[go: up one dir, main page]

WO2000071247A1 - Systemes equilibres de catalyseur au polyoxometalate a base de tungstene - Google Patents

Systemes equilibres de catalyseur au polyoxometalate a base de tungstene Download PDF

Info

Publication number
WO2000071247A1
WO2000071247A1 PCT/US2000/014511 US0014511W WO0071247A1 WO 2000071247 A1 WO2000071247 A1 WO 2000071247A1 US 0014511 W US0014511 W US 0014511W WO 0071247 A1 WO0071247 A1 WO 0071247A1
Authority
WO
WIPO (PCT)
Prior art keywords
solution
group
useful
main
electron
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/US2000/014511
Other languages
English (en)
Inventor
Richard S. Reiner
Elena M. G. Barbuzzi
Ira A. Weinstock
Craig L. Hill
Michael W. Wemple
Jennifer J. Cowan
Rajai H. Atalla
Robert A. Heintz
Alan J. Bailey
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Emory University
US Department of Agriculture USDA
Wisconsin Alumni Research Foundation
Original Assignee
Emory University
US Department of Agriculture USDA
Wisconsin Alumni Research Foundation
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Emory University, US Department of Agriculture USDA, Wisconsin Alumni Research Foundation filed Critical Emory University
Priority to AU52929/00A priority Critical patent/AU5292900A/en
Publication of WO2000071247A1 publication Critical patent/WO2000071247A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

Links

Classifications

    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
    • D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
    • D21C9/10—Bleaching ; Apparatus therefor
    • D21C9/1063—Bleaching ; Apparatus therefor with compounds not otherwise provided for, e.g. activated gases
    • 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
    • B01J23/24—Chromium, molybdenum or tungsten
    • B01J23/30—Tungsten
    • 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
    • B01J27/00—Catalysts comprising the elements or compounds of halogens, sulfur, selenium, tellurium, phosphorus or nitrogen; Catalysts comprising carbon compounds
    • B01J27/14—Phosphorus; Compounds thereof
    • B01J27/186—Phosphorus; Compounds thereof with arsenic, antimony, bismuth, vanadium, niobium, tantalum, polonium, chromium, molybdenum, tungsten, manganese, technetium or rhenium
    • B01J27/188—Phosphorus; Compounds thereof with arsenic, antimony, bismuth, vanadium, niobium, tantalum, polonium, chromium, molybdenum, tungsten, manganese, technetium or rhenium with chromium, molybdenum, tungsten or polonium

Definitions

  • thermodynamic instability In almost all cases, catalysts composed of transition- and main-group ions are prepared and isolated under conditions very different from those in which they are designed to operate. As a result, most catalysts are only kinetically, rather than thermodynamically, stable.
  • the catalysts, as prepared, lie far from thermodynamic equilibrium when placed in their operating environment, which can include solvents, additives, impurities, reactants, intermediates, products and byproducts under various conditions of temperature and pressure. The catalyst will gradually be converted into thermodynamic product(s) as the whole chemical system moves spontaneously toward equilibrium. What is more, this movement usually creates undesired changes in the catalyst itself.
  • thermodynamic instability is particularly applicable to soluble (homogeneous) catalysts as they generally will decompose at faster rates than their solid-state (heterogeneous) counterparts.
  • the process of homogeneous-catalyst degradation is often accelerated by the presence of water, which can react with transition-metal or main-group ions via hydrolysis or condensation reactions to give inactive metal oxides or hydroxides.
  • H + or OH " Reactions of cations or anions with water or with its components, H + or OH " , are referred to as speciation reactions. Catalysts and their components are also susceptible to speciation reactions. They possess useful kinetic stabilities in water over relatively narrow ranges of H + or OH " concentrations and are rapidly degraded when the pH deviates too greatly. There is a need to limit changes in H + and OH " concentrations (pH control) in the design of aqueous and other catalyst systems. For example, in aqueous systems, when eiectron-containing substrates are oxidized by electron acceptors (oxidants), the H + concentration of the solution generally increases linearly with the number of electrons transferred from substrate to oxidant (a drop in the pH of the solution).
  • OH " anions are generated (an increase in pH) when POM solutions are used as reducing agents in the presence of oxidants such as dioxygen (O 2 ), ozone (O 3 ), hydrogen peroxide (H 2 O 2 ) or other peroxides (i.e., oxidants that possess the 0 2 2" functionality).
  • oxidants such as dioxygen (O 2 ), ozone (O 3 ), hydrogen peroxide (H 2 O 2 ) or other peroxides (i.e., oxidants that possess the 0 2 2" functionality).
  • the substrate, the oxidizing or reducing agents or the desired product(s) are susceptible to decomposition by H + or OH " ions.
  • POMs for short
  • POMs are a large, structurally diverse and rapidly growing class of inorganic compounds. They are composed of d° metal cations, especially W(VI), Mo(VI) and V(V), linked to one another by oxide anions (O 2" ) in varying combinations.
  • Polvoxometalates in both of the classes may be mixed-addendum, meaning they contain more than one type of the d° metal cations.
  • Isopoiyanions have the general formula [M x O y ] n" ; examples include [W 7 O 24 ] 6" and [V 2 W 4 O 19 ] 4" .
  • Heteropolyanions have the general formula [X a M b OJ m" where X n+ is a heteroatom; examples include [Co" l W 12 O 40 ] 5" and [SiVMoW 10 O 40 ] 5" .
  • the negative charges of POMs can be counterbalanced by hydrophilic cations, such as H + , Li + , Na ⁇ K + , and NH 4 + , to provide neutral salts that are soluble in water.
  • POMs can range in size from 9A (0.9 nm) to over 3 ⁇ A (3 nm).
  • Heteropolyanions are a larger, more versatile, and more easily modified class of POMs than the isopoiyanions. The most common and most thoroughly investigated structure of heteropolyanions is the Keggin molecule (ca. 11 A) shown in Fig. 1.
  • POMs are being developed to catalyze a rapidly expanding library of chemical reactions. Many POM catalysts and catalyst systems have been developed as solid-state heterogeneous catalysts as well as a variety of homogeneous catalysts soluble in both water and organic solvents. Several attributes make POMs attractive for use in catalysis. First, POMs can be readily prepared in water from inexpensive, minimally toxic, and accessible compounds such as sodium tungstate (Na 2 WO 4 ), sodium molybdate (Na 2 MoO 4 ), sodium metavanadate (NaVO 3 ), sodium metasilicate (Na 2 SiO 3 ), and phosphoric acid (H 3 PO 4 ).
  • sodium tungstate Na 2 WO 4
  • Na 2 MoO 4 sodium molybdate
  • NaVO 3 sodium metavanadate
  • Na 2 SiO 3 sodium metasilicate
  • H 3 PO 4 phosphoric acid
  • POMs can be reversibly reduced, often by many electrons, while being simultaneously resistant to oxidative degradation.
  • Such d° systems which include common materials like sand, glass, and many ceramics, are already in the maximum oxidation state attainable under any conventional reaction conditions.
  • POMs exhibit a tremendous amount of flexibility as a number of key physical properties, such as redox potential, acidity, charge, solubility, etc., can be controlled to a marked degree by rational design and synthesis.
  • One or more of the d° metal ions in the parent POM structure can be replaced by d- electron-containing metal ions or by main-group cations. Indeed, the profound control of the chemically significant properties of POMs vests, in part, in this rich substitution chemistry.
  • conjugate- base anions can lead to operational problems associated with such impurities, such as corrosion of reactor walls and interference with the chemical operations of the catalyst.
  • removal of the salts of the conjugate-base anions often involves laborious extractions with organic solvents or crystallizations, both of which add to the equipment, labor and material costs of the synthetic procedures.
  • This goal would be achieved by preparing equilibrated POM-catalyst systems in a single step from component-element precursors.
  • POMs and their associated cations are also susceptible to speciation reactions. Although many POMs are remarkably resistant to oxidative degradation, and thus excellent candidates for use as oxidation catalysts, they possess useful kinetic stabilities in water over relatively narrow ranges of H + or OH " concentrations. Thus, most well- defined isopoly- or heteropolyoxometalates are rapidly degraded when used at the conditions often desired for catalysis, namely temperatures of 100°C or greater and neutral pH values. As is the case with most metal-based catalysts, thermodynamic instability severely limits their usefulness in water. To overcome this limitation, it would be desirable to prepare soluble POM- catalysts that are thermodynamically stable with respect to undesired speciation reactions in water and which are additionally capable of buffering their own reactions.
  • heteropolyoxomolybdate solutions are restricted to acidic conditions which may be undesirable for many chemical systems.
  • An additional obstacle to their more expanded use in catalysis is that the substitution chemistry of heteropolyoxomolybdates is very limited.
  • Heteropolyoxotungstates constitute a much more diverse class of soluble POM catalysts. Because they are generally less labile (i.e., more kinetically stable) than similar molybdate-based anions, it is easier to isolate a greater variety of tungsten-based POM compounds. Isopoly and heteropolyoxotungstates have been synthesized using a broader range of conditions than have the isopoly- or heteropolyoxomolybdates.
  • heteropolytungstates are stable ranges from strongly acidic to weakly basic conditions for a vast array of d-electron-containing transition- metal-substituted and other derivatives.
  • catalysts from these classes of polytungstates complexes have only been isolated as kinetically-stable products which are thermodynamically unstable under the conditions at which they are used. They are susceptible to decomposition in water when heated to elevated temperatures or after prolonged use. Therefore, in order to greatly expand the application of POMs as catalysts, it is necessary that thermodynamically (i.e., inherently) stable tungsten-based soluble polyoxometalate-catalyst systems be developed.
  • thermodynamically stable systems and to additionally incorporate a capacity for self-buffering is to prepare soluble tungsten-based polyoxometalate catalysts from principal components as thermally equilibrated mixtures.
  • thermally equilibrated mixtures there was no reason to expect that useful equilibrated tungsten-based POM mixtures could be obtained or predictably modified. Indeed, the available kinetic data suggested otherwise.
  • equilibrated mixtures of heteropolyoxomolybdates can be prepared under mild conditions.
  • the kinetic barriers to attaining thermodynamic equilibria between polyoxomolybdates in aqueous solution are relatively small, much smaller than the kinetic barriers to attaining equilibria between polyoxotungstates.
  • Half-lives for the equilibration of polyoxomolybdates are on the order of seconds to minutes in contrast to half-lives for polyoxotungstates which range from days to months. Such differences mean that polyoxomolybdates are orders of magnitude more labile than most polyoxotungstates. Consequently, while equilibrium mixtures of polyoxomolybdates could be readily prepared from metal-oxide precursors, no such expectations for equilibrated tungsten-based POM mixtures prepared by similar methods exist. It might have been argued that if sufficiently high temperatures were used, the approach to thermodynamic equilibrium would be more rapid.
  • the present invention is a homogeneous solution that contains one or more desired or useful (target) tungsten-based isopoly- or heteropolyoxometalate (POM) complexes present in equilibrium with all chemical species related to the complex or complexes by reactions between chemical components of the system.
  • target tungsten-based isopoly- or heteropolyoxometalate
  • This solution comprises various soluble compounds that contribute specific whole-number or fractional ratios of any or all of the elements V, Nb, Ta, Mo, W, d-electron-containing transition-metal ions (TM) and main-group ions (MG) such that there exists one or more target polyoxometalates of the general formula [V k Nb rn Ta n Mo 0 W p (TM) q (MG) r OJ 2' where TM is a d-electron-containing transition-metal ion and MG is a main- group ion; k is 0-18, m is 0-20, n is 0-10, o is 0-19, p is 1-150, q is 0-9 and r is 0-9; k ⁇ p, m ⁇ p, n ⁇ p and o ⁇ p provided that p > 1 and k + m + n + o + p > 4; and s is sufficiently large that
  • One specific embodiment of the present invention is an equilibrated, homogeneous solution containing target tungsten-based complexes that contain relatively high molar ratios of tungsten to molybdenum. Another specific embodiment of the present invention is an equilibrated, homogeneous solution containing target tungsten-based complexes that contain molar ratios of tungsten to molybdenum greater than five to one. Another specific embodiment of the present invention is an equilibrated, homogeneous solution containing target tungsten-based complexes that contain molar ratios of tungsten to molybdenum greater than four to one.
  • Another specific embodiment of the present invention is an equilibrated, homogeneous solution containing target tungsten-based complexes that contain molar ratios of tungsten to molybdenum greater than three to one.
  • Another specific embodiment of the present invention is an equilibrated, homogeneous solution containing target tungsten-based complexes that contain molar ratios of tungsten to molybdenum greater than two to one.
  • Another specific embodiment of the present invention is an equilibrated, homogeneous solution containing target tungsten-based complexes that contain molar ratios of tungsten to molybdenum greater than one to one.
  • a preferred method for preparing the solutions of the present invention is to mix hydroxides or neutral or anionic oxides of transition-metal or main- group elements in water and to heat the mixtures to temperatures sufficiently high such that the hydroxides or neutral or anionic oxides of the transition- metal or main-group elements react to give the target polyoxotungstates of the general formula in thermodynamic equilibrium with additional chemical species or complexes also derived from the hydroxides or neutral or anionic oxides of the transition-metal or main-group elements.
  • the present invention is a method of using a homogeneous, aqueous solution, comprising one or more catalytically or otherwise useful tungsten-based isopoly- or heteropolyoxometalate (POM) complexes present in thermal equilibrium for homogeneous or heterogenous oxidation of an organic or inorganic chemical substrate.
  • POM catalytically or otherwise useful tungsten-based isopoly- or heteropolyoxometalate
  • One particularly advantageous application of this method is the application of the polyoxometalate solution in the present invention to wood pulp, wood fiber, lignocellulosic pulp or lignocellulosic fiber such that enhanced delignification occurs.
  • the present invention is a method of preparing a self-buffering system, comprising preparing a homogeneous, aqueous buffer solution, comprising one or more tungsten-based isopoly- or heteropolyoxometalate (POM) complexes present in thermal equilibrium with all other related chemical species by reactions between chemical components of the system
  • the system pH is maintained within a pH range of 4 units, preferably 2 units and most preferably 1 unit
  • the buffer consists of various soluble compounds that contribute specific whole-number or fractional ratios of any or all of the elements V, Nb, Ta, Mo, W, d-electron-containing transition-metal ions (TM) and main-group ions (MG) such that there exists one or more useful polvoxometalates of the general formula [V k Nb m Ta n Mo 0 W p (TM) q (MG) r O s ] z where TM is a d-electron-containing transition-metal ion and
  • ratios of the elements used can be modified along a continuum of compositions such that the resulting polyoxometalate mixture can be adjusted to control the pH of the prepared solution and the pH at which the solution acts as a pH buffer via changes in the relative concentrations of species present in the equilibrium mixture.
  • ratios of the elements used can be modified along a continuum of values such that the concentrations of target heteropolyoxotungstates of the general formula along with other species present in the equilibrated polyoxometalate mixture can be adjusted to optimize the physical and chemical properties of the system for use in particular applications.
  • Another advantage of the present invention is to isolate target polyoxotungstates of the general formula from a polyoxometalate solution that was prepared by mixing of hydroxides or neutral or anionic oxides of transition-metal or main-group elements in water and heating the mixtures at temperatures sufficiently high such that the hydroxide or neutral or anionic oxide precursors of transition-metal or main-group elements react to give the target polyoxotungstates of the general formula.
  • An objective of the present invention is to delignify hardwood or softwood fibers, hardwood or softwood pulps, or fibers or pulps from other lignocellulosic materials using suitable equilibrated polyoxotungstate solutions.
  • Another objective of the present invention is to oxidize carbon monoxide (CO) to carbon dioxide (CO 2 ) using suitable equilibrated polyoxotungstate solutions.
  • Another objective of the present invention is to oxidize reducing agents using suitable equilibrated polyoxotungstate solutions.
  • a feature of the present invention is that suitable equilibrated polyoxotungstate solutions may be reoxidized with an oxidant selected from the group consisting of air, oxygen, hydrogen peroxide and other organic or inorganic peroxides (free acid or salt forms), or ozone.
  • an oxidant selected from the group consisting of air, oxygen, hydrogen peroxide and other organic or inorganic peroxides (free acid or salt forms), or ozone.
  • equilibrated polyoxotungstate solutions may be oxidized using suitable oxidants.
  • transition metals may be incorporated into the equilibrated polyoxotungstate solutions to increase the rates of reoxidation using an oxidant selected from the group consisting of air, oxygen, hydrogen peroxide and other organic or inorganic peroxides (free acid or salt forms), and ozone.
  • equilibrated polyoxotungstate solutions may be used as an oxidant and be reoxidized in repeated cycles.
  • Another feature of the present invention is that suitable equilibrated polyoxotungstate solutions may be used wherein polyoxometalate complexes are reduced and reoxidized within the same process step.
  • Fig. 1 A disubstituted, ⁇ -Keggin heteropolyanion displayed in polyhedral notation.
  • Each polyhedron represents a main-group or transition- metal atom at its center with oxygen atoms at each of its vertices.
  • the black tetrahedron in the center represents the oxide of the heteroatom
  • the ten gray octahedra represent the oxides of the structural atoms
  • the two white octahedra represent oxides of the substituted atoms.
  • This figure represents one of the possible positional isomers of the [SiV 2 W 10 O 40 ] 6' anion.
  • Fig. 2. 51 V NMR spectrum of K 9 [SiVW 10 O 39 ]-14H 2 O in D 2 O (pD 8.4) prepared in a stepwise manner (Example 1a) after treatment with excess LiCIO 4 and removal of precipitated KCIO 4 .
  • Fig. 3. 51 V NMR spectrum of K 6 [SiV 2 W 10 O 40 ] » xH 2 O in D 2 0 (pD 4.1 ) prepared in a stepwise manner (Example 1 b). The peaks shown represent different positional isomers of the [SiV 2 W 10 O 40 ] 6" anion.
  • Fig. 5 51 V NMR spectrum of a 0.1 M Na 6(+2) [SiV 2 W 10 O 40 ] solution prepared as an equilibrium mixture from the neutral and anionic elemental oxides (Example 3a); elemental bromine was added to the NMR sample to ensure full oxidation. Peaks labeled (1 ) are isomers of [SiV 2 W 10 O 40 ] 6" ; the peak labeled (2) is [V 2 W 4 O 19 ] 4" present as part of the equilibrium mixture.
  • Fig. 6 51 V NMR spectrum of a 0.1 M Na 6(+2) [SiV 2 W 10 O 40 ] solution prepared as an equilibrium mixture from the neutral and anionic elemental oxides under mild reaction conditions (Example 3b); elemental bromine was added to the NMR sample to ensure full oxidation.
  • Fig. 7 51 V NMR spectrum of a 0.2 M Na 6(+2) [SiV 2 W 10 O 40 ] solution prepared as an equilibrium mixture from the neutral and anionic elemental oxides (Example 3c); elemental bromine was added to the NMR sample to ensure full oxidation.
  • Fig. 8 51 V NMR spectrum of a 0.5 M Na 6(+2) [SiV 2 W 10 O 40 ] solution prepared as an equilibrium mixture from the neutral and anionic elemental oxides (Example 3d); elemental bromine was added to the NMR sample to ensure full oxidation.
  • Fig. 9 51 V NMR spectrum of a K 6 [SiV 2 W 10 O 40 ] solution isolated from a equilibrium mixture prepared using neutral and anionic elemental oxides (Example 4). The sample was first oxidized using elemental bromine.
  • Fig. 10 Stacked 51 V NMR spectra of 0.1 M Na 6(+x) [SiV 2 W 10 O 40 ] solutions prepared from the elemental oxides with various stoichiometries of Na 2 WO 4 relative to WO 3 (Experiments A-D in Table 2 of Example 5); elemental bromine was added to each NMR sample to ensure full oxidation.
  • Fig 1 Equilibrium solutions of Na 6(+2) [S ⁇ V 2 W 10 O 40 ] and Na 6(+3) [S ⁇ V 2 W 10 O 40 ] titrated with acid at 70°C demonstrating differences in buffering capacity The horizontal plateaus indicate the buffering regions The dashed line is the pH if the acid had been added directly to water Fig. 12 Stability, as monitored by 51 V NMR, of a 0.1 M
  • Fig. 13 Stability of a 0.1 M Na 6(+2) [SiV 2 W 10 O 40 ] equilibrium solution used in several cycles of reduction by wood pulp followed by reoxidation by oxygen (O 2 ) (Example 7). The stability of the equilibrium system is emphasized by the constant pH maintained throughout the bleaching and reoxidation steps.
  • Fig. 14 51 V NMR spectrum of a 0.25 M Na 6 [AIVW 11 O 40 ] equilibrium solution, pH 3.9, prepared using neutral and anionic elemental oxides and hydroxides (Example 10b); elemental bromine was added to the NMR sample to ensure full oxidation. Peaks labeled (1 ) are isomers of [AIVW ⁇ O ⁇ ] 6" ; the peaks labeled (2), (3) and (4) are [V 2 W 4 O 19 ] 4" , [V 3 W 3 O 19 ] 5 and [HV 3 W 3 O 19 ] 4" , respectively, present as part of the equilibrium mixture.
  • Fig. 15 5 V NMR spectrum of a 0.25 M Na ⁇ .AIVWnO ⁇ equilibrium solution at pH 8.6 prepared using neutral and anionic elemental oxides and hydroxides (Example 10c); elemental bromine was added to the NMR sample to ensure full oxidation. Peaks labeled (1 ) are isomers of [AIVW 11 O 40 ] 6" ; the peaks labeled (2) and (3) are isomers of [V 2 W 4 O 19 ] 4" present as part of the equilibrium mixture. Fig. 16.
  • Fig. 17 Stability, as monitored by 51 V NMR of a 0.5 M Na 6(+1 5) [AI 1(+05) VW 11(+1) O 40 ] equilibrium solution used in several cycles of reduction by wood pulp followed by reoxidation by oxygen (0 2 ) (Example 13): (A) sample after initial synthesis, (B) after the first bleaching step, (C) after the first wet-oxidation/reoxidation step, (D) after the second bleaching step and (E) after the second wet-oxidation/reoxidation step. Elemental bromine was added to the NMR sample to ensure full oxidation.
  • Fig. 18 Stability of a 0.1 M Na 6(+1 5) [AI 1(+05) VW 11(+1) O 40 ] equilibrium solution used in several cycles of reduction by carbon monoxide (CO) followed by reoxidation by oxygen (O 2 ) (Example 14). The stability of the equilibrium system is emphasized by the constant pH maintained throughout the reduction and reoxidation steps.
  • Fig. 19 51 V NMR spectrum of a 0.5 M Na 5(+1) [PV 2 W 10 O 40 ] solution prepared as an equilibrium mixture from the neutral and anionic elemental oxides (Example 15); elemental bromine was added to the NMR sample to ensure full oxidation. Peaks labeled (1 ) are isomers of [PV 2 W 10 O 40 ] 5" , peaks labeled (2) are isomers of [PV 3 W 9 O 40 ] 6' and the peak labeled (3) is [PWnOgg] 7" or [PW 10 O 36 ] 7" all present as part of the equilibrium mixture.
  • the peak labeled (1 ) is [SiVW ⁇ O ⁇ ] 5"
  • peaks labeled (2) are isomers of [SiV 2 W 10 O 40 ] 5"
  • the peak labeled (3) is [V 2 W 4 0 19 ] 4" present as part of the equilibrium mixture.
  • Fig. 22 Comparison the visible spectra of a Na 5(+ o .26) [SiMn 1( . 02) (H 2 O)W 11 O 39 ] equilibrium solution prepared using neutral and anionic elemental oxides and hydroxides (Example 22) to a literature "step-wise" preparation of K 5 [SiMn" l W 11 O 39 ].
  • the present invention is a homogeneous solution that comprises one or more catalytically or otherwise useful tungsten-based isopoly- or heteropolyoxometalate (POM) complexes present at in thermal equilibrium with all chemical species related to the useful complex or complexes by reactions between chemical components of the system.
  • POM isopoly- or heteropolyoxometalate
  • This solution comprises various soluble compounds that contribute specific whole-number or fractional ratios of any or all of the elements V, Nb, Ta, Mo, W, d-electron- containing transition-metal ions (TM) and main-group ions (MG) such that there exists one or more useful polyoxometalates of the general formula [V k Nb m Ta n Mo 0 W p (TM) q (MG) r O s ] z" where TM is a d-electron-containing transition-metal ion and MG is a main-group ion; k is 0-18, m is 0-10, n is 0-10, o is 0-19, p is 1-150, q is 0-9 and r is 0-9; k ⁇ p, m ⁇ p, n ⁇ p and o ⁇ p provided that p > 1 and k + m + n + o + p > 4; and s is
  • the homogeneous solutions of the present invention contain target POMs present as part of equilibrium distributions of chemically related species.
  • the target POM is one of eight different formulas that are subsets of the general formula.
  • the following equilibrated solutions 2-10 each comprise an example of such a target POM that is a subset of the general formula:
  • Equilibrated polyoxotungstate-catalyst solution 2 comprises a target isopolyoxotungstate or mixed-addendum isopolyoxotungstate present at a useful concentration as part of a homogeneous solution wherein it exists in thermal equilibrium with all chemical species present and related to one another and to the target isopoly- or mixed-addendum isopolyoxotungstate by reactions between chemical components of the system.
  • This solution comprises various soluble complexes that each contribute specific whole- number or fractional ratios of any or all of the elements V, Nb, Ta, Mo and W d-electron-containing transition-metal ions (TM) and main-group ions (MG) to the total chemical composition of the system such that there exists one or more useful isopolytungstate with the formula [V k Nb m Ta n Mo 0 W p O s ] z" where k ⁇ p, m ⁇ p, n ⁇ p and o ⁇ p provided that p ⁇ 1 and k + m + n + o + p > 4; and s is sufficiently large that z > 0.
  • the anions [W 10 O 32 ] 4" and [V 2 W 4 0 19 ] 4" are examples, respectively, of an isopolytungstate and of a mixed-addendum isopolytungstate of this formula.
  • Equilibrated polyoxotungstate-catalyst solution 3 comprises a target heteropolyoxotungstate possessing the Keggin structure present at a useful concentration as part of a homogeneous solution wherein it exists in thermal equilibrium with all chemical species present and related to one another and to the target heteropolyoxotungstate possessing the Keggin structure by reactions between chemical components of the system.
  • Equilibrated polyoxotungstate-catalyst solution 4 comprises a target transition-metal-bridged dimer of two tri-vacant Keggin heteropolyoxotungstate anions present at a useful concentration as part of a homogeneous solution wherein it exists in thermal equilibrium with all chemical species present and related to one another and to the target transition-metal-bridged dimer of two tri-vacant Keggin heteropolyoxotungstate anions by reactions between chemical components of the system.
  • Equilibrated polyoxotungstate-catalyst solution 5 comprises a target heteropolyoxotungstate with the Wells-Dawson structure present at a useful concentration as part of a homogeneous solution wherein it exists in thermal equilibrium with all chemical species present and related to one another and to the target heteropolyoxotungstate with the Wells-Dawson structure by reactions between chemical components of the system.
  • Equilibrated polyoxotungstate-catalyst solution 6 comprises a target transition-metal bridged dimer of two tri-vacant Wells-Dawson anions present at a useful concentration as part of a homogeneous solution wherein it exists in thermal equilibrium with all chemical species present and related to one another and to the target transition-metal bridged dimer of two tri-vacant Wells-Dawson anions by reactions between chemical components of the system.
  • This solution comprises various soluble complexes that each contribute specific whole-number or fractional ratios of any or all of the elements V, Nb, Ta, Mo and W d-electron-containing transition-metal ions (TM) and main-group ions (MG) to the total chemical composition of the system such that there exists one or more useful transition-metal bridged dimer of two tri-vacant Wells-Dawson anions with the formula
  • the anion [Zn 4 (H 2 O) 2 (P 2 W 15 O 56 ) 2 ] 16" is an example of a target transition-metal bridged dimer of two tri
  • Equilibrated polyoxotungstate-catalyst solution 7 comprises a target heteropolyoxotungstate possessing the Preyssler structure present at a useful concentration as part of a homogeneous solution wherein it exists in thermal equilibrium with all chemical species present and related to one another and to the target heteropolyoxotungstate possessing the Preyssler structure by reactions between chemical components of the system.
  • This solution comprises various soluble complexes that each contribute specific whole-number or fractional ratios of any or all of the elements V, Nb, Ta, Mo and W d-electron-containing transition-metal ions (TM) and main-group ions (MG) to the total chemical composition of the system such that there exists one or more useful heteropolyoxotungstate possessing the Preyssler structure with the formula [V k Nb m Ta ⁇ Mo 0 W p (TM) q (MG) r C,Os] z" where TM is a d-electron-containing transition-metal ion and MG is a main-group ion that is preferably P(V); C is a main-group ion or di- or tri-valent transition-metal or lanthanide ion located in the center of the structure that is preferably Na + ; k ⁇ p, m ⁇ p, n ⁇ p and o ⁇ p provided that i 1
  • Equilibrated polyoxotungstate-catalyst solution 8 a subset of equilibrated poiyoxotungstate-catalyst solution 3, comprises a target heteropolyoxotungstate possessing the Keggin structure present at a useful concentration as part of a homogeneous solution wherein it exists in thermal equilibrium with all chemical species related to the target heteropolyoxotungstate possessing the Keggin structure by reactions between chemical components of the system.
  • Target POM anions present in the equilibrated aqueous solutions used in the Examples include the sodium salts of [SiVW ⁇ O ⁇ ] 5" , [SiV 2 W 10 O 40 ] 6 ⁇
  • Equilibrated polyoxotungstate-catalyst solution 9 a subset of equilibrated poloxotungstate-catalyst solution 3, contains a target heteropolyoxotungstate possessing the Keggin structure present at a useful concentration as part of a homogenous solutions wherein it exists in thermal equilibrium with all chemical species related to the target heteropolyoxotungstate possessing the Keggin structure by reactions between chemical components of the system.
  • POM anions present in the equilibrated aqueous solutions used the Examples include the sodium salts of [SiMn(H 2 O)W 11 O 39 ] 5" and [AIMn(H 2 0)W 11 O 39 ] 6" .
  • the present invention is a solution comprising elemental ratios of ⁇ a:Si:V:Mn:Mo:W equal to 6.5:1.0.9:0.1 :1 :10.
  • the negative charges of POMs can be counterbalanced by cations which are components of and varied by careful selection of the starting compounds used in synthesizing the equilibrated solutions.
  • the degree of ion association is directed by the choice of solvent, cations and target and related POM anions and is dictated by the thermodynamic association constants commonly associated with anions and cations in solution.
  • Hydrophilic cations such as H + , Li + , Na + , K + , and NH 4 + , may be selected to provide acids (isopoly- or heteropolyacids) and/or salts (salts of isopoly- or heteropolyanions) that are soluble in water.
  • Ph 4 P + Ph 4 P +
  • the listed cations are sensible choices, but there are others available for particular applications.
  • an equilibrated solution may be referred to as Na 6(+2) [SiV 2 W 10 O 40 ]: the target POM anion of this solution is the sodium salt of the Keggin anion [SiV 2 W 10 O 40 ] 6" (i.e., Na 6 [SiV 2 W 10 O 40 ]), that exists as one component of the complex equilibrium mixture.
  • the solution contains two Na + ions (and two equivalents of HO " ) in excess of the six dictated by the empirical formula of the target POM. This excess is indicated by the subscripted "+2" in parentheses.
  • an equilibrated solution may be referred to as Na 6(+1 5) [AI 1(+05) VW 11(+1) O 40 ]: the target POM anion of this solution is the sodium salt of the Keggin anion [AIVW ⁇ O ⁇ ] 6' (i.e., Na AIVW ⁇ O ⁇ ]).
  • the solution contains 1.5 additional equivalents of Na + ions as indicated by the subscripted "(+1.5)", one-half an additional equivalent of Al(lll) ions as indicated by the subscripted "(+0.5)” and one additional equivalent of W(VI) ions as indicated by the subscripted "(+1 )”.
  • an equilibrated solution may be referred to as Na 5(+1 5) [SiV l(.0 1) (Mn 0 1 )MoW 10 O 40 ]: in this case the target POM salt is defined as Na 5 [SiVMo 0 W 11 - 0 O 40 ].
  • the solution contains 1.5 additional equivalents of Na + ions as indicated by the subscripted "(+1.5)", one-tenth of an equivalent less of V(V) than the number of equivalents dictated by the empirical formula (i.e., 0.1 equivalents less that the implied subscript of "1 " for V(V) in the formula) as indicated by the subscripted "(-0.1 )”.
  • this system contains one-tenth of an additional equivalent of Mn(ll or III) ion which is not necessarily incorporated into the target POM anion as indicated by the "(Mn ⁇ )". Because both equilibrated solutions as well as specific POM complexes will be described below, every effort will be made to differentiate clearly between equilibrated solutions (the present invention) and specific anions.
  • solution concentrations will be presented as if the solution contained only the target POM, although it is well understood that other species are present in the equilibrated solution.
  • Use of the herein described notation facilitates clear definition of the total concentrations of individual elements present in each equilibrated solution.
  • an equilibrated 0.5 M solution of Na 6(+1 5) [AI 1(+0 5) VW 11(+1) O 40 ] contains (in total): 3.75 M Na + , 0.75 M Al(lll), 0.5 M V(V) and 6 M W(VI) distributed over all the species present in the equilibrium solution.
  • the subscripted numbers associated with oxygen (O) atoms in the formulas used to describe the present inventions are limited to those defined by the empirical formulas of the target POMs — no subscripted parenthetical numbers are provided.
  • relative ratios of O 2" and HO " added directly to water in the preparation of these solutions are explicitly and fully defined by reference to the nature and relative molar ratios of the transition-metal and main-group oxides and hydroxides used as synthetic starting materials.
  • POMs of the present invention are most usefully prepared as described below in the Examples.
  • the present invention is a method for preparing the homogeneous, aqueous solutions that contain one or more catalytically or otherwise useful tungsten-based isopoly- or heteropolyoxometalate (POM) complexes present in thermal equilibrium.
  • the method comprises the steps of (a) mixing hydroxides or neutral or anionic oxides of transition- metal or main-group elements in water, and (b) heating such that the hydroxide or neutral or anionic oxide precursors of the transition-metal or main-group elements react to give the target polyoxotungstate anions of the general formula in thermodynamic equilibrium with additional chemical species or complexes also derived from the hydroxides or neutral or anionic oxides of the transition-metal or main-group elements.
  • the final solution will consist of various soluble compounds that contribute specific whole-number or fractional ratios of any or all of the elements V, Nb, Ta, Mo, W, d-electron- containing transition-metal ions (TM) and main-group ions (MG) such that there exists one or more useful polyoxometalates of the general formula [V k Nb rn Ta n Mo 0 W p (TM) q (MG) r O s ] z" where TM is a d-electron-containing transition-metal ion and MG is a main-group ion; k is 0-18, m is 0-10, n is 0-10, o is 0-19, p is 1-150, q is 0-9 and r is 0-9; k ⁇ p, m ⁇ p, n ⁇ p and o ⁇ p provided that p > 1 and k + m + n + o + p > 4;
  • the temperature of the mixture in the heating step is 50°C to 700°C.
  • the heating step is performed at a final pH of between 1.0 and 10.0, and the time of the heating step is between 0.1 and 24 hours.
  • the heating step takes place in a vessel capable of withstanding pressures exceeding the vapor pressure of the solution during the reaction plus any additional applied gaseous pressures.
  • the temperature of the mixture in the heating step is preferably 100°C to
  • the heating step is performed at a preferable final pH between 4.0 and 10.0, more preferably between 5.0 and 9.0.
  • the time of the heating step is preferably between 0.5 and 6.0 hours, most preferably between 1.0 and 3.0 hours.
  • the present invention namely a homogeneous solution that comprises useful tungsten-based POM complexes as part of a thermal equilibrium with related species, has a number of distinct advantages over other homogeneous catalysts. Advantages include ease of preparation, responsiveness to process perturbations and the ease with which physical and chemical properties can be rationally altered. Indeed, the existence and use of equilibrated homogeneous solutions of isopoly- and heteropolyoxotungstates described in the present invention provides additional degrees of freedom to an already flexible and systematically alterable class of compounds, thus dramatically increasing the scope of potential applications.
  • the thermally equilibrated tungsten-based POM solutions that constitute the present invention are preferably readily prepared from simple, component-element precursors as follows: Neutral transition-metal or main- group oxides or hydroxides, or salts consisting of cationic or anionic transition-metal or main-group oxides, hydroxides or aqua complexes and their counter-cations or -anions, that contribute specific whole-number or fractional ratios of any or all of the elements V, Nb, Ta, Mo, W, d-electron- containing transition-metal ions (TM) and main-group ions (MG), are mixed with or dissolved in water in either an open or sealed reactor and the resultant slurry or solution is heated with or without mechanical agitation under conditions of time, temperature and pressure such as are necessary to obtain a thermally equilibrated homogeneous solution that contains one or more useful polyoxometalates of the general formula.
  • an effective system may include several compositionally and structurally similar complexes that all perform equally well in a particular application.
  • an equilibrated solution may contain two target POM anions, such as [SiVMoW 10 O 40 ] 5" or [SiVMo 2 W 9 O 40 ] 5" .
  • each component element and their relative ratios are important factors in determining the nature, composition and concentration of each species present at equilibrium in the solution. Because many possible pathways exist by which identical equilibria may be reached, many equivalent options exist with regard to the choice of synthetic precursors. For example, if two equivalents of Na + and one equivalent of W(VI) are required, a single equivalent of Na 2 W0 4 might be used. Alternatively, one equivalent of WO 3 and two equivalents of NaOH might be used if they are less expensive or more readily available. The only difference between these two options is that in the latter case, one equivalent of water (H 2 0) is also included.
  • POMs themselves, such as sodium metatungstate (Na 6 [(H 2 )W 12 O 40 ]), are also suitable for use as precursor compounds.
  • POM solutions that require Na + and V(V) might be prepared using NaVO 3 or the combination of one-half an equivalent of V 2 O 5 with one equivalent of NaOH.
  • main-group heteroatoms such as Al(lll).
  • a single equivalent of AI(OH) 3 might be substituted by a combination of one-half equivalent of Al 2 0 3 and 1.5 equivalents of H 2 O.
  • the concentration of each species present is a function of the stoichiometric ratios of the cations and anions initially added and of the total volume and density of the solution.
  • sodium carbonate in water can be seen as sodium hydroxide and carbon dioxide (2NaOH*CO 2 ) where C0 2 is a gas that can be readily driven from the solution leaving the net addition of NaOH.
  • sodium acetate in water NaC 2 H 3 O 2 ⁇ 2 0
  • sodium hydroxide and acetic acid NaOH » HC 2 H 3 O 2
  • HC 2 H 3 O 2 is a volatile compound that can be readily evaporated from solution at the proper pH or extracted with organic solvent leaving the net addition of NaOH.
  • ion exchange could be used to obtain the net addition of NaOH.
  • water can be viewed as an ion pair consisting of hydrogen cations, H + , and hydroxide anions, OH "
  • a cation exchange resin where sodium ions, Na + , are associated with an insoluble, functionaiized polymer
  • the sodium resin is mixed with the solution, the H + and Na + exchange takes place and the solution and resin are once again separated.
  • the ion exchange resin will now have protons associated with the functionaiized groups on the polymer resin and the solution will now contain sodium cations, Na + , and hydroxide anions, OH " , or NaOH.
  • the reactor was pressurized with O 2 (2000 kPa) and heated to 200°C over the course of V 2 hour and held at this temperature for 3 hours with stirring to give 30 mL of a yellow-brown solution (final pH 8.20).
  • All the starting materials are simple oxides or salts of oxides that are relatively inexpensive and commercially available. While some of the starting materials are water-soluble compounds, namely Na 2 SiO 3 , NaVO 3 and Na 2 WO 4 *2H 2 O, others are essentially insoluble in water, W0 3 ⁇ 2 O.
  • the final color is an indication that there is a small amount of reduction in the final solution. This may be due to slight amounts of reduced compounds in the starting materials or by oxidation/reduction reactions taking place during the synthesis with impurities or the reactor walls. Syntheses done at lower temperatures have produced final solutions with no indication of reduction.
  • the purpose of oxygen over the solution is to help keep the POM solution in its most oxidized state during synthesis.
  • the 51 V NMR shown in Fig. 5 demonstrates that the [SiV 2 W 10 O 40 ] 6" anions are present as a component of the equilibrated Na 6(+2) [SiV 2 W 10 O 40 ] solution. This is clear when Fig. 5 is compared to Fig.
  • Fig. 5 shows that small amounts of isopoly- and heteropolyoxotungstates, such as [V 2 W 4 O 19 ] 4" , are present in equilibrium with the target POM anion.
  • a near-neutral (pH 6) aqueous solution of pure was prepared at room temperature.
  • the Keggin anion salt used to prepare this solution was prepared using traditional multi-step synthetic methods.
  • Wood pulp was then added to the solution and the mixture heated to 125°C.
  • 84% of the POM was reduced by lignin in the wood pulp; the final pH of the solution was 1.8.
  • the high H + concentration will lead to severe degradation of the cellulose in the pulp and drastically reduce the strength properties of the final paper product.
  • Equation 1 A new equilibrium distribution within the solution may be obtained by reversible condensation reactions that consume protons (Equation 1 ). Note that the species shown need only be present in small concentrations to consume a stoichiomet ⁇ cally large number of protons Conversely, addition of hydroxide (OH " ) might be compensated for by reversible hydrolysis reactions (Equation 2) [SiWnOag] 6" + [W0 4 ] 2" + 6 H + - [SiW 12 O 40 ] 4" + 3 H 2 0 (Eq. 1 )
  • Equation 4 The ability of an equilibrated solution to provide pH management is demonstrated by the following example involving the repeated reduction and reoxidation of equilibrated Na 6(+1 5) [AI 1(+05) VW 11(+1) O 40 ] using carbon monoxide (CO) as reducing agent and dioxygen (O 2 ) as oxidant.
  • the reactions were carried out separately as shown by Equations 4 and 5 below. Note the change in oxidation state of the vanadium ion and that the distribution of species changes via condensation (Equation 4) or hydrolysis reactions (Equation 5) so as to avoid increases in H + concentration during POM reduction or increases in OH " concentration during POM reoxidation.
  • the reactor was purged with Ar for at least 10 minutes and charged with CO to 550 kPa.
  • the reactor, equipped with a gas entrainment impeller was heated to 130°C for 6 hours.
  • the reactor, equipped with a gas entrainment impeller was charged with 2170 kPa O 2 and heated to 210°C for 4 hours.
  • a single equilibrated solution was used throughout the experiment (ten two-step cycles of reduction by CO followed by reoxidation by O 2 ). Throughout the 20-step experiment, nothing (other than CO and O 2 ) was added or removed from the system and no precipitation was observed.
  • Polyoxometates are frequently cited as compounds that are generally useful as oxidants and, more specifically, useful as intermediaries in the application of other oxidants, namely air, oxygen, hydrogen peroxide and other organic or inorganic peroxides, and ozone. Therefore, POM systems that are more easily reoxidized by these oxidants are desirable. Such systems would reduce reaction times and conditions in order to minimize operating and capital costs. It is well established that many transition metals can be used to facilitate oxidation reactions with oxygen, peroxides and ozone (Fe, Mn and Cu are commonly cited examples).
  • transition metals Under acidic conditions, many of these transition metals can be used homogeneously in aqueous systems, however, at neutral or basic pHs, many of these metals would have to be used heterogeneously. This may create handling and mass transfer problems.
  • the breadth of substitution chemistry available to POMs allows one to incorporate a wide variety of transition metal into homogenous, aqueous solutions over a broad range of pH by incorporating them into the POM structures.
  • the use of equilibrated POM systems allows one to incorporate small amounts of the transition metals as needed to increase the rate of reactions of reduced POMs with oxygen or other oxides.
  • the advantage of incorporating transition metals into the equilibrated polyoxometalate systems is demonstrated by the results shown in Example 20.
  • the equilibrated POM solutions described in the present invention are truly engineering systems. By making small changes in the ratios of component elements used in their syntheses, the nature and relative concentrations of species present in the system are smoothly varied over a continuous range of equilibrium distributions. This flexibility provides a means to design for and control the physical and chemical properties of the catalyst system as needed for specific applications. For example, diverse applications might require different buffering capacities or that solutions operate at specific pH values. The relative concentration of the target POM within the equilibrium distribution of species can be maximized for specific processes or even changed for individual process steps to enhance overall performance. The manipulation of POM solutions as equilibrium-state systems provides a unique opportunity by which catalyst performance can be finely tuned or otherwise optimized.
  • the buffering capacities of the equilibrated POM solutions can be systematically altered as required for desired applications.
  • a large buffering capacity may be needed for systems where oxidation and reduction of the target POM occurs in separate process steps.
  • a much smaller buffering capacity might be needed in a system wherein oxidation and reduction of the POM catalyst are simultaneous.
  • One way the buffering capacity of the system can be systematically altered is to vary the relative amounts of acidic versus basic oxides used as synthetic precursors for introducing the transition-metal or main-group component elements (e.g., WO 3 vs. Na 2 WO 4 for the W(IV)— note that Na 2 WO 4 is a combination of WO 3 and two equivalents of NaOH).
  • the dashed line shows the calculated pH values expected had the added H + ions not been consumed.
  • each polyoxometalate species possesses substantial thermodynamic stability only within a well-defined range of pH values. If the pH of a POM solution is set beyo: d a species' range of stability, it will eventually decompose via hydrolysis or condensation reactions until equilibrium is established. The pH of the equilibrated solution might be different from the initially set value. The new pH value may be one at which the POM species is stable or, the POM anion may no longer be present at a significant (measurable) concentration. However, the pH can be adjusted and the desired distribution POM species in an equilibrated solution ensured by systematic alteration of the ratios of elements present.
  • polyoxometalates of particular structures and composed of particular elements are thermodynamically stable.
  • Polyoxotungstates of a particular structure and composition are generally stable at higher pH values that are isostructual polyoxomolybdates.
  • ⁇ -Keggin-fSiVW ⁇ O ⁇ ] 5" possesses greater thermodynamic stability at higher pH values than does
  • the nature of the heteroatoms within specific structures has a large affect. Higher charge and charge density of the POM anion, both altered by choice of heteroatom element or valence state, tends to correlate with greater stability at higher pH values. Stability is also influenced by the size and electronegativity of the heteroatom ion.
  • ⁇ -Keggin-[PW 12 O 40 ] 3" is stable at pH values between 1 and 2
  • ⁇ -Keggin-[SiW 12 O 40 ] 4" is stable to pH 4
  • ⁇ -Keggin-[AIW 12 O 40 ] 5" possesses substantial kinetic (and perhaps thermodynamic) stability to pH 6.
  • specific polyoxometalate structures are themselves stable over different pH ranges. For example, tungstate is only present at relatively high pH values, paratungstates are stable at near-neutral pH values, metatungstate at lower pH values (ca. 3-6), and decatungstate at still lower pH values (ca. 0-3).
  • the equilibrated solutions can be altered so as to increase or decrease the concentrations of specific POM species. If a particular species is responsible for a desired reaction, increasing its concentration may increase the rate at which the reaction occurs. There are several benefits of a faster reaction: one can decrease the reactor size to lower capital costs, decrease reaction temperatures to lower operating costs or decrease reaction times to increase throughput. Additionally, product quality can be improved if higher reaction temperatures or longer exposure times have degrading effects.
  • concentration of individual species in equilibrated solutions can be changed through systematic alteration of the ratios of elements present.
  • an equilibrated solution such as Na 6(+1 5) [AI 1(+05) VW 11(+1) O 40 ], which contains a large concentration of the target anion, [AIVW ⁇ O ⁇ ] 6" , relative to the other Al(lll)- and V(V)-containing species might be chosen.
  • Table 1 shows the distributions of species present in two POM solutions that possess different relative ratios of sodium (Na + ). To simplify discussion, only a directly pertinent subset of the total diversity of species present is listed. A qualitative comparison of the reduction potentials, Eo, of two specific anions is provided below the table.
  • Table 1 Simplified distributions of species in solutions containing different relative rati
  • Solution A the species possessing the higher reduction potential, [SiVW ⁇ O ⁇ ] 5" , is present at a higher relative concentration (2:1 ) than is the weaker oxidant, [SiV 2 W 10 O 40 ] 6' .
  • Solution A should thus be more highly oxidizing. This expectation is confirmed experimentally by comparing the rates of wood pulp delignification (i.e., rates of lignin oxidation) obtained using the two solutions.
  • the results in Table 8 of Example 17 show that for the same reaction conditions, effectiveness decreases in the order: Na 5(+1) [SiVW 11 O 40 ] > Na ⁇ fSiVW ⁇ O > Na ⁇ SiVWnO , as indicated by the final kappa number of the wood pulp.
  • Solution B should be more readily oxidized by oxygen (O 2 ) under the same reaction conditions because the reduced form of the species with the less positive reduction potential (i.e., [SiV 2 W 10 O 40 ] 7" , the 1e " -reduced form of [SiV 2 W 10 O 40 ] 7" ) is present at a higher relative concentration.
  • O 2 oxygen
  • Na 5(+4) SiVMo 2 W 9 O 40 solution is reoxidized at a greater rate than is the reduced Na 5(+2) SiVMo 2 W 9 O 40 solution.
  • the present invention is a method of delignifying wood pulp, wood fiber, linocellulosic pulp, lignocellulosic fiber, comprising the step of degrading dissolved lignin and polysaccharide fragments to volatile organic compounds and water.
  • the temperature of the degradation reaction is between 100°C and 400°C
  • the degradation time reaction is between 0.5 and 10 hours
  • the pressure of the oxidant is between 15 to 1000 psia
  • the degradation reaction takes place in a vessel capable of withstanding pressures exceeding the vapor pressure of the solution plus any additional applied gaseous pressure.
  • an equilibrated solution may be referred to as Na 6(+2) [SiV 2 W 10 O 40 ]: the target POM anion of this solution is the sodium salt of the Keggin anion [SiV 2 W 10 O 40 ] 6' (i.e., Na 6 [SiV 2 W 10 O 40 ]), that exists as one component of the complex equilibrium mixture.
  • the solution contains two Na + ions (and two equivalents of HO " ) in excess of the six dictated by the empirical formula of the target POM. This excess is indicated by the subscripted "+2" in parentheses.
  • an equilibrated solution may be referred to as Na 6(+1 5) [AI 1(+05) VW 11(+1) O 40 ]: the target POM anion of this solution is the sodium salt of the Keggin anion [AIVW ⁇ O ⁇ ] 6' (i.e., Na AIVW ⁇ O ⁇ ]).
  • the solution contains 1.5 additional equivalents of Na + ions as indicated by the subscripted "(+1.5)", one-half an additional equivalent of Al(lll) ions as indicated by the subscripted "(+0.5)” and one additional equivalent of W(VI) ions as indicated by the subscripted "(+1 )”.
  • an equilibrated solution may be referred to as Na 5(+1.5) [SiV 1 in this case the target POM salt is defined as Beyond the ratio of elements dictated by the empirical formula of this POM anion, the solution contains 1.5 additional equivalents of ⁇ a + ions as indicated by the subscripted "(+1.5)", one-tenth of an equivalent less of V(V) than the number of equivalents dictated by the empirical formula (i.e., 0.1 equivalents less that the implied subscript of "1" for V(V) in the formula) as indicated by the subscripted "(-0.1 )".
  • solution concentrations will be presented as if the solution contained only the target POM, although it is well understood that other species are present in the equilibrated solution.
  • Use of the herein described notation facilitates clear definition of the total concentrations of individual elements present in each equilibrated solution.
  • an equilibrated 0.5 M solution of Na 6(+1 5) [AI 1(+05) VW 11(+1) O 40 ] contains (in total): 3.75 M Na + , 0.75 M Al(lll), 0.5 M V(V) and 6 M W(VI).
  • the subscripted numbers associated with oxygen (O) atoms in the formulas used to describe the present inventions are limited to those defined by the empirical formulas of the target POMs — no subscripted parenthetical numbers are provided.
  • relative ratios of O 2" and HO " added directly to water in the preparation of these solutions are explicitly and fully defined by reference to the nature and relative molar ratios of the transition-metal and main-group oxides and hydroxides used as synthetic starting materials.
  • the delignification of wood-pulp is used to demonstrate the utility of the present invention.
  • the kappa number obtained by permanganate oxidation of residual lignin, is an index of how much lignin is present within a wood or pulp sample. Although difficult to measure accurately or to interpret when only small amounts of lignin are present, kappa numbers are a widely used and easily recognized index of lignin content. For relatively small pulp samples, microkappa numbers are determined. Microkappa numbers were obtained using TAPPI methods T236 om-85 and um-246. Microkappa number determinations are used in several examples below to demonstrate that lignin-like material is effectively degraded or otherwise removed from pulp during reaction with equilibrated POM solutions.
  • the viscosity of a pulp sample is proportional to the average chain length of cellulose polymers within the pulp fibers. Consequently, retention of pulp viscosity is one of several criteria indicating that cellulose fibers have not been degraded during delignification. Viscosity values are commonly used in conjunction with kappa numbers to determine the selectivity of a delignification agent. TAPPI test method T230 om-89 is used to measure the viscosity of aqueous cupriethylene diamine solutions in which standard amounts of pulp samples have been dissolved. Example 1.
  • Example 1a K S ⁇ -UHoO.
  • Example 1 b K SiV,W ⁇ n Q., xHoO.
  • Fig. 3 show the 51 V NMR spectrum of the pure, of K 6 [SiV 2 W 10 O 40 ] (mixture of positional isomers) in D 2 O.
  • Example 1d K 7 rSiV l V v W,XU «13H.,O. V lv OSO 4 « 3H 2 O (3.91 g, 18.0 mmol) was dissolved in water (3 L) to give a blue solution (pH 3.2). Solid K 9 [SiV v W 10 O 39 ] « 14H 2 O (50.4 g, 16.0 mmol) was slowly added to the solution in portions to give a brown solution (pH 5.5). The reaction was stirred for at least 1 additional hour. After this time, the solution was filtered to remove a small amount of precipitate. Solid KCl (400 g, 5.4 mol) was added to the filtrate to give a fine brown precipitate.
  • Example 1e K c SiVMoW, n Q,n » xH,0.
  • Pulp delignification using kinetically-derived without a buffer Pulp delignification using kinetically-derived without a buffer.
  • K 5 [SiVW 11 0 4Q l-12H 2 ⁇ (23.7 g, 7.5 mmol) was dissolved in water (139 mL).
  • Kraft softwood pulp (4.6 g o.d. pulp containing 11 g water) was mixed with the POM solution.
  • the pH of the mixture was 5.7 and was adjusted to 6.0 using a small amount of KHCO 3 .
  • the mixture was placed in a 1 L glass lined Parr reactor equipped with a 316 stainless-steel stirrer. The reactor was purged thoroughly with nitrogen. It was then heated to 125°C, taking one hour, and maintained at temperature for two hours. The reaction was then quenched by cooling the reactor in a water bath and the pulp filtered and washed.
  • the POM solution had been reduced by 84% and had a final pH of 2.1.
  • the equilibrated solutions have been prepared under a variety of experimental conditions by mixing hydroxides or neutral or anionic oxides of transition-metal or main-group elements and water and heating the mixtures to temperatures sufficiently high such that they react to give solutions containing target heteropolyoxotungstates of the general formula present in thermodynamic equilibrium with additional compounds also derived from the starting materials.
  • Example 3a Equilibrated aqueous solution of 0.1 M Na 6(J . 2) [SiV 2 W 1 O 40 ].
  • NaVO 3 0.76 g, 6.2 mmol
  • WO 3 » H 2 O 6.00 g, 24.0 mmol
  • Fig. 5 shows by 51 V NMR the presence of [SiV 2 W 10 O 40 ] 6" isomers in solution (compare to Fig. 3, the 51V NMR spectrum of pure [SiV 2 W 10 O 40 ] 6" ) in equilibrium with smaller amounts of additional isopoly- and heteropolyoxotungstates, such as [V 2 W 4 0 19 ] 4" .
  • Example 3c Eguilibrated agueous solution of 0.2 M Na 9( 2) [SiV 2 W 10 Q ⁇ 0 ].
  • Fig. 10 demonstrates by 51 V NMR that the concentration of target POM anions in the equilibrated solutions described herein can remain fairly constant over a range of pH values. However, small changes in the solution pH do reflect changes in equilibrium distributions that are likely vital to the buffer capacity described in Example 6.
  • Buffering capacity titration of equilibrated Na 6(+x) [SiV 2 W 10 O 40 ] solutions at 70°C.
  • This example demonstrates that equilibrated solutions containing a target heteropolyoxotungstate of the general formula prepared in the manner described above can be used to oxidize a substrate (for example, lignin in wood pulp). The solutions can then be reoxidized under conditions that also mineralize the soluble organic by-products of lignin oxidation. This example also demonstrates that the solution can be used repeatedly and that during all the lignin oxidation and POM regeneration cycles, the pH is maintained at a constant level.
  • a substrate for example, lignin in wood pulp
  • Fig. 13 demonstrates the ability of the equilibrated 0.1 M Na 6(+2) [SiV 2 W 10 O 40 ] catalyst solution to maintain a stable pH throughout multiple delignification and wet-oxidation steps.
  • This example demonstrates that equilibrated solutions containing a target heteropolyoxotungstate of the general formula prepared in the manner described above can be used to oxidize a substrate (for example, lignin in wood pulp). The solutions can then be reoxidized under conditions that also mineralize the soluble organic by-products of lignin oxidation. This example also demonstrates that the solution can be used repeatedly and that during all the lignin oxidation and POM regeneration cycles, the pH is maintained at a constant level. This experiment was carried out at a larger scale using a more concentrated POM solution than Example 7 and was extended to a larger number of oxidation/reduction cycles.
  • Example 9a Agueous solution of Na R fAI(AI)W., ., Ojg] . .
  • Sodium tungstate dihydrate (Na 2 WO 4 '2H 2 O, 100 g, 0.304 mol) was dissolved in 400 mL of H 2 O in a 1000 mL 3-neck round bottomed-flask containing a magnetic stirring bar and fitted with an addition funnel and condenser.
  • Hydrochloric acid (ca. 23.0 mL, 0.276 mol) was added to the solution dropwise with vigorous stirring to pH 7.7 (use of a calibrated pH meter in the solution during this procedure was necessary). After every several drops the addition was momentarily stopped to allow the local precipitate of tungstic acid to dissolve.
  • the 183 W NMR spectrum displayed 23 signals ranging from -43 to -200 ppm, assigned to two isomers of C s symmetry (tentatively ⁇ , and ⁇ 3 , 6 signals expected from each) and one of C ⁇ symmetry (tentatively ⁇ 2 , 11 signals expected).
  • Example 9b Dodecatungstoaluminic Acid, H ? [AIW 1? O, n 1.
  • the solution which contained Na 6 [AI(AIOH 2 )W 11 O 39 ], was transferred to a 1000 mL round-bottomed flask fitted with a reflux condenser.
  • the solution was acidified to pH 0 by careful dropwise addition of concentrated sulfuric acid (ca. 20 mL, 0.376 mol). After the pH reached 0, an additional 3 mL of cone, sulfuric acid was added and the solution was heated to reflux. The solution became cloudy and slightly yellow as the acid was added, but usually cleared within 16 hours of the beginning of reflux. To ensure complete conversion to product, the solution was kept at reflux for 6 days. Then, after cooling to room temperature, the solution was filtered (if cloudy) using a medium glass frit (this was typically not necessary if the two steps were performed in quick succession, i. e., provided that the
  • the mixture was shaken more vigorously, still with frequent venting, and allowed to settle until three layers separated.
  • the top clear colorless layer was diethyl ether
  • the middle somewhat cloudy layer was the aqueous phase
  • the bottom layer (a dense, pale yellow, viscous liquid) was the etherate of H 5 [AIW 12 O 40 ].
  • the bottom (etherate) layer was collected and the shaking and venting procedure was repeated until the etherate layer no longer formed (the aqueous layer appeared clearer as the extraction neared completion).
  • the combined etherate layers (about 20 mL) were concentrated to dryness by rotary evaporation.
  • the crude product (69.2 g, 95%) was reprecipitated by dissolving in 20 mL of hot water, concentrating to a volume of 23 mL by gentle heating, and then cooling to 0°C for 16 hours. Yield: 50.46 g, 64%.
  • Dodecatungstoaluminic acid is a water-soluble slightly yellow amorphous solid.
  • metal implements were not used in handling it as a solid or in solution.
  • the polyanion was stable in water below pH 6 and characterized by NMR and IR spectroscopy.
  • Example 9c Potassium Undecatungstoaluminate, K Q rAIW 1 ⁇ O, Q 1*12H,0.
  • Dodecatungstoaluminic acid H 5 [AIW 12 O 40 ]'13H 2 O, 43.76 g, 14.1 mmol
  • H 2 0 Dodecatungstoaluminic acid
  • Three equivalents of potassium carbonate K 2 CO 3 « 1.5H 2 O, 6.97 g, 42.3 mmol
  • the pH should rise to about 2.
  • Another 5 equivalents of potassium carbonate K 2 CO 3 » 1.5H 2 O, 11.62 g, 70.5 mmol, dissolved in 20 mL of H 2 O) were added dropwise carefully over about 60 minutes.
  • the pH of the solution should not be allowed to rise above 8 until at least 80% of the potassium carbonate solution has been added and should at all times be kept below 8.5. A white precipitate began to form as addition of the potassium carbonate solution proceeded. The final pH of the mixture should be near 8.25. After addition of the potassium carbonate solution was complete, the mixture was cooled to 0°C for several hours. The product, a fine white precipitate, was then collected, washed three times with H 2 O and dried on a medium glass frit. Yield: 41.8 g, 92%.
  • the potassium salt of the lacunary anion is a white amorphous solid, which is slightly soluble in water (2 g/100 mL at 22°C).
  • Example 9f KJAlMn(H,O)W Q,J.
  • the manganese (II) complex of is a yellow amorphous powder and was characterized in the solid state by IR (KBr pellet, cm “1 ): 934, 872, 797, 766, 697, 528 and 487.
  • POM solutions containing target polyoxotungstates of the general formula have been prepared under a variety of experimental conditions by mixing hydroxides or neutral or anionic oxides of transition-metal or main-group elements and water and heating the mixtures to temperatures sufficiently high such that they react to give solutions containing target heteropolyoxotungstates of the general formula present in thermodynamic equilibrium with additional compounds also derived from the starting materials.
  • Example 10a Equilibrated aqueous solution containing the sodium salt of the
  • WO 3 'H 2 O (2.124 g) were placed in a 10 mL volumetric flask. The flask was filled with water to a total volume of 10 mL, and the solution was placed in a Teflon liner inside a stainless steel pressure vessel. The pressure vessel was heated in a 200°C oven for 2 days (without stirring); during this time most of the solid dissolved. The solution was brown due to a small amount of reduction. The presence of the target POM anion, [ANYJ O 40 f ⁇ was verified by 51 V and 27 AI NMR; before collecting the 51 V and 27 AI NMR spectra, it was fully oxidized to a clear-yellow solution by brief exposure to bromine vapors.
  • Example 10b Eguilibrated aqueous solution containing the sodium salt of the
  • Fig. 14 demonstrates by 5 V NMR the presence of in equilibrium with smaller amounts of additional isopoly- and heteropolyoxotungstates, such as [V 2 W 4 O 19 ] 4" , [V 3 W 3 O 19 ] 5" and [HV 3 W 3 O 19 ] 4" .
  • Example 10c Eguilibrated agueous solution of 0.25 M Na 6( . 2)
  • Figs. 15 and 16 demonstrate by 51 V NMR and 27 AI NMR that these solutions can be prepared using a variety of experimental conditions.
  • Fig. 14 shows the 51 V NMR spectrum of [AIVW ⁇ O ⁇ ] 6" synthesized from the elemental oxides described in Example 10b and Fig. 15 is the spectrum of the solution prepared using an excess of NaOH as described in Example 10c.
  • the narrow signal at -511 ppm (labeled (2)) in the 51 V NMR spectrum in Fig. 15 corresponds to [V 2 W 4 O 19 ] 4" ; its area corresponds to 18% of the total amount vanadium in solution.
  • the major product (82% of the total amount of vanadium) of the synthesis is the target anion, ⁇ - [AIVW ⁇ O ⁇ ] 6" at -536 ppm (labeled (1 )).
  • AI(OH) 3 (89.82 g, 97.7%, 1.125 mol), NaVO 3 (94.57 g, 96.7%, 0.75 mol), WO 3 (2089.18 g, 99.88%, 9 mol) and NaOH (196.97 g, 99%, 4.875 mol) were mixed with water (1341 mL) in a stirred, 2 L 316 stainless steel Parr Reactor. The reactor was charged with 1480 kPa 0 2 and heated to 210°C for 13 hours. The solution was filtered to remove a small amount of solids.
  • the final solution was 1.714 L in volume, 2.179 g/mL in density and 0.438 M in concentration (based on vanadium concentration), had a pH of 8.1 and 2.3% of the vanadium present had been reduced to V(IV). 1.23 L of solution was concentrated to 1 L. This solution was mixed with 33.29 g softwood Kraft pulp (dry equivalent), kappa 31.8 and viscosity 31.4 mPa » s, which contained 0.08 L of water giving a pulp slurry of 3% consistency and a 0.5 M solution. The delignification was carried out in a 2 L stainless steel Parr reactor, equipped with a tapered helical stirrer, that was purged with N 2 for 5 minutes before heating.
  • the reactor was heated to 150°C and held at this temperature for 3 hours. The reaction was then quenched and the pulp filtered and washed with water. The resulting pulp had a final kappa number of 4.8 and viscosity of 16.3 mPa*s. After the reaction, 41.2% of the vanadium present was reduced to V(IV) and the pH of the solution was 8.1.
  • This example demonstrates that equilibrated solutions containing a target heteropolyoxotungstate of the general formula prepared in the manner described above can be used to oxidize a substrate (for example, lignin in wood pulp). The solutions can then be reoxidized under conditions that also mineralize the soluble organic by-products of lignin oxidation. This example also demonstrates that the solution can be used repeatedly and that during all the lignin oxidation and POM regeneration cycles, the pH is maintained at a constant level.
  • a substrate for example, lignin in wood pulp
  • AI(OH) 3 (11.04 g, 97.7%, 135 mmol), NaVO 3 (11.70 g, 96.7%, 90 mmol), WO 3 (251.82 g, 99.88%, 1080 mmol) and NaOH (46.38 g, 50% solution, 585) were mixed with water (150 mL) in a stirred, 300 mL Hastelloy C Parr Micro Reactor. The reactor was charged with 1480 kPa O 2 and heated to 200 °C for 12 hours. The resultant solution had a pH of 7.4 and 2.8% of the vanadium present had been reduced to V(IV). This mixture was used in the subsequent reaction with wood pulp without further purification.
  • AI(OH) 3 (11.04 g, 97.7%, 135 mmol), NaVO 3 (11.70 g, 96.7%, 90 mmol), WO 3 (251.82 g, 99.88%, 1080 mmol) and NaOH (46.38 g, 50% solution, 585) were mixed with water (150 mL) in a stirred, 300 mL Hastelloy C Parr Micro Reactor. The reactor was charged with 1480 kPa 0 2 and heated to 200 °C for 12 hours. The final solution had a pH of 7.2 and 1.0% of the vanadium present had been reduced to V(V). This solution was used in the subsequent oxidation of CO without any purification.
  • Example 15 Equilibrated aqueous solution of 0.5M Na 5(+1) [PV 2 W 10 O 40 ].
  • the following is an example of the single-step synthesis of an equilibrated POM solution containing target polyoxotungstates of the general formula.
  • the equilibrated solution was prepared by mixing hydroxides or neutral or anionic oxides of transition-metal or main-group elements and water and heating the mixtures to temperatures sufficiently high such that they reacted to give solutions containing target heteropolyoxotungstates of the general formula in thermodynamic equilibrium with additional compounds also derived from the starting materials.
  • This example further demonstrates the generality of the present invention. Na 2 HPO 4 (14.21 g, 100 mmol), NaVO 3 (25.26 g, 200 mmol), WO 3
  • Example 16 Wood-pulp delignification using an equilibrated aqueous solution containing 0.5 M Na 5(+1) [PV 2 W 10 O 40 ].
  • Na 2 HPO 4 (42.6 g, 300 mmol), NaVO 3 (75.8 g, 600 mmol), WO 3 (232.15 g, 1000 mmol) and NaOH (24.5 g, 600 mmol) were mixed with water (400 g) in a stirred 1 L 316 SS Parr Reactor equipped with a glass liner.
  • the reactor was pressurized with O 2 (700 kPa) and heated to 210°C over the course of 1/2 hour and held at this temperature for 14 hours.
  • the pH of the final solution was 4.7.
  • This solution mixed with 18.6 g softwood Kraft pulp (dry basis), kappa 31.8 and viscosity 31.4 mPa « s, which contained 0.04 L of water resulting in a pulp slurry of 3% consistency and a 0.5 M solution.
  • the delignification was carried out in a 1 L stainless steel Parr reactor equipped . with a tapered helical stirrer that was purged with N 2 for 5 minutes before heating. The reactor was heated to 135°C and held at this temperature for 1 hour. The reaction was then quenched by cooling the reactor and the pulp filtered and washed with water. The resulting pulp had a final kappa number of 15.4 and viscosity of 23.0 mPa « s. After the reaction, 29% of the vanadium present was reduced to V(IV) and the pH of the solution was 5.0.
  • the reduced solution liquor containing 0.5 M Na 5(+2) [SiVMo 2 W 9 O 40 ] from Example 17 was split into 150 mL aliquots. To one aliquot, NaOH (6.19 g, 150 mmol) was added now making it essentially 0.5 M Na 5(+4) [SiVMo 2 W 9 O 40 ]. None was done to the other bleach liquor aliquot.
  • the solutions were each, in turn, placed into a 300 mL 316 stainless steel Parr mini reactor equipped with a gas entrainment impeller. The reactor was purged with N 2 and heated to 210°C at which time 1400 kPa 0 2 was injected into the system.
  • the following is an example of the single-step synthesis of an equilibrated POM solution containing target polyoxotungstates of the general formula.
  • the equilibrated solution was prepared by mixing hydroxides or neutral or anionic oxides of transition-metal or main-group elements and water and heating the mixtures to temperatures sufficiently high such that they reacted to give solutions containing target heteropolyoxotungstates of the general formula in thermodynamic equilibrium with additional compounds also derived from the starting materials.
  • This example further demonstrates the generality of the present invention.
  • Example 22 The solution synthesized in Example 22 was then mixed with softwood Kraft pulp (Kappa 30, viscosity 30.5 mPa-s) to a consistency of 3% and heated in the Parr reactor to 140°C under N 2 for 2 hours. Using the softwood Kraft pulp (Kappa 30, viscosity 30.5 mPa-s) to a consistency of 3% and heated in the Parr reactor to 140°C under N 2 for 2 hours. Using the following softwood Kraft pulp (Kappa 30, viscosity 30.5 mPa-s) to a consistency of 3% and heated in the Parr reactor to 140°C under N 2 for 2 hours. Using the following softwood Kraft pulp (Kappa 30, viscosity 30.5 mPa-s) to a consistency of 3% and heated in the Parr reactor to 140°C under N 2 for 2 hours. Using the following softwood Kraft pulp (Kappa 30, viscosity 30.5 mPa-s) to a consistency of 3% and heated in the Parr reactor to
  • Example 24 Equilibrated aqueous solution of 0.1
  • the following is an example of the single-step synthesis of an equilibrated POM solution containing target polyoxotungstates of the general formula.
  • the equilibrated solution was prepared by mixing hydroxides or neutral or anionic oxides of transition-metal or main-group elements and water and heating the mixtures to temperatures sufficiently high such that they reacted to give solutions containing target heteropolyoxotungstates of the general formula in thermodynamic equilibrium with additional compounds also derived from the starting materials.
  • This example further demonstrates the generality of the present invention.
  • the correct ratio of starting compounds Na 2 WO 4 , NaOH, Mn0 2 , W0 3 ,

Landscapes

  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Organic Chemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Wood Science & Technology (AREA)
  • Catalysts (AREA)
  • Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)

Abstract

L'invention concerne une solution homogène, aqueuse. Cette solution comprend au moins un complexe isopoly- ou hétéropolyoxometalate (POM) à base de tungstène utiles sur le plan catalytique ou sur un autre plan, présent en équilibre thermique avec toutes les espèces chimiques liées au(x) complexe(s) utile(s) par réactions entre les composés chimiques du système. Ladite solution comprend au moins un polyoxometalate de formule générale [VkNbmTanMooWp(TM)q(MG)rOs]z-, où TM représente un ion métallique de transition contenant d-électrons et MG représente un ion du groupe principal, k est compris entre 0 et 18, m entre 0 et 10, n entre 0 et 10, o entre 0 et 19, p entre 1 et 150, q entre 0 et 9, et r entre 0 et 9, k<p, m<p, n<p et o<p sous réserve que p≥1 et k+m+n+o+p≥4; et s est suffisamment grand pour que z⊃0, et où le POM utile de formule générale est présent à une concentration suffisante pour accomplir son objectif et toutes les espèces présentes à l'intérieur de la solution aqueuse équilibrée restent dissoutes.
PCT/US2000/014511 1999-05-26 2000-05-25 Systemes equilibres de catalyseur au polyoxometalate a base de tungstene Ceased WO2000071247A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU52929/00A AU5292900A (en) 1999-05-26 2000-05-25 Equilibrated tungsten-based polyoxometalate-catalyst systems

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US13607399P 1999-05-26 1999-05-26
US60/136,073 1999-05-26

Publications (1)

Publication Number Publication Date
WO2000071247A1 true WO2000071247A1 (fr) 2000-11-30

Family

ID=22471160

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/US2000/014511 Ceased WO2000071247A1 (fr) 1999-05-26 2000-05-25 Systemes equilibres de catalyseur au polyoxometalate a base de tungstene

Country Status (2)

Country Link
AU (1) AU5292900A (fr)
WO (1) WO2000071247A1 (fr)

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2006012637A3 (fr) * 2004-07-29 2007-05-03 Wisconsin Alumni Res Found Procede catalytique d'elimination de co et d'utilisation de son contenu energetique dans des flux contenant du monoxyde de carbone
WO2008106811A1 (fr) * 2007-03-02 2008-09-12 ETH Zürich Procédé d'extraction de lignine
CN109081857A (zh) * 2018-08-16 2018-12-25 河南大学 具有能量转移的芳香羧酸修饰的过渡稀土异金属嵌入的锑钨氧酸盐材料、制备方法及应用
CN110817971A (zh) * 2019-08-29 2020-02-21 吉林化工学院 一种多金属氧酸盐及其制备方法和应用
CN112225381A (zh) * 2020-07-09 2021-01-15 桂林理工大学 一种含铬废水的处理方法
CN113372395A (zh) * 2021-07-05 2021-09-10 福州大学 主族-稀土异金属簇嵌入的锑钨酸化合物及其制备方法
CN116282177A (zh) * 2023-03-22 2023-06-23 合肥学院 一种具有三维结构的多金属钨酸盐晶体材料及其制备方法
CN117563618A (zh) * 2023-11-07 2024-02-20 东北电力大学 一种磁性纳米复合光催化剂及其制备方法和应用

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN108250451B (zh) * 2018-01-29 2020-12-25 河南大学 二元有机羧酸参与的铁-镝异金属锑钨酸盐框架材料及其制备方法与应用
CN114904526B (zh) * 2022-06-13 2023-11-14 湖北拓扑来微科技有限公司 自缓冲系统Co-MOOH@MxOy整体材料的制备方法及应用

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5302248A (en) * 1992-08-28 1994-04-12 The United States Of America As Represented By The Secretary Of Agriculture Delignification of wood pulp by vanadium-substituted polyoxometalates
US5549789A (en) * 1992-08-28 1996-08-27 The United States Of America As Represented By The Secretary Of Agriculture Oxidation of lignin and polysaccharides mediated by polyoxometalate treatment of wood pulp
US6074437A (en) * 1998-12-23 2000-06-13 Unilever Home & Personal Care Usa, Division Of Conopco, Inc. Bleaching with polyoxometalates and air or molecular oxygen

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5302248A (en) * 1992-08-28 1994-04-12 The United States Of America As Represented By The Secretary Of Agriculture Delignification of wood pulp by vanadium-substituted polyoxometalates
US5549789A (en) * 1992-08-28 1996-08-27 The United States Of America As Represented By The Secretary Of Agriculture Oxidation of lignin and polysaccharides mediated by polyoxometalate treatment of wood pulp
US5552019A (en) * 1992-08-28 1996-09-03 The United States Of America As Represented By The Secretary Of Agriculture Oxidative delignification of wood or wood pulp by transition metal-substituted polyoxometalates
US5695606A (en) * 1992-08-28 1997-12-09 The United States Of America As Represented By The Secretary Of Agriculture Oxidative delignification of wood or wood pulp by transition metal-substituted polyoxometalates
US5695605A (en) * 1992-08-28 1997-12-09 The United States Of America As Represented By The Secretary Of Agriculture Oxidative delignification of wood or wood pulp by transition metal-substituted polyoxometalates
US5824189A (en) * 1992-08-28 1998-10-20 The United States Of America As Represented By The Secretary Of Agriculture Oxidative delignification of wood pulp or fibers using transition metal-substituted polyoxometalates
US6074437A (en) * 1998-12-23 2000-06-13 Unilever Home & Personal Care Usa, Division Of Conopco, Inc. Bleaching with polyoxometalates and air or molecular oxygen

Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2006012637A3 (fr) * 2004-07-29 2007-05-03 Wisconsin Alumni Res Found Procede catalytique d'elimination de co et d'utilisation de son contenu energetique dans des flux contenant du monoxyde de carbone
WO2008106811A1 (fr) * 2007-03-02 2008-09-12 ETH Zürich Procédé d'extraction de lignine
US7906687B2 (en) 2007-03-02 2011-03-15 Eth Zurich Method for the breakdown of lignin
CN109081857A (zh) * 2018-08-16 2018-12-25 河南大学 具有能量转移的芳香羧酸修饰的过渡稀土异金属嵌入的锑钨氧酸盐材料、制备方法及应用
CN109081857B (zh) * 2018-08-16 2020-09-01 河南大学 具有能量转移的芳香羧酸修饰的过渡稀土异金属嵌入的锑钨氧酸盐材料、制备方法及应用
CN110817971A (zh) * 2019-08-29 2020-02-21 吉林化工学院 一种多金属氧酸盐及其制备方法和应用
CN112225381A (zh) * 2020-07-09 2021-01-15 桂林理工大学 一种含铬废水的处理方法
CN112225381B (zh) * 2020-07-09 2022-04-26 桂林理工大学 一种含铬废水的处理方法
CN113372395A (zh) * 2021-07-05 2021-09-10 福州大学 主族-稀土异金属簇嵌入的锑钨酸化合物及其制备方法
CN116282177A (zh) * 2023-03-22 2023-06-23 合肥学院 一种具有三维结构的多金属钨酸盐晶体材料及其制备方法
CN117563618A (zh) * 2023-11-07 2024-02-20 东北电力大学 一种磁性纳米复合光催化剂及其制备方法和应用

Also Published As

Publication number Publication date
AU5292900A (en) 2000-12-12

Similar Documents

Publication Publication Date Title
US5549789A (en) Oxidation of lignin and polysaccharides mediated by polyoxometalate treatment of wood pulp
US5695606A (en) Oxidative delignification of wood or wood pulp by transition metal-substituted polyoxometalates
US6022986A (en) Manganiferous polyoxometallates, synthesis and use thereof
Izarova et al. Noble metals in polyoxometalates
Weinstock et al. A new environmentally benign technology for transforming wood pulp into paper. Engineering polyoxometalates as catalysts for multiple processes
US9302255B2 (en) Oxidation catalyst, the process for the preparation thereof and green process for selective aerobic oxidation
WO2000071247A1 (fr) Systemes equilibres de catalyseur au polyoxometalate a base de tungstene
US7645907B2 (en) Transition metal substituted polyoxometalates and process for their preparation
Corma et al. Catalytic air oxidation of thiols mediated at a Mo (VI) O2 complex center intercalated in a Zn (II)-Al (III) layered double hydroxide host
Tsang et al. Synthesis of Manganese Oxides by Reduction of KMnO4with KBH4in Aqueous Solutions
WO2007139616A1 (fr) Nouveaux polyoxométalates à substitution de ru et procédé pour leur préparation
EP2125198A1 (fr) Nouveaux polyoxométalates substitués par un métal de transition et leur procédé de préparation
Han et al. Influence of Pb element on the catalytic properties of {P 4 Mo 6}-polyoxometalate for redox reactions
Zhang et al. Oxidative desulfurization of dibenzothiophene catalyzed by molybdenum dioxide immobilized on zirconia-modified silica
Wang et al. Highly efficient CuCr-MMO catalyst for a base-free styrene epoxidation with H 2 O 2 as the oxidant: synergistic effect between Cu and Cr
Liu et al. Synthesis and chemical characterization of complexes containing semiquinone units bridged by pentaoxodimolybdate groups. Structural and electrochemical studies of [(n-C4H9) 4N] 2 [Mo4O10 (C6H2O4) 2] and [(n-C4H9) 4N] 3 [Mo6O15 (C6O6) 2] and of an analogous tetraoxydibenzofuran complex,[(n-C4H9) 4N] 2 [Mo4O10 (C12H4O5) 2], prepared from metal-mediated radical coupling of 1, 2, 4-trihydroxybenzene precursors
Maciuca et al. Mild oxidation of tetrahydrothiophene to sulfolane over V-, Mo-and W-containing layered double hydroxides
Marchena et al. Titanium substituted potassium tantalates (KTaxTi1-xO3 x= 1.0, 0.8, 0.6, 0.5): Catalysts for the methyl phenyl sulfide oxidation
Molchanov et al. Synthesis of heteropoly acids and their salts using mechanochemical activation
Reiner et al. Thermodynamically stable, self-buffering polyoxometalate delignification system
Jiang et al. Production of NMSBA from the oxidation of NMST by air under the catalysis of sandwich‐type polyoxometalate
Murugesan et al. 12-B heteropolyanions as ligands: Synthesis, spectral characterisation and solution studies of [MnIVThMo12O42] 4−,[MnIVUMo12O42] 4− and [VIVCeMo12O42] 4−
JP3203723B2 (ja) 還元ポリオキソアニオン系化合物の酸化方法
JP3203722B2 (ja) 還元ポリオキソアニオン系化合物の酸化方法
CN115974912A (zh) 一种乙酰丙酮氧钒的制备方法

Legal Events

Date Code Title Description
AK Designated states

Kind code of ref document: A1

Designated state(s): AE AG AL AM AT AU AZ BA BB BG BR BY CA CH CN CR CU CZ DE DK DM DZ EE ES FI GB GD GE GH GM HR HU ID IL IN IS JP KE KG KP KR KZ LC LK LR LS LT LU LV MD MG MK MN MW MX MZ NO NZ PL PT RO RU SD SE SG SI SK SL TJ TM TR TT TZ UA UG UZ VN YU ZA ZW

AL Designated countries for regional patents

Kind code of ref document: A1

Designated state(s): GH GM KE LS MW MZ SD SL SZ TZ UG ZW AM AZ BY KG KZ MD RU TJ TM AT BE CH CY DE DK ES FI FR GB GR IE IT LU MC NL PT SE BF BJ CF CG CI CM GA GN GW ML MR NE SN TD TG

DFPE Request for preliminary examination filed prior to expiration of 19th month from priority date (pct application filed before 20040101)
121 Ep: the epo has been informed by wipo that ep was designated in this application
REG Reference to national code

Ref country code: DE

Ref legal event code: 8642

122 Ep: pct application non-entry in european phase
NENP Non-entry into the national phase

Ref country code: JP