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WO2007000068A1 - Procede de fabrication d'un materiau catalytique actif - Google Patents

Procede de fabrication d'un materiau catalytique actif Download PDF

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Publication number
WO2007000068A1
WO2007000068A1 PCT/CH2006/000338 CH2006000338W WO2007000068A1 WO 2007000068 A1 WO2007000068 A1 WO 2007000068A1 CH 2006000338 W CH2006000338 W CH 2006000338W WO 2007000068 A1 WO2007000068 A1 WO 2007000068A1
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WIPO (PCT)
Prior art keywords
catalyst
vanadia
xylene
active material
catalytic
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PCT/CH2006/000338
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English (en)
Inventor
Anika Bareiss
Andreas Reitzmann
Björn Schimmöller
Heiko Schulz
Sotiris-Emanuel Pratsinis
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Eidgenoessische Technische Hochschule Zurich ETHZ
Karlsruher Institut fuer Technologie KIT
Original Assignee
Eidgenoessische Technische Hochschule Zurich ETHZ
Universitaet Karlsruhe
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Publication of WO2007000068A1 publication Critical patent/WO2007000068A1/fr
Anticipated expiration legal-status Critical
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    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C51/00—Preparation of carboxylic acids or their salts, halides or anhydrides
    • C07C51/16—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation
    • C07C51/21—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation with molecular oxygen
    • C07C51/255—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation with molecular oxygen of compounds containing six-membered aromatic rings without ring-splitting
    • C07C51/265—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation with molecular oxygen of compounds containing six-membered aromatic rings without ring-splitting having alkyl side chains which are oxidised to carboxyl groups
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/002—Mixed oxides other than spinels, e.g. perovskite
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/16—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of arsenic, antimony, bismuth, vanadium, niobium, tantalum, polonium, chromium, molybdenum, tungsten, manganese, technetium or rhenium
    • B01J23/20—Vanadium, niobium or tantalum
    • B01J23/22—Vanadium
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/02—Impregnation, coating or precipitation
    • B01J37/0215—Coating
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/08—Heat treatment
    • B01J37/082—Decomposition and pyrolysis
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/34—Irradiation by, or application of, electric, magnetic or wave energy, e.g. ultrasonic waves ; Ionic sputtering; Flame or plasma spraying; Particle radiation
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B41/00—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone
    • C04B41/009—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone characterised by the material treated
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B41/00—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone
    • C04B41/45—Coating or impregnating, e.g. injection in masonry, partial coating of green or fired ceramics, organic coating compositions for adhering together two concrete elements
    • C04B41/50—Coating or impregnating, e.g. injection in masonry, partial coating of green or fired ceramics, organic coating compositions for adhering together two concrete elements with inorganic materials
    • C04B41/5025—Coating or impregnating, e.g. injection in masonry, partial coating of green or fired ceramics, organic coating compositions for adhering together two concrete elements with inorganic materials with ceramic materials
    • C04B41/5041—Titanium oxide or titanates
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B41/00—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone
    • C04B41/80—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone of only ceramics
    • C04B41/81—Coating or impregnation
    • C04B41/85—Coating or impregnation with inorganic materials
    • C04B41/87—Ceramics
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J2523/00—Constitutive chemical elements of heterogeneous catalysts
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B2111/00—Mortars, concrete or artificial stone or mixtures to prepare them, characterised by specific function, property or use
    • C04B2111/00474—Uses not provided for elsewhere in C04B2111/00
    • C04B2111/0081—Uses not provided for elsewhere in C04B2111/00 as catalysts or catalyst carriers

Definitions

  • the present invention relates to a process for the production of a catalyst, to catalysts obtained by such a production method, to the use of such catalysts in chemical reactions.
  • the invention relates to catalysts and the manufacture of catalysts useful in oxidation reactions, like partial oxidation of xylene to phthalic acid anhydride (PA).
  • PA phthalic acid anhydride
  • the present invention relates to a process for the production of a catalyst comprising the step of deposition of gasborne, catalytic active material on porous supports. Further, the invention relates to a process for the production of a catalyst comprising the step of deposition of catalytic active gas phase-made particles on porous supports, preferably foam- and/or sponge like structure.
  • the invention relates to a process for the production of a catalyst comprising the step of deposition of particles made by flame spray pyrolysis on ceramic foams.
  • the present invention relates to catalysts obtained by such a manufacturing process. Further, the present invention relates to the use of catalysts obtained by such a manufacturing process in chemical reactions.
  • the invention relates to the use of thus obtained catalyst for the manufacture of phthalic anhydride.
  • FSP flame-spray pyrolysis
  • porous supports e.g. ceramic foams
  • PA phthalic anhydride
  • vanadia/titania is one of the most commonly used catalysts [5, 6].
  • Eggshell catalyst pellets of millimeter size with solid, inert cores are packed into a fixed bed [7].
  • the thickness of the shell typically amounts up to 300 micrometers.
  • This special catalyst type is used to prevent activity and PA selectivity reduction by mass transfer limitations inside the porous catalyst.
  • the pressure drop over packed beds limits the PA productivity.
  • the pellet shape determines the catalyst bed porosity which influences the pressure drop which often limits the space-time-yields of fixed bed reactors. Therefore hollow cylinders or rings are commonly used as catalyst shapes to keep the pressure drop as low as possible [5, 8, 9].
  • the partial oxidation of o-xylene to PA is a highly exothermic reaction (typically 1300 to 1800 kJ mol "1 ) [5].
  • the evolving heat has to be transferred effectively out of the catalyst bed, because hot spots above 500 °C deactivate the catalyst irreversibly [7, 8] and lead to an increased risk of thermal reactor runaway [10].
  • Porous supports such as ceramic foams can improve the heat transfer compared to packed beds of spheres [11].
  • An open-pore structure and a high void fraction lead to a lower pressure drop and an increased heat transfer by radiation over the foam height compared to packed beds [12].
  • the possible formation of a turbulent gas flow can increase the heat and mass transfer compared to a laminar flow in honeycombs [12, 13].
  • thermal conductivity and surface properties can be modified because a large variety of foam materials is available [14].
  • foams can combine properties of packed beds and honeycombs in a beneficial way [11, 12].
  • the anatase crystal structure shows higher catalytic activity than other crystal structures.
  • a high dispersion of vanadia on titania, enabling a good accessibility, is regarded crucial for a high activity.
  • the activity is also influenced by the morphology of the vanadia.
  • Monomeric and polymeric vanadia species show enhanced reactivity in selective oxidations as compared to crystalline vanadia.
  • the selectivity is mainly influenced by the oxidation state of the vanadium itself and the modifications taking place during the catalytic reaction [15]. Disclosure of the Invention
  • the manufacture of a catalyst is manifested by a process comprising the step of dry s deposition of gasborne catalytic active material on a porous support wherein the catalytic active material have an external surface area (measured e.g. by nitrogen adsorption) between 0.3 and 1000m 2 /g.
  • One or more of the objectives as described herein are also achieved by a process comprising the step of deposition of particles on a porous support with a o foam- and/or sponge-like structure.
  • this invention discloses i) a process of coating a solid foam- and/or sponge like material with flame-made catalytic active mixed metal oxides; ii) a successful working system in terms of production and coating; iii) application of the o produced catalysts in an exemplary chemical reaction, the oxidation of xylene to PA.
  • Vanadia doped titania nano particles were produced in single step flame-spray process.
  • the direct deposition of flame-made vanadia/titania could be controlled by the pressure drop over the filter and the foam, resulting in low dispersion (patchy) to high dispersion (almost homogenous) coatings.
  • the mass of deposited V 2 CVTiO 2 was controlled by the pressure drop over the filter and the foam and by the sampling time.
  • this invention compares catalysts according to this invention with known wet-phase made catalyst.
  • the catalyst manufactured contained 7 and 10 wt.% V 2 O 5 , most commonly used for the oxidation of xylene to PA [6, 16].
  • the influence of external surface area, deposition time and pressure drop over the filter and deposited mass of vanadia/titania on the foam are investigated systematically.
  • Catalytic activity and selectivity of FSP-made catalysts are compared to a wet-phase made reference catalyst.
  • the catalyst according to the invention revealed significantly higher catalytic activity and similar selectivity to phthalic anhydride at high o-xylene conversion compared to the wet-phase made catalyst. Further, it was found that in the tested reaction low dispersion coatings and V 2 O 5 ZTiO 2 with small external surface area showed higher yield than the high dispersion coating and vanadia/titania with high external surface area.
  • catalysts according to the invention combine high catalytic yield with favorable support structures (low pressure drop, good heat transfer), highly porous coatings and fast production routes. These properties make the catalysts according to the invention interesting for possible applications in catalytic reaction.
  • Figure 1 Scheme of the FSP-setup.
  • the precursor is dispersed by oxygen and the resulting spray is ignited by a premixed methane/oxygen flame. Supplying additional oxygen assures oxidation of all precursors in the flame.
  • Figure 3 Production conditions of the powder produced by spray flame pyrolysis. Specific surface area (squares), BET-diameter (circles) and anatase crystal size (diamonds) of the vanadia/titania with constant flame conditions: 5 ml min-1 precursor; 5 nL min-1 dispersion gas. Precursor concentration was in the range of 0.1 to 3.4M (pure) titamurn-tetra-iso-propoxide.
  • Figure 4 TEM images with electron diffraction patterns (inset) of the flame made vanadia/titania powders with (a) high (93 m 2 g "1 ), 17 g(V 2 ⁇ 5 /Ti ⁇ 2 ) h "1 , and (b) small (53 m 2 g '1 ), 87 h "1 , specific surface area.
  • FIG. 5 TEM image (a) with a electron diffraction pattern (inset) of the uncalcinated powder fraction and SEM image (b) of the calcinated (45O 0 C, Ih) split fraction of the wet-phase reference catalyst-
  • Figure 6 Pore size distributions of (a) the flame-made catalytic active material and (b) the split catalysts. Vanadia/titania with small (53 m 2 g "1 ) and high (93 m 2 g "1 ) specific surface area, FSP-made split and wet-phase made reference. • x axis in a and b represents the pore diameter in nm • left y axis in a and right y axis in b represent the pore volume in arbitary units
  • High dispersion coating (b) was achieved by a constant pressure drop above filter of 80 mbar Deposition time was 300s, deposited mass was
  • Low dispersion coating (c) was achieved by a constant volume flow of 12.5 m 3 h "1 of the vacuum pump. Deposition time was 150s, deposited mass was 38 mg.
  • Deposited mass was 50 mg resulting in a coating thickness ranging from 150 to 200 ⁇ m.
  • Figure 9 Dependence of deposited vanadia/titania mass (squares) on the foam with respect to pressure drop (a) behind filter and sampling time (b). Average BET-diameter (circles) of the active component does not change by changing deposition conditions.
  • Figure 10 Scheme of the experimental set-up for direct deposition of FSP- made particles on porous supports.
  • • 1 indicates the inlet of premixed CH 4 ZO 2 for the supporting flame
  • • 2 indicates the inlet of the metal containing liquid precursor
  • Particles refers to solid material having a size / size distribution of any particles in the range of 10 "9 to 10 "6 m. Characterization of the particles is possible by directly indication of the size, which is in general lnm - lO ⁇ m, preferably 5 - 200 nm, for example 20 nm. Alternatively, an indirect characterization is possible by indicating the external surface area per mass; e.g. 0.3 - 1000m 2 /g (e.g. measured by nitrogen adsorption, also referred to as specific surface area SSA), preferably above 53m 2 /g; regardless of the agglomerate size.
  • specific surface area SSA specific surface area
  • Particles according to the invention may consist of organic, inorganic matter such as metals, -oxides, -nitrides, -sulfides, -halogenides, -borides, -phosphates and any mixtures of those. Particles can be produced by any method known to the skilled person, such as gas, plasma or wet- phase synthesis. “Particles” also include “catalytic active material” as described in this invention.
  • Catalytic active material generally refers to any material that is solid and has a catalytic effect in a chemical reaction. Preference is given to such catalytic material that is already used in commercial processes, such as metals and metal oxides and any mixture of those; e.g. Pd, Pt, V 2 O 5 , TiO 2 , V 2 O 5 ATiO 2 .
  • Airborne particles refers to particles that are dispersed in an air stream.
  • porous support refers to any material that is suitable to support the catalytic active material and can be penetrated by a particle laden gas stream. Supports maybe of metal or alloys; Carbides such as SiC; ceramic materials such as oxides of Aluminium, Silicium or Zirconium and any mixture of those.
  • the porous 5 support exhibits open or partially open cells, e.g. foam- and/or sponge like structures.
  • the porous support and the catalytic active material may be the same material.
  • the porous support may consist of solid or porous material itself.
  • the porous support may be, depending on the o intended use, made of stiff material or of flexible material. Such supports are known in the field and commercially available or obtainable according to known methods. "Coating” refers to the particles deposited on the support. It is understood that the definitions, specifications, and embodiments their preferences and particular preferences as provided herein may be combined at will. s Further, selected definitions or specifications may not apply.
  • the invention relates to a process for the production of a catalyst comprising the step of dry deposition of gasborne. catalytic active material on a porous support wherein the catalytic active material have an external surface area o between 0,3 to 1000m 2 /g.
  • dry deposition refers to the fact that no solvent is used in this process. This is an advantage, as it overcomes various problems of known processes for catalyst manufacture. In particular, the process is simpler (no solvent handling), safer (risk of explosion, hazardous solvents) and more cost efficient (less 5 equipment necessary; no need to remove solvent from the catalyst, no waste disposal).
  • the particle-laden gas stream flows through a porous support of any shape in any direction.
  • the flow of the gas stream may be varied in a broad range.
  • nano particles can be deposited in a o laminar, turbulent or intermediate flow; preference is given to a laminar flow.
  • Deposition of particles can be controlled e.g. by the gas flow rate, particles size, deposition time, flow regime or pressure drop over the foam.
  • the Carrier fluid as used in this process can be any gas such as air, combustion gases, nitrogen, argon, oxygen, off-gases or any combination thereof.
  • Deposition temperatures may vary in a broad range. Generally, temperatures below ambient up to 2000°C are feasible.
  • the deposition temperature is chosen to affect the particles to sinter onto the porous support. Such sintering may improve properties of the thus manufactured catalyst; e.g. by increasing the catalytic yield or improving mechanical properties of the catalyst such as the adhesion of the particles to the support.
  • Deposition times can vary in a broad range. Typically, deposition times are in the range from seconds up to hours, preferably from seconds to a few minutes. Such deposition times give adequate coatings, being much faster than common coating techniques such as dip-coating or precipitation.
  • the deposited catalytic active material according to the present invention is "gasborne". This term describes the fact that the particles are dispersed in a gas stream that passes the porous support and, upon passing the support, at least part of the material is deposited on said support.
  • the gas stream consist of air.
  • the particles employed in the process are prepared beforehand by known methods and are dispersed in a. gas flow.
  • the particles employed are directly produced, e.g. by condensation or by a chemical reaction, in the gas flow (c.f. examples).
  • the particles used in the manufacturing of the catalyst are manufactured by flame synthesis.
  • the particles are manufactured by flame spray pyrolysis (FSP).
  • FSP flame spray pyrolysis
  • a device for FSP is shown in Figure 1.
  • the liquid precursor is fed to a flame, where it converts to the catalytic active material having the desired particle size.
  • the resulting gas-flow, which contains the catalytic active material passes a deposition zone where the porous support is located ( Figure 2).
  • the thus formed catalyst may be removed once the desired amount of material is deposited.
  • the catalytic active material is selected from the group OfV 2 O 5 ; V 2 O 5 /TiO 2 ; V 2 0 5 /Cs 2 0/Ti0 2; e.g. V 2 O 5 ATiO 2 .
  • Coatings can range from nanometers up to a few millimeters thickness. Most commonly used are coatings of micrometer size. In a preferred embodiment, the coating has a thickness of about 50 - 500 micrometers, preferably 100 — 200 micrometers. Coatings can range from low (patchy) to high dispersion (evenly distributed) on the support surface.
  • surface properties of the catalytic active coating are modified during deposition and/or after the deposition and/or in the application of the catalyst. Such further modification may be beneficial to increase catalyst performance.
  • particle surfaces can be modified after deposition on the porous support by various treatments, such as atomic layer deposition, chemical vapor deposition or thermal treatment (e.g. sintering, activation).
  • the catalysts obtained according to the described process are ready-to-use without any further processing steps, meaning the manufactured catalyst can be installed right after the deposition step in the reactor without any post processing steps to activate (sintering) the catalytic active material.
  • particles in particular nano particles retain an open-pore structure with void fractions ranging from 40 up to 99.9 % when subjected to the manufacturing process as described herein. Without being bound to theory, it is believed that this results in a high accessibility and thus facilitating gas penetration into the catalytic active layer.
  • deposition mechanisms of the particles on the support can take place by impaction, therrnophoresis, diffusion or any combination of the aforementioned mechanisms.
  • the porous support is defined above. Preference is given to foam- and/or sponge-like structures, preferably metal, ceramic or carbide foams.. In a preferred embodiment, the porous support increases the heat transfer an reduces the pressure drop in the reactor in comparison to commonly used eggshell or full contact catalysts.
  • the manufacturing of a catalyst according to the process as described above meets one or more of the following criteria: i) a fast and easy process ; ii) a ready-to-use catalysts or catalyst preforms; iii) deposition times of catalytic active material are short (and faster when compared with common coating techniques such as dip-coating or precipitation).
  • the invention relates to a catalyst obtained by a process as described herein.
  • a preferred catalyst is obtained by a process as described herein has void fractions of the coating in the range of 40 - 99.9%.
  • a catalyst according to this invention meets one or more of the following criteria: i) decreased the pressure drop over a fixed bed (which, in turn increases the productivity of the process) when compared to commonly used catalysts such as spheres, solid or hollow cylinders; ii) increased radial and axial heat transfer within the reactor when compared to commonly used catalysts such as spheres, solid or hollow cylinders; iii) improved catalytic parameters, such as activity, selectivity, conversion, yield and lower residence tune of reactants; iv) facilitates any reaction with inner mass transport limitation.
  • the invention relates to the use of a catalyst as described herein in a chemical reaction.
  • any endo- or exothermic reaction such as oxidation, partial oxidation, waste gas cleaning, hydrogenation, steam reforming, or dehydrogenation, maybe subject to the use of a catalyst as described herein.
  • Preferred reactions are oxidation reactions, such as the oxidation of xylene to obtain PA.
  • a catalyst as described herein in a chemical reaction provides one or more of the following advantages: i) a reduced risk of hot spots or thermal runaways (which may deactivate the catalysts irreversibly) when compared to commonly used shaped catalyst bodies, such as spheres, solid or hollow cylinders; ii) facilitated heat transfer (by radiation) in high temperature reactions.
  • the invention relates to a catalyst comprising i) a ceramic foam and ii) catalytic active particles, wherein the particles are seleced from the group of TiO 2 /V 2 O 5 or TiO 2 /V 2 O 5 /Cs 2 O wherein the particles materials have an external surface area between 0.3 to 100OmVg.
  • the following examples relate to the manufacture and characterization of catalysts suitable for the oxidation of xylene to PA and to the use of the obtained catalysts in this reaction.
  • the examples are intended to illustrate the invention. These examples are not meant to limit the invention.
  • Precursor preparation For the precursor preparation, the solvents xylene o (Fluka, >98.5%) and acetonitrile (Fluka, >99.5%) were mixed (11 :5 by volume).
  • TTIP 5 Aldrich >97%) and vanadium oxo-triisopropoxide (Strem Chemicals, >98%) were added, resulting in total metal concentrations ranging from 0.1 to 3.4 (without solvent) mol L "1 with 10 wt.% V 2 O 5 content in the resulting powder product.
  • TTIP 5 Aldrich >97%)
  • vanadium oxo-triisopropoxide Stringem Chemicals, >98%)
  • FSP Flame spray synthesis
  • the vanadia/titania mixed oxides were synthesized by flame spray pyrolysis (FSP) in a laboratory-scale reactor.
  • the dispersion gas O 2 , Pan Gas, 99.95%) was added (Fig. 1).
  • the area of the annular gap (maximum 0.25 mm 2 ) was adjusted to achieve a pressure drop of 1.5 bar of the dispersion gas.
  • the precursor solution was fed by a 5 syringe pump (Inotec, IER-560) into the flame through the innermost capillary, where it was dispersed by a defined O 2 flow (5 L min "1 ) through the 1 st annulus.
  • the spray was ignited by a circular premixed flame (inner diameter 6 mm, slit width 10 ⁇ m) of CH 4 (1.5 L min "1 , Pan Gas 99.5%) and O 2 (3.2 L min "1 ).
  • An additional O 2 sheath (5 L min "1 ) to guarantee total combustion of the precursor was supplied through a ring 0 of sintermetal (inner/outer diameter 11/18 mm).
  • AU gas-flow rates were adjusted by calibrated mass-flow controllers (Bronkhorst).
  • the powders were collected on a glass microfibre filter (Whatman GFfD 257 mm in diameter), by sucking the gas-flow through the filter by a downstream installed vacuum pump (Busch SV 1025 B).
  • the production rate (g(V 2 0 5 /Ti0 2 ) h "1 ) was adjusted via the metal concentration in the liquid precursor.
  • the o ceramic foams (Vesuvius, mullite, Al 6 O 1S Si 2 , 20 pores per inch (ppi); porosity 0.85) used, exhibited a diameter of 15 mm and a length of 50 mm.
  • the foam support was wrapped into a glass fiber tape (Horst, GB25) before installation.
  • the unloaded weight of the foams were determined (Mettler s Toledo, AB204S) before coating.
  • One uncoated foam was installed in the deposition zone, build out and weighed. This sequence was repeated three times with no indication of loosing foam mass. All FSP- made catalysts were coated with a comparable mass OfV 2 O 5 ZTiO 2 (21 to 27 mg).
  • a wet-phase made 7 and 10 wt.% vanadia/titania catalyst was prepared by precipitation method, dried and then crushed to obtain the desired particle fraction size.
  • flame made vanadia/titania was pelletized (70 MPa) and 5 crushed in order to get a split fraction in the same particle size fraction as the wet- phase reference catalyst size.
  • the pressed flame-made catalyst is later described as FSP-made split.
  • the wet-phase made reference was calcined for 1 hour at 450°C, a common production step for wet-phase made catalyst preparation [16] to ensure the evaporation of precursor residuals.
  • Specific surface areas Specific surface areas (SSA, m 2 g "1 ) of the powders were determined from the adsorption of nitrogen (Pan Gas, >99.999%) at 77 K using the Brunauer-Emmett-Teller (BET) method with a Microraeritics Tristar 3000 (five point-isotherm, O.O5 ⁇ p/po ⁇ O.25). Assuming spherical, monodisperse primary particles with homogenous density, the average BET-equivalent particle diameter (d BET ) was calculated with equation(l).
  • BET Brunauer-Emmett-Teller
  • TPR Temperature programmed reduction
  • Raman spectroscopy Raman spectroscopy for the sinter study and 3 o identifying different vanadia species on the titania was done with a Renishaw InVia Reflex Raman system equipped with a 785 nm diode (solid state, 300 mW) laser as excitation source. Samples were focused by a microscope (Leica, magnification x50). The spectra were recorded on a CCD camera after diffraction (1200 lines per millimeter) at reduced laser energy of 0.3 mW to ensure no thermal change of the sample by excitation with the laser beam [21]. Exposure time was 30s by 3 accumulations for all scans.
  • Transmission and scanning electron microscopy In order to carry out transmission electron microscopy (TEM) investigation, the material was deposited onto a carbon foil supported by a copper grid. TEM analysis was performed with a o CM30ST microscope (Philips; LaB6 cathode, operated at 300 IcV, point resolution ⁇ 2A). SEM analysis was carried out on a Leo 1530 Gemini microscope (Zeiss, operated at 2 kV field emission gun).
  • Reactor for catalytic experiments 5
  • the catalysts were tested in the partial oxidation of o-xylene using a fixed bed plug flow reactor. It consists of a gas feed section with supply of o-xylene, the reactor and the product analysis by means of gas chromatography.
  • Pressure control The pressure in the reactor was indicated by a manometer 5 and adjusted by a manual needle valve downstream to the reactor. In order to assure a stationary evaporation of the o-xylene, the pressure in the evaporation zone was adjustable by a manual needle valve. Both, the pressures in the reactor and in the evaporation zone were kept constant during the experiments.
  • O-xylene was fed via a ⁇ -flow controller (Bronkhorst).
  • the nitrogen was then added to the liquid flow.
  • the reactor consisted of a vertically installed stainless steel tube of 16 mm inner diameter and a length of 380 mm, electrically heated.
  • the reactor, parts of the feed pipes, and the 6 port valve were in housed a glass wool isolated box heated electrically to 26O 0 C to support isothermal conditions throughout the reaction zone and prevent condensation.
  • the gas-flow enters the reactor from the top.
  • the fixed bed consists of three o zones.
  • Initial break-in zone (length ⁇ 120 mm). It consists of either SiC particles (particle size 1 mm) or SiC particles and an additional uncoated foam for the test of the foam catalysts. In this zone, the desired plug flow regime develops and the reactant gas-flow is heated. 5 2. Catalyst zone (length ⁇ 120 mm); either particles (wet-phase or FSP-made split catalyst, diluted in SiC, 1 mm) or of coated ceramic foams. The coated foams were installed in the isothermal zone of the reactor in the same orientation with respect to gas flow direction as they were coated before with FSP.
  • thermowell inner diameter 1 mm located at the radial center of the reactor tube.
  • a thermocouple inserted in the thermowell measured the 5 temperature along the catalyst bed.
  • the reactant gas flow can be piped through either the bypass or the reactor.
  • GC Gas analysis
  • Afterburner and off-gas analysis The complete gas flow from the reactor outlet together with compressed air (800 niL min "1 ) is directed to a catalytic afterburner (CAB) coated with a spherical Al 2 O 3 supported Pd catalyst.
  • the CAB is o an electrically heated (450°C) tubular reactor with a length of 250 mm and an inner diameter of 20 mm.
  • the off-gas after the CAB was analyzed continuously by an infrared- detectors (Leybold-Haereus, Binosl) for of CO and CO 2 .
  • the CAB was bypassed to determine the amount of CO and CO 2 5 produced during reaction.
  • the total volume gas-flows of the outlet were varied between 120 and 600 mL min "1 in order to adjust different residence times.
  • the mass of the active component in the reactor ranged from 15 to 45 mg in case of the FSP made catalysts and from 0.5 to 1.5 g in case of the wet-phase made catalysts.
  • Temperature 5 measurements inside the catalytic bed showed constant temperatures throughout the fixed bed around 366 0 C ⁇ 1°C. Therefore, isothermal conditions for both, FSP-made and wet-phase made reference catalysts, were assumed.
  • the data reported refer to average values calculated from 4 to 6 analyses at steady state conditions. 0
  • Figure 3 shows the dependence of specific surface area (SSA) of flame-made vanadia/titania on the production rate.
  • SSA specific surface area
  • the liquid feed rate and the dispersion gas feed rate was kept constant during experiments.
  • the SSA (squares) of the powders decreases with increasing the total metal concentration in the precursor solution, which is consistent with the results of other studies on mixed metal oxides produced by flame spray pyrolysis [22, 23].
  • Higher combustion enthalpy densities and high titania concentrations favor the agglomeration and coalescence of the particles in the gas- phase, reducing the overall specific surface area [24].
  • the active component exhibits 195 m 2 g "1 SSA. This decreases with increasing precursor concentration until it approaches a constant value at
  • the anatase crystal size increased with increasing production rate from s 10 nm up to 32 nm. Crystal sizes (diamonds) correspond very well to calculated d ⁇ ET (circles), which are slightly below. Small deviation between d ⁇ ET and anatase crystal size are due to the simpUfying assumptions made in the calculation of the d ⁇ ET - For 2.6 g(V2 ⁇ 5/TiO 2 ) h "1 production rate the lowest anatase content of 82 wt.% was found. For production rates above 17 g(V 2 0s/Ti0 2 ) h '1 > 94 wt.% anatase content 0 were obtained.
  • the FSP-made as prepared vanadia/titania shows an almost pure anatase crystal phase (> 94 wt.%) and no evidence of any vanadia crystal structure.
  • Figure 5 shows TEM (a) and SEM (b) images of primary particles of the wet-phase catalyst.
  • Primary particles are non-spherical and sizes are mainly above 100 nm.
  • Electron diffraction analysis shows the crystalline structure of the particles.
  • the SEM image shows the calcined split fraction of the wet-phase made V 2 O 5 ZTiO 2 (0.244 to 0.5 mm) as it was used for the catalytic test.
  • Sieved split agglomerates consist of many primary particles with no or slight indication of sintering.
  • Pore size distribution The pore size distributions of different powders are shown in Figure 6.
  • the production rate has almost no significant influence on the pore size distribution of the flame-made V 2 0s/Ti0 2 for SSAs ranging from small (89 g(V 2 0 5 /Ti0 2 ) h '1 ) to high (17 g(V 2 0 5 /Ti0 2 ) h '1 ) (a).
  • Pressing FSP-made particles into a split resulted in smaller pores (10 to 30 nm) than for the untreated powder (20 to 110 nm). During the split preparation, particles were packed closely to each other thereby reducing the average pore size.
  • the wet-phase made V 2 CVTiO 2 exhibited pore sizes ranging from 20 to 160 nm lying in the range of the wet-phase made particle size, therefore representing the interparticle voids.
  • An open pore o structure is favored for this reaction that is inner mass transfer limited.
  • FSP-made vanadia/titania ( ⁇ 600°C) had a monolayer (ML) coverage below 3 (Table 1), and showed therefore only one distinct reduction peak [27].
  • Particles 5 sintered at 65O 0 C had a ML coverage of 23, resulting in a distinct peak around 650 0 C and the onset of a second peak ranging from 700 to 800 0 C.
  • m contrast the wet-phase reference with ML coverage of over 4 has two distinct peaks at 525°C and 843 0 C as was expected [27].
  • T max ⁇ 540 0 C rather polymeric
  • T max > 580 0 C monomeric vanadia o species
  • the vanadia species was stable on the titania up to 450 0 C sinter temperature. o
  • the SSA retained constant up to 45O 0 C.
  • Increasing the sinter temperature from 450 up to 900°C resulted in a steep decrease of the SSA from 83 m 2 g "1 to 0.5 m 2 g "1 .
  • the dramatic decrease in the SSA corresponds to transformation of titania crystal structures and restructuring of vanadia species. Vanadia, being liquid above 670 0 C 3 may have acted as flow agent during titania sintering. 5
  • the wet-phase made shows only crystalline vanadia bands (708 cm “1 and 994 cm “1 ) [34, 35].
  • FIG. 7 shows images of an uncoated (a) and two coated foams (b,c). Arrows indicate the gas-flow direction during deposition.
  • Figure 7 b shows a foam that was coated with a constant pressure drop over the foam and the filter of 80 mbar.
  • the V 2 O 5 ZTiO 2 particles are almost evenly distributed on the foam surface. At these production conditions, the gas-flow through the foam is very slow so that particles deposited mainly by diffusion and thermophoretic sampling. This type of coating will be referred to as "high" dispersion 5 later on.
  • Figure 7 c shows a foam where particles were deposited at a constant throttle position (50%) resulting in a pressure drop of 200 to 300 mbar over the filter and foam. Deposition in this case is caused mainly by impaction resulting from the high gas-flow velocities. The vanadiaZtitania is dominantly deposited on support surfaces o facing against the particle laden gas flow, resulting in a patchy coating, to which will be referred later on as "low" dispersion.
  • Coating thickness for this deposition condition is in the micrometer range, as demonstrated in the SEM images ( Figure 8) of the cross-section of the coated foam.
  • the deposited V 2 CVTiO 2 was 50 mg resulting in a layer thickness of 150 to 200 ⁇ m. Particle layer is not uniform and rough, a highly porous layer is observed.
  • Recently direct deposited, FSP-made nano particles on flat surfaces resulted porosities of the deposited layer around 98% [3]. Comparable particle sizes and production conditions during the vanadia/titania production may lead to similar porosities.
  • Coated foams showed higher activity than splits made out of flame-made V 2 CVTiO 2 or wet-phase made V 2 O 5 /TiO 2 .
  • flame-made V 2 (VTiO 2 provides more external surface area than the wet-phase made V 2 O 5 ZTiO 2 .
  • the high SSA and the monomelic vanadia species on titania result in higher catalytic activity compared to the wet-phase made catalyst.
  • the FSP-made split showed slightly lower activity than the direct deposited foams.
  • a slightly lower SSA (Table 1) and smaller pore sizes and longer diffusion ways inside the catalysts grain may have led to or even increased inner mass transfer limitations decreasing the activity of the catalyst compared to the coated foams.
  • the low dispersion coating showed higher activity compared to the high dispersion coated foam. Differences between the "low” and “high” dispersion catalysts with high SSA may result from non iso-thermal conditions in the low dispersion coating.
  • the low selectivity of the FSP-made split may be explained by the mass transfer limitations.
  • O-xylene reacts to phthalic anhydride inside the small pores of the catalyst grain ( Figure 6) being trapped inside the grain resulting oxidation of PA. Therefore large amounts of CO and CO 2 were produced..
  • the coated foams no indications of inner mass transfer limitations were observed, resulting in a increasing selectivity with increasing o-xylene conversion until the selectivity collapses at conversions > 99 %.
  • Cs-doped active component was produced under the same conditions as were the high SSA (93 m 2 g "1 ) sample.
  • Production rate was 17 g(V 2 0 5 /Cs 2 0 /TiO 2 ) h "1 , nominal vanadia content 10 wt.%, pressure drop behind filter was adjusted to 80 mbar.
  • Anatase content was > 94 wt.%. No evidence of Cs 2 O crystals were found.
  • TPR showed higher T max (503 0 C) compared to the not doped V 2 O 5 /TiO 2 (Table 4).
  • TEM analysis showed mainly spherical particles. Absence of any particle in o micrometer range corroborates a monomodal particle distribution. Rings in the electron diffraction indicate clearly a crystalline structure.
  • the appendix provides additional information on calculations and results obtained in the experiments.
  • n i Kth a ne - ⁇ ⁇ (3) ethane

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Abstract

L'invention porte sur un procédé de production d'un catalyseur consistant: à déposer à sec un matériau catalytique actif en suspension dans un gaz sur un support poreux, ledit matériau catalytique actif présentant une surface active comprise entre 0,3 et 1000m2/g. L'invention porte également sur les catalyseurs ainsi obtenus et sur leur utilisation dans des réactions chimiques.
PCT/CH2006/000338 2005-06-29 2006-06-22 Procede de fabrication d'un materiau catalytique actif Ceased WO2007000068A1 (fr)

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DE102008053554A1 (de) 2008-10-28 2010-04-29 Behr Gmbh & Co. Kg Klimasystem für ein Gebäude
WO2011045051A1 (fr) * 2009-10-13 2011-04-21 Süd-Chemie AG Système de réacteurs pour oxydation en phase gazeuse catalytique
CN114849743A (zh) * 2022-05-13 2022-08-05 西南石油大学 一种基于低共熔溶剂合成锐钛矿二氧化钛的方法

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JPS61232285A (ja) * 1985-04-04 1986-10-16 エヌオーケー株式会社 高強度軽量セラミツクス材料
EP0501003A1 (fr) * 1991-02-28 1992-09-02 Sakai Chemical Industry Co., Ltd., Catalyseur et méthode pour décomposer de l'ozone par son utilisation
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WO2003070640A1 (fr) * 2002-02-19 2003-08-28 Tal Materials Particules d'oxydes metalliques mixtes produites par pyrolyse avec projection a la flamme d'une charge liquide de precurseurs d'oxyde dans des solvants oxygenes
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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102008053554A1 (de) 2008-10-28 2010-04-29 Behr Gmbh & Co. Kg Klimasystem für ein Gebäude
WO2011045051A1 (fr) * 2009-10-13 2011-04-21 Süd-Chemie AG Système de réacteurs pour oxydation en phase gazeuse catalytique
CN114849743A (zh) * 2022-05-13 2022-08-05 西南石油大学 一种基于低共熔溶剂合成锐钛矿二氧化钛的方法

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