar ratio of formaldehyde or a suitable source thereof to the carboxylic acid or ester is in the range of 1:1 to 1:9. In the case where both R ³¹ and R ³² are other than H, such as for example in CH ₃ O—CH ₂ —OCH ₃ or in trioxane, higher ratios are optimal, typically 6:1 to 1:3.

As mentioned above, water may also be present in the reaction mixture due to the formaldehyde source. Depending on the formaldehyde source, it may be necessary to remove some or all of the water therefrom prior to catalysis. Maintaining the water content below that in the formaldehyde source may be beneficial for catalytic efficiency and/or subsequent purification of the product. Less than 10 mol% water in the reactor is preferred, more preferably less than 5 mol%, most preferably less than 2 mol%.

The molar ratio of alcohol to acid or ester is typically in the range of 20:1 to 1:20, preferably 10:1 to 1:10, and most preferably 5:1 to 1:5, for example 1:1.5. However, the optimal ratio will depend on the amount of water in the catalyst fed to the reactants plus the amount produced by the reaction, so that the preferred molar ratio of alcohol to all water in the reaction will be at least 1:1 and more preferably at least 2:1.

The sixth or seventh state of the reagents may be fed to the reactor independently after or before mixing and the reaction process may be continuous or batch. However, typically, a continuous process is used.

Typically, the method of the sixth or seventh aspect of the present invention is carried out when the reactants are in the gas phase.

In another embodiment, the present invention extends to a method for producing an ethylenically unsaturated carboxylic acid or ester according to any of the related embodiments herein, which comprises the following steps: first, producing a catalyst according to any of the related embodiments herein.

Definition

Unless otherwise specified, the term "alkyl" as used herein means _C1 to _C12 alkyl and includes methyl, ethyl, vinyl, propyl, propenyl, butyl, butenyl, pentyl, pentenyl, hexyl, hexenyl and heptyl, typically, the alkyl is selected from methyl, ethyl, propyl, butyl, pentyl and hexyl, more typically methyl. Unless otherwise specified, an alkyl group may be straight or branched, cyclic, acyclic or partially cyclic/acyclic, unsubstituted, substituted or terminated with one or more substituents selected from the group consisting of halogen, cyano, nitro, ^-OR19 , -OC(O) ^R20 , -C(O) ^R21 , -C(O) ^{OR22, -NR23R24 ,} -C(O) ^NR25R26 , ^-SR29 , ^-C (O) ^SR30 , -C(S ^{) NR27R28} , unsubstituted or substituted aryl, or unsubstituted or substituted Het, wherein ^{R19 to} R ³⁰ herein and generally herein each independently represents hydrogen, halogen, unsubstituted or substituted aryl or unsubstituted or substituted alkyl, or in the case of R ²¹ halogen, nitro, cyano and amino and/or interspersed with one or more (typically less than 4) oxygen, sulfur, silicon atoms, or silane or dialkylsilane groups, or mixtures thereof. Typically, the alkyl group is unsubstituted, typically linear and typically saturated.

The term "alkenyl" is to be understood as "alkyl" above, with the difference that at least one carbon-carbon bond is unsaturated and the term therefore relates to _C2 to _C12 alkenyl.

The term "alkyl" or the like, unless otherwise indicated, should be construed as being consistent with the above definition of "alkyl", except that " _C0 alkyl" means not substituted by an alkyl group.

The term "aryl" as used herein includes five to ten membered, typically five to eight membered carbon ring aromatic or pseudoaromatic groups such as phenyl, cyclopentadienyl and indenyl anions and naphthyl, which groups may be unsubstituted or substituted with one or more substituents selected from the group consisting of unsubstituted or substituted aryl, alkyl (which group itself may be unsubstituted or substituted or terminated as defined herein), Het (which group itself may be unsubstituted or substituted or terminated as defined herein), halogen, cyano, nitro, OR19, OC(O) ^R20 , C(O) ^R21 , C(O) ^OR22 , ^NR23R24 , C(O) ^NR25R26 , ^SR29 , C(O) ^SR30 or C(S) ^NR27R28 , wherein ^R19 to R20 ^{are substituted or terminated} . R ³⁰ each independently represents hydrogen, unsubstituted or substituted aryl or alkyl (which alkyl itself may be unsubstituted or substituted or end-capped as defined herein), or, in the case of R ²¹ , halogen, nitro, cyano or amino.

The term "halogen" as used herein means a chloro, bromo, iodo or fluoro group, typically chloro or fluoro.

The term "Het" as used herein includes four to twelve, typically four to ten membered ring systems containing one or more heteroatoms selected from nitrogen, oxygen, sulfur and mixtures thereof, and which do not contain, contain one or more double bonds or may be non-aromatic, partially aromatic or fully aromatic in nature. The ring system may be monocyclic, bicyclic or fused. Each "Het" group identified herein may be unsubstituted or substituted with one or more substituents selected from the group consisting of halogen, cyano, nitro, pendooxy, alkyl (which alkyl itself may be unsubstituted or substituted or blocked as defined herein), ^-OR19 , -OC(O) ^R20 , -C(O) ^R21 , -C(O)OR22, -N( ^R23 ) ^R24 , -C(O)N( ^R25 ) ^{R26 , -SR29} , -C(O) ^SR30 , or -C(S)N( ^R27 ) ^R28 , wherein ^R19 to ^R30 each independently represents hydrogen, unsubstituted or substituted aryl or alkyl (which alkyl itself may be unsubstituted or substituted or blocked as defined herein), or with respect to R ²¹ for halogen, nitro, amino or cyano. The term "Het" therefore includes radicals such as optionally substituted azacyclobutyl, pyrrolidinyl, imidazolyl, indolyl, furanyl, oxazolyl, isoxazolyl, oxadiazolyl, thiazolyl, thiadiazolyl, triazolyl, oxatriazolyl, thiatriazolyl, oxazinyl, morpholinyl, pyrimidinyl, pyrazinyl, quinolinyl, isoquinolinyl, piperidinyl, pyrazolyl and piperazinyl. The substitution at Het may be at a carbon atom of the Het ring or, where appropriate, at one or more of the heteroatoms.

The "Het" group can also be in the form of an N-oxide.

Suitable optional alcohols for the catalytic reaction of the fourth and fifth aspects of the invention may be selected from: _C1 - _C30 alkanols, including aryl alcohols, which may be optionally substituted with one or more substituents selected from the following as defined ^herein : alkyl, aryl, Het, halogen, cyano, nitro, OR19, OC(O) ^R20 , C(O) ^R21 , C(O) ^OR22 , ^NR23R24 , C(O) ^NR25R26 , C(S) ^{NR27R28 , SR29 or} C( ^O ) ^SR30 . The most preferred alkanols are C ₁ -C ₈ alkanols such as methanol, ethanol, propanol, isopropanol, isobutanol, tert-butyl alcohol, phenol, n-butyl alcohol and chlorooctyl alcohol, especially methanol. Although monoalkanols are the most preferred, polyalkanols can also be used, which are typically selected from dioctanols such as diols, triols, tetraols and sugars. Typically, the polyalkanols are selected from 1,2-ethanediol, 1,3-propylene glycol, glycerol, 1,2,4-butanetriol, 2-(hydroxymethyl)-1,3-propanediol, 1,2,6-trihydroxyhexane, pentaerythritol, 1,1,1-tri(hydroxymethyl)ethane, mannose, transpeptidase, galactose and other sugars. Preferred sugars include sucrose, fructose and glucose. Particularly preferred alkanols are methanol and ethanol. The most preferred alkanol is methanol. The amount of alcohol is not critical. Generally, the amount used exceeds the amount of substrate to be esterified. Thus, the alcohol may also serve as the reaction solvent, although a separation or other solvent may be used as desired.

The term ageing is described, for example, in patent application WO 2009/003722. The general principles of ageing are described in The Chemistry of Silica: Solubility, Polymerisation, Colloid and Surface Properties and Biochemistry of Silica: Ralph K Iler, ed., 1979, John Wiley and Sons Inc., ISBN 0-471-02404-X, pp. 358-364. If this stage is carried out, the hydrogel is then additionally washed to remove any material used in the ageing process and to bring the solution to the correct pH for the addition of the catalytically active metal, depending on the choice of salt for the catalytically active metal.

Although the metal, metal oxide and metal oxide portion of any aspect of the invention or any preferred or optional feature thereof may be zirconium or einsteinium and zirconium oxide or einsteinium oxide, respectively, they are typically zirconium and zirconium oxide and portions of zirconium oxide.

The term "gel" as used herein is also known to the skilled person, but in case of doubt it can be considered as a solid network in which a fluid is dispersed. In general, a gel is a polymer network in which a fluid is dispersed. Cogel is a term used to indicate the incorporation of more than one original compound/moiety into the polymer network, which are usually silica and a metal oxide or salt, such as zirconia. Therefore, cogelation herein means the formation of a cogel.

A gel is therefore a sol that has set. A hydrogel is therefore a gel as defined herein in which the fluid is water. A xerogel is a gel that has been dried to remove the fluid. An aerogel is a gel in which the fluid has been replaced by a gas and therefore does not undergo the same contraction as a xerogel.

The term start in this article means the starting point of the formation of modified silicon dioxide.

The term "portion" as used herein with respect to a metal is used to refer to the form of the modifier metal on the modified support. Although the modifier metal generally forms part of the network, the modifier metal will be in the form of a discrete residue on the silicon dioxide matrix. Reference should be made to a total of up to two metal atoms or the like to refer to the monomeric and/or dimeric form of its residues. Appropriately, in the present invention herein, it has been found to be advantageous to have a portion in the form of a monomeric residue. Therefore, the term up to 2 modifier metal atoms or the like means in this article a total of 1 and/or 2 modifier metal atoms. In this context, 1 to 2 modifier metal atoms are preferred, particularly preferred is a total of 1 and/or 2 zirconium atoms in the moieties, most particularly 1 zirconium atom in the moieties.

The term monomer or dimer means having a monomer-like or dimer-like form or, in the case of residues on silicon dioxide, having a monomer or dimer residue form.

The percentage of modifier metal is unitless in this article because it refers to the number of metal atoms/total number of such atoms. It should be understood that such moieties may be in the form of non-monomer or non-dimeric clusters, but such clusters are still composed of modifier metal atoms.

Experiment Silica Support Description

Implementation Example 1

Fuji Silysia CARiACT Q10 silica (Q10) was dried in a laboratory oven at 160°C for 16 hours, after which it was removed from the oven and cooled to room temperature in a sealed flask stored in a desiccator. The surface area of this silica was 333 ^m2 /g, the pore volume was 1.0 ml/g, and the average pore size was 10 nm as determined by nitrogen adsorption/desorption isotherm analysis (Micromeretics Tristar II). A silanol number of 0.8 OH/ ^nm2 was found by TGA analysis. This silica was primarily composed of spherical silica beads with diameters ranging from 2-4 mm.

Example 2

Fuji Silysia CARiACT Q30 silica (Q30) was calcined in a tubular furnace at 900°C for 5 hours under nitrogen flow with a heating ramp rate of 5°C/min. It was then cooled to room temperature and stored in a sealed flask in a desiccator. This silica has a surface area of 112 ^m2 /g, a pore volume of 1.0 ml/g, an average pore size of 30 nm and is mainly composed of spherical silica beads with a diameter range of 2-4 mm.

Zr modification of silica carrier

Example 3 (0.92wt% Zr, single Zr on Q10)

0.542 g Zr(acac) ₄ (97%, Sigma Aldrich) was dissolved in 11 ml MeOH (99% Sigma Aldrich). In a separate flask, 10 g of silica from Example 1 was weighed. The weighed silica was then added to the Zr(acac) ₄ solution under stirring. Stirring was continued until all the Zr(acac) ₄ solution was absorbed into the pore volume of the silica. After the pore filling was completed, the Zr-modified silica was kept in a sealed flask for 16 hours with periodic stirring. Thereafter, the extra-pore solution was removed by filtration. This is followed by a drying step, in which the pore organic solvent is removed by passing a stream of nitrogen through the moistened Zr-modified silica at room temperature. Alternatively, the pore solvent is removed on a rotary evaporator under reduced pressure. After all the solvent has been removed, the Zr-modified silica support is calcined in a tubular furnace at 500°C under an air flow (1 l/min) with a heating ramp rate of 5°C/min and a final hold of 5 hours. After cooling, this yields a Zr-grafted silica support with 100% Zr utilization efficiency. The Zr loading (wt %) on the Zr-modified support is determined by powder energy dispersive X-ray fluorescence analysis (Oxford Instruments X-Supreme8000).

Example 4 (1.5wt% Zr, single Zr on Q10)

The support modification was carried out as described in Example 3, except that 0.874 g Zr(acac) ₄ was used.

Example 5 (2.3wt% Zr, single Zr on Q10)

The support modification was carried out as described in Example 3, except that 1.38 g Zr(acac) ₄ was used and 20 ml 1-PrOH (99% Sigma Aldrich) was used instead of MeOH. In addition, stirring was continued throughout the 16 h aging step before solvent removal. This resulted in a 90% Zr utilization efficiency.

Example 6 (2.7wt% Zr, single Zr on Q10)

The support modification was carried out as described in Example 5, except that 1.67 g Zr(acac) ₄ was used and 20 ml MeOH (99% Sigma Aldrich) was used instead of 1-PrOH. This resulted in 89% Zr utilization efficiency.

Example 7 (4.2wt% Zr, single Zr on Q10)

The support modification was carried out as described in Example 5, except that 2.56 g Zr(acac) ₄ was used and 20 ml toluene (99% Sigma Aldrich) was used instead of 1-PrOH. This resulted in a 93% Zr utilization efficiency.

Example 8 (0.7wt% Zr, single Zr on Q30)

The support modification was performed as described in Example 6, except that 0.43 g Zr(acac) ₄ was used and the silicon dioxide from Example 2 was used. This resulted in a 93% Zr utilization efficiency.

Example 9 (1.1wt% Zr, single Zr on Q10)

The support modification was carried out as described in Example 5, except that 2.15 g Zr(acac) ₄ was used and 20 ml MeOH was used instead of 1-PrOH. This resulted in a 47% Zr utilization efficiency.

Example 10 (2.2wt% Zr, single Zr on Q10)

The carrier modification was carried out as described in Example 9, except that 20 ml of toluene was used instead of MeOH. This resulted in a Zr utilization efficiency of 93%.

Example 11 (3.9wt% Zr, single Zr on Q10)

The support modification was carried out as described in Example 5, except that 3.19 g Zr(acac) ₄ was used and 20 ml heptane (99% Sigma Aldrich) was used instead of 1-PrOH. This resulted in 86% Zr utilization efficiency.

Example 12 (6.7wt% Zr, dimerized Zr on Q10)

The support modification was carried out as described in Example 5, except that 3.12 g [Zr(OPr) ₃ (acac)] 2 was used and 20 ml heptane was used instead of 1-PrOH. This resulted in a 95% Zr utilization efficiency.

Example 13 (2.2wt% Zr, trimerized Zr on Q30) (Comparison)

The support modification was carried out as described in Example 5, except that 1.16 g Zr(nOPr) ₄ (70 wt % in 1-propanol, Sigma Aldrich) was used. In addition, 10 g of silica from Example 2 was used instead of the silica from Example 1. This resulted in 100% Zr utilization efficiency.

Example 14 (6.0wt% Zr, trimerized Zr on Q10) (Comparison)

The support modification was carried out as described in Example 5, except for 3.35 g Zr(nOPr) ₄ (70 wt % in 1-propanol, Sigma Aldrich). This resulted in 100% Zr utilization efficiency.

Example 15 (8.0wt% Zr, pentameric Zr on Q10) (Comparison)

The carrier modification was carried out as described in Example 5, except that 2.67 g of zirconium (IV) ethoxide (97% Sigma Aldrich) and 1.77 g of acetic acid (ice, Sigma Aldrich) were dissolved in 20 ml of ethanol (anhydrous, Sigma Aldrich) instead of 1-PrOH. This resulted in 100% Zr utilization efficiency.

Hf modification of silica carrier

Example 16 (5.4wt% Hf, monomer Hf on Q10)

The support modification was carried out as described in Example 5, except that 1.37 g Hf(iOPr) ₄ (99% Sigma Aldrich) was dissolved in 20 ml 1-PrOH along with 1.32 g acetylacetone (99% Sigma Aldrich) and allowed to mix for 30 min before introducing 10 g silica from Example 1. This gave a 98% Hf utilization efficiency.

Example 17 (7.8wt% Hf, monomer Hf on Q10)

The support modification was carried out as described in Example 5, except that 2.00 g Hf(iOPr) ₄ was dissolved in 20 ml toluene together with 1.93 g acetylacetone and allowed to mix for 30 min before introducing 10 g of silica from Example 1. This resulted in 100% Hf utilization efficiency.

Example 18 (11.8wt% Hf, trimerized Hf on Q10) (Comparison)

The support modification was carried out as described in Example 5, except that 3.19 g Hf(iOPr) ₄ was dissolved in 20 ml toluene instead of 1-PrOH. This resulted in 100% Hf utilization efficiency.

HRTEM analysis of modified carrier

Example 19 (HRTEM analysis of single Zr)

The selected modified silica examples were subjected to high resolution transmission electron microscopy (HRTEM) analysis. For this purpose, the modified silica was cut into particles of 100-200 nm thickness using a thin slicer. These flaky particles were then mounted on a copper screen and an antistatic silicon vapor coating was applied. The mounted samples were then analyzed in transmission mode using a Tecnai G2 F20 (manufactured by FEI). The electron beam was set at an accelerating voltage between 100 and 300 kV with a spacing resolution of 1 nm. The electron beam was focused by a 30 pm vibrating membrane. HRTEM images were recorded so that 50-200 metal nanoparticles were included in the image at a magnification of 25 million times. This analysis was performed on modified silicon dioxide Examples 5, 7, 14, 15, 17, and 18. HRTEM images are shown in Figures 1-6.

Cs modification of modified carrier

Example 20 (3.2wt% Cs, 0.9wt% Zr, single Zr)

0.458 g of CsOH.H ₂ O (99.5% Sigma Aldrich) was weighed out in a glove box and dissolved in 20 ml of a 9:1 v/v MeOH:H ₂ O solvent mixture. 10 g of the modified silica from Example 3 was added to the CsOH solution under stirring. Stirring was continued for an additional 15 min, after which the sample was kept in a sealed flask for 16 hours with periodic stirring. Thereafter, the extra-pore solution was removed by filtration. This was followed by a drying step, in which the intra-pore solvent was removed by passing a stream of nitrogen through the moistened Cs/Zr-modified silica at room temperature. Alternatively, the intra-pore solvent was removed on a rotary evaporator under reduced pressure. After this step, the catalyst beads were placed in a drying oven at 110-120°C and left to dry for 16 hours. After cooling, a Cs/Zr/ _SiO2 catalyst with 90% Cs utilization efficiency was obtained. The Cs loading (wt%) on the catalyst was determined by powder energy dispersive X-ray fluorescence analysis (Oxford Instruments X-Supreme8000).

Example 21 (3.7wt% Cs, 0.9wt% Zr, single Zr)

The catalyst was prepared as described in Example 20, except that 0.534 g _CsOH.H2O was used.

Example 22 (4.0wt% Cs, 0.9wt% Zr, single Zr)

The catalyst was prepared as described in Example 20, except that 0.588 g _CsOH.H2O was used.

Example 23 (4.8wt% Cs, 0.9wt% Zr, single Zr)

The catalyst was prepared as described in Example 20, except that 0.716 g _CsOH.H2O was used.

Example 24 (5.1wt% Cs, 1.5wt% Zr, single Zr)

The catalyst was prepared as described in Example 20, except that 0.754 g _CsOH.H2O was used and the modified silica from Example 4 was used.

Example 25 (5.7wt% Cs, 1.5wt% Zr, single Zr)

The catalyst was prepared as described in Example 24, except that 0.852 g _CsOH.H2O was used.

Example 26 (6.7wt% Cs, 1.4wt% Zr, single Zr)

The catalyst was prepared as described in Example 24 except that 1.00 g of _CsOH.H2O was used.

Example 27 (7.7wt% Cs, 1.4wt% Zr, single Zr)

The catalyst was prepared as described in Example 24, except that 1.17 g _CsOH.H2O was used.

Example 28 (9.7wt% Cs, 2.0wt% Zr, single Zr)

The catalyst was prepared as described in Example 20, except that 1.37 g _CsOH.H2O was used and the modified silica from Example 5 was used. In addition, with the elimination of the filtration step, the Cs adsorption time was reduced from 16 hours to 2 hours. The excess organic solvent in the pore volume of the modified silica support was dried and 100% Cs utilization efficiency was obtained.

Example 29 (10.2wt% Cs, 2.0wt% Zr, single Zr)

The catalyst was prepared as described in Example 28, except that 1.45 g _CsOH.H2O was used.

Example 30 (10.8wt% Cs, 2.0wt% Zr, single Zr)

The catalyst was prepared as described in Example 28, except that 1.54 g _CsOH.H2O was used.

Example 31 (11.3wt% Cs, 2.0wt% Zr, single Zr)

The catalyst was prepared as described in Example 28, except that 1.62 g _CsOH.H2O was used.

Example 32 (9.2wt% Cs, 2.4wt% Zr, single Zr)

The catalyst was prepared as described in Example 20, except that 1.44 g _CsOH.H2O was used and the modified silica from Example 6 was used.

Example 33 (10.9wt% Cs, 2.4wt% Zr, single Zr)

The catalyst was prepared as described in Example 32, except that 1.74 g _CsOH.H2O was used.

Example 34 (13.0wt% Cs, 2.3wt% Zr, single Zr)

The catalyst was prepared as described in Example 32, except that 2.12 g _CsOH.H2O was used.

Example 35 (14.0wt% Cs, 2.3wt% Zr, single Zr)

The catalyst was prepared as described in Example 32, except that 2.30 g _CsOH.H2O was used.

Example 36 (12.3wt% Cs, 3.7wt% Zr, single Zr)

The catalyst was prepared as described in Example 20, except that 2.00 g of _CsOH.H2O was used and the modified silica from Example 7 was used.

Example 37 (12.6wt% Cs, 3.7wt% Zr, single Zr)

The catalyst was prepared as described in Example 36 except that 2.05 g _CsOH.H2O was used.

Example 38 (13.9wt% Cs, 3.6wt% Zr, single Zr)

The catalyst was prepared as described in Example 36 except that 2.30 g _CsOH.H2O was used.

Example 39 (15.4wt% Cs, 3.6wt% Zr, single Zr)

The catalyst was prepared as described in Example 36 except that 2.60 g _CsOH.H2O was used.

Example 40 (2.8wt% Cs, 0.7wt% Zr, single Zr)

The catalyst was prepared as described in Example 28, except that 0.37 g _CsOH.H2O was used and the modified silica from Example 8 was used.

Example 41 (3.4wt% Cs, 0.7wt% Zr, single Zr)

The catalyst was prepared as described in Example 40 except that 0.45 g _CsOH.H2O was used.

Example 42 (3.9wt% Cs, 0.7wt% Zr, single Zr)

The catalyst was prepared as described in Example 40 except that 0.51 g _CsOH.H2O was used.

Example 43 (4.1wt% Cs, 1.0wt% Zr, single Zr)

The catalyst was prepared as described in Example 20, except that 0.60 g of _CsOH.H2O was used and the modified silica from Example 9 was used.

Example 44 (4.6wt% Cs, 1.0wt% Zr, single Zr)

The catalyst was prepared as described in Example 43, except that 0.68 g _CsOH.H2O was used.

Example 45 (5.5wt% Cs, 1.0wt% Zr, single Zr)

The catalyst was prepared as described in Example 43, except that 0.82 g _CsOH.H2O was used.

Example 46 (9.1wt% Cs, 2.0wt% Zr, single Zr)

The catalyst was prepared as described in Example 20, except that 1.42 g _CsOH.H2O was used and the modified silica from Example 10 was used.

Example 47 (9.9wt% Cs, 1.9wt% Zr, single Zr)

The catalyst was prepared as described in Example 46 except that 1.55 g _CsOH.H2O was used.

Example 48 (13.8wt% Cs, 3.3wt% Zr, single Zr)

The catalyst was prepared as described in Example 20, except that 2.28 g _CsOH.H2O was used and the modified silica from Example 11 was used.

Example 49 (15.0wt% Cs, 3.3wt% Zr, single Zr)

The catalyst was prepared as described in Example 48, except that 2.51 g _CsOH.H2O was used.

Example 50 (14.0wt% Cs, 5.7wt% Zr, dimeric Zr) (Comparison)

The catalyst was prepared as described in Example 20, except that 2.34 g _CsOH.H2O was used and the modified silica from Example 12 was used.

Example 51 (15.0wt% Cs, 5.7wt% Zr, dimeric Zr) (Comparison)

The catalyst was prepared as described in Example 50, except that 2.54 g _CsOH.H2O was used.

Example 52 (16.1wt% Cs, 5.6wt% Zr, dimeric Zr) (Comparison)

The catalyst was prepared as described in Example 50 except that 2.76 g _CsOH.H2O was used.

Example 53 (17.3wt% Cs, 5.5wt% Zr, dimeric Zr) (Comparison)

The catalyst was prepared as described in Example 50 except that 3.01 g _CsOH.H2O was used.

Example 54 (6.0wt% Cs, 2.1wt% Zr, trimerized Zr) (Comparison)

The catalyst was prepared as described in Example 28, except that 0.81 g _CsOH.H2O was used and the modified silica from Example 13 was used.

Example 55 (7.7wt% Cs, 2.0wt% Zr, trimerized Zr) (Comparison)

The catalyst was prepared as described in Example 54 except that 1.06 g _CsOH.H2O was used.

Example 56 (13.6wt% Cs, 5.2wt% Zr, trimerized Zr) (Comparison)

The catalyst was prepared as described in Example 28, except that 2.03 g _CsOH.H2O was used and the modified silica from Example 14 was used.

Example 57 (14.9wt% Cs, 5.1wt% Zr, trimerized Zr) (Comparison)

The catalyst was prepared as described in Example 56, except that 2.26 g _CsOH.H2O was used.

Example 58 (16.1wt% Cs, 5.0wt% Zr, trimerized Zr) (Comparison)

The catalyst was prepared as described in Example 56, except that 2.48 g _CsOH.H2O was used.

Example 59 (17.3wt% Cs, 5.0wt% Zr, trimerized Zr) (Comparison)

The catalyst was prepared as described in Example 56 except that 2.70 g _CsOH.H2O was used.

Example 60 (12.3wt% Cs, 7.0wt% Zr, pentameric Zr) (Comparison)

The catalyst was prepared as described in Example 28, except that 1.82 g CsOH.H ₂ O was used and the modified silica from Example 15 was used.

Example 61 (14.0wt% Cs, 6.9wt% Zr, pentameric Zr) (Comparison)

The catalyst was prepared as described in Example 60 except that 2.12 g _CsOH.H2O was used.

Example 62 (15.7wt% Cs, 6.7wt% Zr, pentameric Zr) (Comparison)

The catalyst was prepared as described in Example 60 except that 2.42 g _CsOH.H2O was used.

Example 63 (18.9wt% Cs, 6.5wt% Zr, pentameric Zr) (Comparison)

The catalyst was prepared as described in Example 60 except that 2.99 g _CsOH.H2O was used.

Example 64 (8.8wt% Cs, 4.9wt% Hf, single Hf)

The catalyst was prepared as described in Example 28, except that 1.23 g _CsOH.H2O was used and the modified silica from Example 16 was used.

Example 65 (10.1wt% Cs, 4.9wt% Hf, single Hf)

The catalyst was prepared as described in Example 64 except that 1.43 g _CsOH.H2O was used.

Example 66 (11.4wt% Cs, 4.8wt% Hf, single Hf)

The catalyst was prepared as described in Example 64, except that 1.64 g _CsOH.H2O was used.

Example 67 (12.6wt% Cs, 4.7wt% Hf, single Hf)

The catalyst was prepared as described in Example 64, except that 1.84 g _CsOH.H2O was used.

Example 68 (11.1wt% Cs, 6.9wt% Hf, single Hf)

The catalyst was prepared as described in Example 28, except that 1.60 g of _CsOH.H2O was used and the modified silica from Example 17 was used.

Example 69 (12.7wt% Cs, 6.8wt% Hf, single Hf)

The catalyst was prepared as described in Example 68 except that 1.86 g _CsOH.H2O was used.

Example 70 (14.3wt% Cs, 6.7wt5 Hf, monomer Hf)

The catalyst was prepared as described in Example 68 except that 2.14 g _CsOH.H2O was used.

Example 71 (15.8wt% Cs, 6.6wt% Hf, single Hf)

The catalyst was prepared as described in Example 68 except that 2.41 g _CsOH.H2O was used.

Example 72 (13.7wt% Cs, 10.2wt% Hf, trimerized Hf) (Comparison)

The catalyst was prepared as described in Example 20, except that 2.28 g of _CsOH.H2O was used and the modified silica from Example 18 was used.

Example 73 (14.9wt% Cs, 10.0wt% Hf, trimerized Hf) (Comparison)

The catalyst was prepared as described in Example 72 except that 2.51 g _CsOH.H2O was used.

Example 74 (16.2wt% Cs, 9.9wt% Hf, trimerized Hf) (Comparison)

The catalyst was prepared as described in Example 72 except that 2.77 g _CsOH.H2O was used.

Example 75 (16.0wt% Cs, 3.4wt% Zr, 100% monomer Zr)

The catalyst was prepared as described in Example 20, except that 2.71 g _CsOH.H2O was used and 10 g of modified silica from Example 7 was used. Additionally, after drying the catalyst, it was crushed using a mortar and pestle and sieved to a size fraction of 0.1-1.0 mm. This gave a catalyst with 100% monomer content based on wt% Zr.

Example 76 (15.8wt% Cs, 3.6wt% Zr, 79% monomer Zr) (Comparison)

The catalyst was prepared as described in Example 75, except that 2.67 g CsOH.H ₂ O was used. In addition, 8.5 g of the modified silica from Example 7 and 1.5 g of the modified silica from Example 14 were used as catalyst supports. This gave a catalyst having a monomer content of 79% based on wt% Zr.

Example 77 (15.4wt% Cs, 3.9wt% Zr, 61% monomer Zr) (Comparison)

The catalyst was prepared as described in Example 75, except that 2.60 g CsOH.H ₂ O was used. In addition, 7 g of modified silica from Example 7 and 3 g of modified silica from Example 14 were used as catalyst supports. This gave a catalyst having a monomer content of 61% based on wt% Zr.

Example 78 (15.7wt% Cs, 4.4wt% Zr, 31% monomer Zr) (Comparison)

The catalyst was prepared as described in Example 75, except that 2.66 g CsOH.H ₂ O was used. In addition, 4 g of modified silica from Example 7 and 6 g of modified silica from Example 14 were used as catalyst supports. This gave a catalyst having a monomer content of 31% based on wt% Zr.

Example 79 (16.9wt% Cs, 5.0wt% Zr, 0% monomer Zr) (Comparison)

The catalyst was prepared as described in Example 75, except that 2.92 g CsOH.H ₂ O was used. In addition, 10 g of modified silica from Example 14 was used as catalyst support. This gave a catalyst having 0% monomer content based on wt% Zr.

Example 80 (Catalytic performance test)

The catalysts of Examples 20 to 79 were tested for the reaction of methyl propionate with formaldehyde in a laboratory-scale microreactor. For this purpose, 3 g of the catalyst were loaded in a fixed bed reactor with an internal tube diameter of 10 mm. The reactor was heated to 330° C. and pretreated by feeding a gasification stream consisting of 70 wt % methyl propionate, 20 wt % methanol, 6 wt % water and 4 wt % formaldehyde, fed from the distiller at 0.032 ml/min by a Gilson pump. This pretreatment was continued overnight. After pretreatment, a feed stream consisting of 75.6 wt% methyl propionate, 18.1 wt% methanol, 5.7 wt% formaldehyde and 0.6 wt% water was pumped to a distiller set at 330°C by a Gilson pump and then fed to a heated reactor set at 330°C containing a catalyst. The reactor outlet vapor was cooled and concentrated, and samples were collected at five different liquid feed rates (between 0.64-0.032 ml/min) to obtain conversions at different vapor/catalyst contact times. The liquid feed and concentrated Example reactor liquid product were analyzed by Shimadzu 2010 gas chromatograph with a DB1701 column. The sample composition was determined from the individual chromatograms and the yield and selectivity were determined at different contact times. Activity was defined as the reciprocal of the contact time (in seconds) required to obtain a 10% MMA+MAA yield for methyl propionate feed and was determined by interpolation of the contact time relative to the MMA+MAA yield graph. This interpolated contact time was then used to obtain the MMA+MAA selectivity at 10% MMA+MAA yield.

Example 81 (Accelerated Aging Test)

The sintering resistance of the catalysts was evaluated in an accelerated aging test. For this, 1 g of the catalyst was loaded in a U-tube stainless steel reactor and loaded in an oven. The oven was heated to 385° C. and a nitrogen stream (10 ml/min) was passed through a saturated distiller containing water heated to 92° C. This ensured that a feed stream with a water pressure of 0.75 bara was passed over the catalyst heated to 385° C. Periodically, the surface area of the catalyst samples was determined ex situ using nitrogen adsorption/desorption isotherm analysis (Micromeretics Tristar II). The sintering rate constant of each catalyst was determined using the measured surface area values and described in g ³ .m ^-6 .d ^-1 . The higher the sintering constant, the lower the sintering resistance of the catalyst. This test was performed on Example 32, Example 38, Example 57 and Example 63.

Example 82 and Example 83 (Comparison)

The examples were prepared according to the experimental examples disclosed in EP 1233330. In these examples, the silica employed was gelled silica in the form of spheres with diameters in the range of 2-4 mm, with a purity of over 99%, a total surface area of about 300-350 ^m2 /g, and a pore volume of 1.04 ^cm3 /g, of which 76% was provided by pores with diameters in the range of 7-23 nm.

Two catalysts were prepared by impregnating silica with an aqueous solution of zirconium nitrate sufficient to fill the pores of the support and drying in a rotary evaporator and subsequently in an air oven at 120°C for 2 hours. In one case, (Example 25), the impregnation of the zirconium solution was assisted by evacuating the pores of the support before adding the solution. In the other case (Example 26), the impregnation of the zirconium solution was carried out under atmospheric pressure of air. Caustic was then incorporated by a similar procedure using an aqueous solution of csium carbonate to obtain a csium content of 4% by weight (expressed as metal). The catalyst was then calcined at 450°C in air for 3 hours.

The catalysts were tested under the same conditions as described in Example 24. One catalyst (Example 25) failed to achieve 10% yield and exhibited the highest selectivity for achieving yield (9.6%).

HRTEM results of SiO2 substrate modified by Zr and Hf

HRTEM images of the Zr and Hf modified silica examples (Example 5, Example 7, Example 14, Example 15, Example 17 and Example 18) (Example 19) are shown in Figures 1 to 6. For the HRTEM images of monomeric Zr and Hf, it is difficult to clearly distinguish the Zr or Hf particles and this indicates the presence of very small Zr/Hf nanoparticles on the surface of the modified silica. This is attributed to the presence of Zr or Hf in the form of single atoms. For the trimerized Zr or Hf and pentamerized Zr examples, Zr or Hf clusters can be clearly distinguished on the modified support HRTEM images. This data confirms that the solution phase nuclei of the Zr or Hf species are transferred from the solution to the final catalyst formulation.

Icon data

Activity and selectivity data constructed from Table 1 and Table 2

Figure 7 shows the MMA+MAA selectivity (%) versus catalyst activity for the catalysts prepared in Examples 20 to 74. From this figure, it is apparent that trimerized Zr and Hf as well as pentamerized Zr result in lower MMA+MAA selectivity over the entire activity range tested. At equivalent Zr and Cs loadings, the dimerized Zr catalyst exhibits improved selectivity compared to the trimerized Zr catalyst.

Activity and selectivity data constructed from Table 3

Figure 8 shows the catalyst selectivity of the mixed monomer/trimer catalysts prepared in Examples 75 to 79. The Zr monomer content was calculated as % of the Zr content in monomer form. In these examples, the catalyst was crushed and sieved to 0.1-1.0 mm particles to increase sample homogeneity. From this figure, it is obvious that reducing the amount of Zr monomer in the formulation will result in a decrease in MMA+MAA selectivity.

Sintering resistance data constructed from Table 4

Figure 9 shows the catalyst sintering constants as determined by the advanced aging test described in Example 81. From Figure 9, it is apparent that the monomer Zr catalyst exhibits a lower sintering rate at comparable catalyst activity.

Attention should be paid to all texts and documents related to this application that were filed at the same time or before this specification and are open to public inspection with this specification, and the contents of all such texts and documents are incorporated into this article by reference.

All features disclosed in this specification (including any accompanying claims, abstracts and drawings) and/or all steps of any method or process so disclosed may be combined in any combination, except for at least some mutually exclusive combinations of such features and/or steps.

Unless expressly stated otherwise, each feature disclosed in this specification (including any accompanying patent claims, abstracts and drawings) may be replaced by alternative features that achieve the same, equivalent or similar purpose. Therefore, unless expressly stated otherwise, each feature disclosed is only one example of a series of general equivalent or similar features.

The present invention is not limited to the details of the aforementioned embodiments. The present invention extends to any novel features of the present invention disclosed in this specification (including any accompanying patent scope, abstract or diagram), or any novel combination thereof, or to any method disclosed thereby, or any novel features of the present invention disclosed in this specification, or any novel combinations thereof.

Claims (70)

A catalyst comprising a modified silica carrier, the modified silica carrier comprising a modifier metal, and a catalytic metal on the modified silica carrier, wherein the modifier metal is selected from one or more of zirconium and/or arsenic, and characterized in that at least a certain proportion of the modifier metal is present in a modifier metal portion having a total of at most 2 modifier metal atoms. A catalyst as described in claim 1, wherein at least 25% of the modifier metal is present in a modifier metal portion having a total of at most 2 modifier metal atoms. A catalyst comprising a modified silica carrier, the modified silica carrier comprising a modifier metal, and a catalytic metal located on the modified silica carrier, wherein the modifier metal is selected from one or more of zirconium and/or arsenic, and is characterized in that at least a certain proportion of the modifier metal is present in the modifier metal portion derived from a monomeric and/or dimerized modifier metal cation source at the beginning of the modification. A catalyst as described in claim 3, wherein at least 25% of the modifier metal is present in the modifier metal portion derived from a monomeric and/or dimerized modifier metal cation source at the start of modification. A catalyst as described in any one of claims 1 to 4, wherein the modifier metal is an adsorbate adsorbed on the surface of the silica carrier. A catalyst as described in any one of claims 1 to 4, wherein the modifier metal portion is a modifier metal oxide portion. A catalyst as described in any one of claims 1 to 4, wherein the silica carrier is in the form of silica gel. A catalyst as described in any one of claims 1 to 4, wherein the modifier metal is present in the carrier in the form of a cogel. A catalyst as described in any one of claims 1 to 4, wherein the modifier metal is present in the modified silica carrier in an effective amount to reduce sintering and improve the selectivity of the catalyst. A catalyst as described in any one of claims 1 to 4, wherein at least 30% of the modifier metal in the modified silica carrier is in the form of a moiety having a total of at most 2 metal atoms. The catalyst as described in claim 10, wherein the modifier metal in the modified silica carrier is a portion having a total of 1 metal atom. A catalyst as described in any one of claims 1 to 4, wherein the content of the modifier metal present is at most 7.6×10 ^-2 mol/mol silicon dioxide. The catalyst as described in any one of claims 1 to 4, wherein the content of the modifier metal is between 0.067×10 ^-2 and 7.3×10 ^-2 mol/mol silicon dioxide. A catalyst as described in any one of claims 1 to 4, wherein the content of the modifier metal present is at least 0.1×10 ^-2 mol/mol silicon dioxide. A catalyst as described in any one of claims 1 to 4, wherein the catalytic metal is one or more alkali metals. A catalyst as described in any one of claims 1 to 4, wherein the catalytic metal is cesium. A catalyst as described in any one of claims 1 to 4, wherein the carrier comprises isolated silanol groups (-SiOH) at a content of <2.5 groups/nm2. A catalyst as described in any one of claims 1 to 4, wherein the catalytic metal is present in the range of 0.5-7.0 mol/mol modifier metal. A catalyst as described in claim 3 or 4, wherein at the start of the modification, the monomer and/or dimerized modifier metal cation is a compound having one or more stable ligands attached to the modifier metal cations, the stable ligands being selected from molecules having unshared electron pairs containing oxygen or nitrogen atoms capable of forming a 5- or 6-membered ring with a zirconium or bismuth atom, including diketones, diimines, diamines, diols, dicarboxylic acids or derivatives thereof, or molecules having two different functional groups and in either case having respective N or O atoms and N or O atoms separated by 2 or 3 atoms to form a 5- or 6-membered ring. A catalyst as described in any one of claims 1 to 4, wherein the modifier metal compound is in the form of an organic metal complex and a metal salt. A modified silica carrier for a catalyst, comprising a silica carrier and a modifier metal, wherein the modifier metal is selected from one or more of zirconium and/or arsenic, and characterized in that at least a certain proportion of the modifier metal is present in a modifier metal portion having a total of at most 2 modifier metal atoms. A modified silica carrier as described in claim 21, wherein at least 25% of the modifier metal is present in a modifier metal portion having a total of at most 2 modifier metal atoms. A modified silica carrier for a catalyst, comprising a silica carrier and a modifier metal, wherein the modifier metal is selected from one or more of zirconium and/or arsenic, and characterized in that at least a certain proportion of the modifier metal is present in the modifier metal portion derived from a monomeric and/or dimerized modifier metal cation source at the beginning of the modification. A modified silica carrier as described in claim 23, wherein at least 25% of the modifier metal is present in the modifier metal portion derived from a monomeric and/or dimerized modifier metal cation source at the start of modification. A modified silica carrier as described in any one of claims 21 to 24, wherein the modifier metal is an adsorbate adsorbed on the surface of the silica carrier. A modified silicon dioxide carrier as described in any one of claims 21 to 24, wherein the modifier metal portion is a modifier metal oxide portion. A modified silica carrier as described in any one of claims 21 to 24, wherein the silica carrier is in the form of silica gel. A modified silica carrier as described in any one of claims 21 to 24, wherein the modifier metal is present in the carrier in the form of a co-gel. A modified silica carrier as described in any one of claims 21 to 24, wherein the modifier metal is present in the modified silica carrier in an effective amount to reduce sintering. A modified silica carrier as described in any one of claims 21 to 24, wherein at least 30% of the modifier metal in the modified silica carrier is in the form of a moiety having a total of at most 2 metal atoms. A modified silicon dioxide carrier as described in claim 30, wherein the modifier metal in the modified silicon dioxide carrier is a portion having a total of 1 metal atom. A modified silica carrier as described in any one of claims 21 to 24, wherein the content of the modifier metal present therein is at most 7.6×10 ^-2 mol/mol silica. A modified silica carrier as described in any one of claims 21 to 24, wherein the content of the modifier metal is between 0.067×10 ^-2 and 7.3×10 ^-2 mol/mol silica. A modified silica carrier as described in any one of claims 21 to 24, wherein the content of the modifier metal present therein is at least 0.1×10 ^-2 mol/mol silica. A modified silica carrier as described in any one of claims 21 to 24, wherein the carrier comprises isolated silanol groups (-SiOH) at a content of <2.5 groups/nm2. A modified silica carrier as described in claim 23 or 24, wherein at the beginning of the modification, the monomeric and/or dimeric modifier metal cations are compounds having one or more stable ligands attached to the modifier metal cations, the stable ligands being selected from molecules having unshared electron pairs containing oxygen or nitrogen atoms capable of forming a 5- or 6-membered ring with a zirconium or bismuth atom, including diketones, diimines, diamines, diols, dicarboxylic acids or their derivatives, or molecules having two different functional groups and in either case having respective N or O atoms and N or O atoms separated by 2 or 3 atoms to form a 5- or 6-membered ring. A modified silica carrier as described in any one of claims 21 to 24, wherein the modifier metal compound is in the form of an organic metal complex and a metal salt. A modified silicon dioxide carrier as described in any one of claims 21 to 24, wherein the carrier comprises the zirconium or benzene modifier metal portion present and present in an amount of <2.5 parts/nm2. A modified silica carrier as described in any one of claims 21 to 24, wherein the carrier contains isolated silanol groups (-SiOH) in a content of >0.1 and <2.5 groups/nm2. A modified silicon dioxide carrier as described in any one of claims 21 to 24, wherein the carrier comprises the zirconium or benzene modifier metal portion in an amount >0.025 and <2.5 parts/nm2. A method for making a modified silica carrier for a catalyst comprises the following steps: i. providing a silica carrier having isolated silanol groups; ii. contacting the silica carrier with a monomeric zirconium or bismuth modifier metal compound so that the modifier metal is adsorbed on the carrier, adsorbed on at least 25% of the isolated silanol groups. The method of claim 41, wherein the silica carrier in step i is treated to provide separated silanol groups (-SiOH) at a content of <2.5 groups/nm2. The method as described in claim 41 further comprises the step of removing any solvent or liquid carrier of the modifier metal compounds. The method as described in claim 41 further comprises the step of calcining the modified support for a time and temperature sufficient to convert the monomeric zirconium or ebonite compound adsorbed on the surface into an oxide or hydroxide of zirconium or ebonite in preparation for catalyst impregnation. A method for manufacturing a catalyst, comprising the method as described in claim 44, further comprising the step of treating the calcined modified silicon dioxide with a catalytic metal to impregnate the modified silicon dioxide with the catalytic metal to form the catalyst. The method as described in claim 45 further comprises the step of calcining the catalyst. A method as described in any one of claims 41 to 46, wherein the concentration of the silanol groups is reduced prior to treatment with the modifier metal compounds by calcination, chemical dehydration or other suitable methods. A method as described in any one of claims 41 to 46, wherein the modifier metal cation source is a solution of the compounds, so that the compounds are in a dissolved state when contacting the carrier to be adsorbed on the carrier. A method as described in any one of claims 41 to 46, wherein one or more stabilizing ligands are attached to the modifier metal cations to at least partially form the compounds and are selected from molecules with unshared electron pairs containing oxygen or nitrogen atoms capable of forming a 5- or 6-membered ring with a zirconium or arsenic atom, including diketones, diimines, diamines, diols, dicarboxylic acids or derivatives thereof, or molecules having two different functional groups and in either case having respective N or O atoms and N or O atoms separated by 2 or 3 atoms to form a 5- or 6-membered ring. A method as described in claim 49, wherein the stabilizing ligands form a complex with the monomer modifier element. A method as described in any one of claims 41 to 46, wherein the silanol concentration on the silica support is 0.1-2.5 silanol groups/nm2 when in contact with the modifier metal compound. A method as described in any one of claims 41 to 46, wherein at least 30% of the modifier metal in the modifier metal compounds is in the form of monomeric modifier metal compounds when the source thereof is contacted with the carrier to adsorb the compounds on the carrier. A method as described in any one of claims 41 to 46, wherein the silica carrier is dried or calcined before being treated with the modifier metal compounds. A method as claimed in claim 45 or 46, wherein the modified silicon dioxide formed by contacting with the modifier metal compounds is dried or calcined before adding the catalytic metal. A method as claimed in any one of claims 41 to 46, wherein the silicon dioxide is in gel form prior to treatment with the modifier metal compounds. A method as described in any one of claims 41 to 46, wherein the modifier metal is dispersed on the inner and outer surfaces of the silicon dioxide carrier by adsorption. A method as described in any one of claims 41 to 46, wherein the modifier metal compound is in the form selected from an organometallic complex and a metal salt. A method as described in claim 45 or 46, wherein the catalytic metal is one or more alkaline metals. The method as described in claim 58, wherein the catalytic metal is cesium. A method for producing a catalyst as described in any one of claims 1 to 4, comprising the steps of forming a modified silica carrier as described in any one of claims 21 to 24 and contacting the modified silica carrier with a solution containing a catalytic metal to impregnate the modified silica carrier with the catalytic metal. A method for producing an ethylenically unsaturated carboxylic acid or ester, comprising the steps of contacting formaldehyde or a suitable source thereof with a carboxylic acid or ester in the presence of a catalyst, wherein the catalyst is as described in any one of claims 1 to 4. A method as claimed in claim 61, wherein the step of contacting formaldehyde or a suitable source thereof with a carboxylic acid or ester in the presence of a catalyst occurs in the presence of an alcohol. The method as described in claim 61, wherein the carboxylic acid or ester is selected from methyl propionate or propionic acid. A method for preparing an ethylenically unsaturated acid or ester comprises reacting an alkanoic acid or ester of the formula R ¹ -CH ₂ -COOR ³ with formaldehyde or a suitable source of formaldehyde of the formula (I) as defined below:

wherein R ⁵ is methyl and R ⁶ is H; X is O; m is 1; and n is an integer between 1 and 20; or formaldehyde or any mixture of suitable sources of formaldehyde of formula (I) as defined above; contacted in the presence of a catalyst as described in any one of claims 1 to 4; wherein R ¹ is hydrogen or an alkyl group having 1 to 12 carbon atoms and R ³ may also independently be hydrogen or an alkyl group having 1 to 12 carbon atoms. A method as claimed in claim 64, wherein the step of contacting formaldehyde or a suitable source thereof with an alkanoic acid or ester in the presence of a catalyst also occurs in the presence of an alkanol. The method as described in claim 65, wherein the alkanol is methanol. The method as described in claim 64, wherein the ethylenically unsaturated acid or ester is methyl methacrylate or methacrylic acid. A method for producing a modified silica carrier comprises the following steps: providing a silica carrier having silanol groups; treating the silica carrier with a monomeric and/or dimerized modifier metal compound so that the modifier metal is adsorbed on the surface of the silica carrier by reacting with the silanol groups, wherein the modifier metal is selected from one or more of zirconium and/or arsenic, and wherein the adsorbed modifier metal atoms are sufficiently spaced apart from each other to substantially prevent oligomerization with adjacent modifier metal atoms. The method of claim 68, wherein the spacing of the modifier metal atoms is achieved by: a) reducing the concentration of silanol groups on the silica support and/or b) attaching stabilizing ligands of sufficient size to the modifier metal cations. A method as described in claim 68 or 69, wherein the modified silicon dioxide carrier is as described in any one of claims 21 to 24.