Selective conversion of cellobiose and cellulose into gluconic acid in water in the presence of oxygen, catalyzed by polyoxometalate-supported gold nanoparticles

Gold nanoparticles loaded onto Keggin-type insoluble polyoxometalates (Cs(x)H(3-x)PW(12)O(40)) showed superior catalytic performances for the direct conversion of cellobiose into gluconic acid in water in the presence of O(2). The selectivity of Au/Cs(x)H(3-x)PW(12)O(40) for gluconic acid was significantly higher than those of Au catalysts loaded onto typical metal oxides (e.g., SiO(2), Al(2)O(3), and TiO(2)), carbon nanotubes, and zeolites (H-ZSM-5 and HY). The acidity of polyoxometalates and the mean-size of the Au nanoparticles were the key factors in the catalytic conversion of cellobiose into gluconic acid. The stronger acidity of polyoxometalates not only favored the conversion of cellobiose but also resulted in higher selectivity of gluconic acid by facilitating desorption and inhibiting its further degradation. On the other hand, the smaller Au nanoparticles accelerated the oxidation of glucose (an intermediate) into gluconic acid, thereby leading to increases both in the conversion of cellobiose and in the selectivity of gluconic acid. The Au/Cs(x)H(3-x)PW(12)O(40) system also catalyzed the conversion of cellulose into gluconic acid with good efficiency, but it could not be used repeatedly owing to the leaching of a H(+)-rich hydrophilic moiety over long-term hydrothermal reactions. We have demonstrated that the combination of H(3)PW(12)O(40) and Au/Cs(3.0)PW(12)O(40) afforded excellent yields of gluconic acid (about 85%, 418 K, 11 h), and the deactivation of the recovered H(3)PW(12)O(40)-Au/Cs(3.0)PW(12)O(40) catalyst was not serious during repeated use.     

Catalytic synthesis of diphenolic acid from levulinic acid over cesium partly substituted Wells–Dawson type heteropolyacid

A series of insoluble cesium partly substituted Wells–Dawson type heteropolyacids, Cs_xH_6−xP₂W₁₈O₆₂ (x = 1.5–6.0), were synthesized and characterized using the techniques including UV–vis/DRS, FT-IR, XRD, XPS, and N₂ porosimetry. As the unique and reusable solid acid catalysts, Cs_xH_6−xP₂W₁₈O₆₂ salts were applied to produce diphenolic acid by the condensation reaction of phenol with bio-platform molecule, levulinic acid. For comparison, cesium partly substituted Keggin type heteropolyacids (Cs_xH_3−xPW₁₂O₄₀, x = 1.0–3.0), HCl, HZSM-5, and MCM-49 were also tested. Influences on the catalytic activity and selectivity were considered for factors including solvent, molar ratio of phenol to levulinic acid, amount of catalyst, reaction temperature, stirring speed, and reaction time. The experimental results demonstrated that both Cs_1.5H_4.5P₂W₁₈O₆₂and Cs_2.5H_0.5PW₁₂O₄₀ exhibited excellent catalytic performance under solvent-free conditions. Furthermore, both selectivity and activity of Cs_1.5H_4.5P₂W₁₈O₆₂ were higher than those of Cs_2.5H_0.5PW₁₂O₄₀. Reasons for the different catalytic behaviors between two types of cesium partly substituted heteropolyacids were investigated.     

Cs取代对Ni-H3PW12O40/SiO2催化剂结构性质和催化性能的影响

采用两步浸渍法和载体上的原位反应制备了一系列Cs部分取代的Ni-Cs_xH_3-xPW₁₂O₄₀/SiO₂催化剂,并用N₂吸附比表面积测定(BET)、电感耦合等离子体发射光谱(ICP)、X射线衍射(XRD)、拉曼光谱(Raman)、原位X射线衍射(in situ XRD)、NH₃程序升温脱附(NH₃-TPD)、H₂程序升温还原(H₂-TPR)、H₂程序升温脱附(H₂-TPD)、吡啶吸附傅里叶变换红外(FTIR)光谱等分析测试技术对催化剂进行了表征. 以正癸烷为模型化合物,对催化剂的加氢裂化性能进行了评价. 结果表明,8%Ni-50%Cs_1.5H_1.5PW/SiO₂催化剂具有最高的C₅₊收率,明显优于8%Ni-50%H₃PW/SiO₂催化剂和工业催化剂. 随着Cs 在Cs_xH_3-xPW中比例的增加,正癸烷的转化率逐渐降低,而C₅₊选择性则逐渐提高. 当催化剂具有合适的孔径时,选择性的提高是由于催化剂酸性的减弱,而转化率的降低则是由于催化剂加氢能力的减弱.     

Catalytic Decomposition of Lignin Model Compounds to Aromatics over Acidic Catalysts

Recent progress on the catalytic decomposition of lignin model compounds to aromatics was reported in this review. Cesium-exchanged heteropolyacid catalysts (Cs_xH_3.0?xPW₁₂O₄₀), palladium catalysts supported on cesium-exchanged heteropolyacid (Pd/Cs_xH_3.0?xPW₁₂O₄₀), and palladium catalysts supported on various activated carbon aerogels (ACAs) (Pd/ACA-SO₃H (X), Pd/XCs_2.5H_0.5PW₁₂O₄₀/ACA, Pd/Cs_xH_3.0?xPW₁₂O₄₀/ACA, and Pd/Cs_2.5H_0.5PW₁₂O₄₀/ACA-SO₃H) were prepared, and they were employed for the decomposition of C–O bond in lignin to aromatics. Phenethyl phenyl ether, benzyl phenyl ether, and 4-phenoxyphenol were used as dimeric lignin model compounds representing for β-O-4, α-O-4, and 4-O-5 bonds in lignin, respectively. It was observed that Cs_xH_3.0?xPW₁₂O₄₀ and Pd/Cs_xH_3.0?xPW₁₂O₄₀ were highly active for the decomposition of phenethyl phenyl ether and benzyl phenyl ether to aromatics. However, these catalysts showed very low catalytic performance in the decomposition of 4-phenoxyphenol. Palladium catalysts supported on various ACAs (Pd/ACA-SO₃H (X), Pd/XCs_2.5H_0.5PW₁₂O₄₀/ACA, Pd/Cs_xH_3.0?xPW₁₂O₄₀/ACA, and Pd/XCs_2.5H_0.5PW₁₂O₄₀/ACA-SO₃H) were efficient for the decomposition of 4-phenoxyphenol to aromatics. Acidity of the catalysts played a key role in determining the catalytic performance in the decomposition of 4-phenoxyphenol to aromatics.     

Catalytic effects of some Keggin-type heteropoly acids and polyoxometalates on selective nitration of phenols

Catalytic amounts of heteropoly acids and polyoxometalates promoted mononitration of phenolic compounds using iron(III) nitrate nonahydrate and bismuth(III) nitrate pentahydrate in dichloromethane at room temperature. Tungstophosphoric acid cesium salt, Cs_2.5H_0.5PW₁₂O₄₀, in a heterogeneous phase, exhibited significant rate enhancement of reactions as well as ortho selectivity without over-nitration and oxidation byproducts.     

2‐Methyl‐1,3‐disulfoimidazolium polyoxometalate hybrid catalytic systems as equivalent safer alternatives to concentrated sulfuric acid in nitration of aromatic compounds

Ionic liquid‐derived polyoxometalate salts [mdsim]₃[PM₁₂O₄₀] (where M = W and Mo) of two heteropolyacids H₃PW₁₂O₄₀.nH₂O and H₃PMo₁₂O₄₀.nH₂O were synthesized using 2‐methyl‐1,3‐disulfoimidazolium chloride ([mdsim][Cl]) ionic liquid and the corresponding heteropolyacids. Three equivalents of [mdsim][Cl] were treated with the respective Keggin‐structured heteropolyacids (one equivalent) in aqueous medium at room temperature to afford the water‐stable ionic polyoxometalates as acidic solids. They were completely characterized using spectroscopic and other analytical techniques including thermal analysis and Hammett acidity studies. The inherent Brønsted acidic properties of ─SO₃H group of these polyoxometalate salts were studied for the nitration of aromatic compounds with 69% HNO₃ at normal temperature and 80°C without use of any external concentrated sulfuric acid. These strongly acidic polyoxometalates display good recyclability and efficient reusability.     

Platinized-heteropolycompound-based nanostructured catalysts for low-temperature hydrogen-air fuel cells

Heteropoly acids Cs _x H_{3 − x} PW₁₂O₄₀ · nH₂O with different cesium content are synthesized as nanostructured compositions. Their actual composition and specific surface are determined, microstructure studied and proton conductivity measured. Composite electrocatalytic systems based on platinized cesium salt of phosphorus-tungsten heteropolyacid Cs_2.3H_0.7PW₁₂O₄₀ · nH₂O are prepared with admixture of Vulcan XC-72 carbon black. Mixed electronic-ionic conduction of the composite systems with different carbon black content is studied. Platinum-based nanostructured electrocatalyst based on the Cs_2.3H_0.7PW₁₂O₄₀ · nH₂O-materials as support is synthesized and studied. The possible effective using of the studied nanocomposite as electrode for low-temperature hydrogen-air fuel cells is demonstrated. Electrochemical studies of catalytic properties of the Pt-Cs_2.3H_0.7PW₁₂O₄₀ · nH₂O-C-electrodes in hydrogen and air are carried out by example of the prepared materials with different carbon black content.     

Fabrication of Cs2.5H0.5PW12O40 three-dimensional ordered film by colloidal crystal template

A three-dimensional ordered polyoxometalate periodic film was synthesized using dodecatungstophosphoric acid (H₃PW₁₂O₄₀) and Cs₂CO₃ as precursors and colloidal crystals as templates by an inverse opal method. The samples were characterized by elemental analysis, XRD, IR spectra, UV-Vis diffuse reflectance spectra (DR-UV-Vis) and SEM techniques. This arrayed film constructed by pure cesium salt of dodecatungstophosphoric acid Cs_2.5H_0.5PW₁₂O₄₀ nanoparticles shows well-defined lamellar array with inverse opal structure, which exhibits a well-defined photonic band gap.     

Catalysis by porous heteropoly compounds

This paper attempts to review recent works on catalysis of porous heteropoly compounds. The salts of heteropolyacids having Keggin structure with large cations like Cs⁺ are porous materials. For Cs hydrogen salts, the pore width can be controlled by the Cs content. Cs_2.5H_0.5PW₁₂O₄₀ has the largest amount of protons on the surface among the acidic Cs salts and possesses pores with bimodal distribution in the micro and meso region. Efficient performances were demonstrated for acid-catalyzed reactions such as skeletal isomerization of -butane in solid-gas system, alkylation and acylation in solid-liquid system, and hydrolysis and hydration in solid-water system. A microporous salt, Cs_2.2H_0.8PW₁₂O₄₀, exhibited reactant shape selectivity towards direct decomposition of esters. Furthermore, an ultramicroporous bifunctional catalyst, Pt–Cs_2.1H_0.9PW₁₂O₄₀ of which the pore width is around 5 Å, exhibits reactant shape selectivity for hydrogenation of alkenes and oxidation of hydrocarbons, and product shape selectivity for skeletal isomerization of -butane.     

Mobility of protons in 12-phosphotungstic acid and its acid and neutral salts

The proton mobility in 12-phosphotungstic heteropolyacid (PWA) and its salts (Cs₂HPW₁₂O₄₀·xH₂O, Cs₃PW₁₂O₄₀·xH₂O, (NH₄)₃PW₁₂O₄₀·xH₂O) was investigated by impedance spectroscopy and nuclear magnetic resonance with pulsed field gradient under wide range of relative humidity. Values of two diffusion components observed in PWA as well as in its acid cesium salt differ in one order of magnitude. Also there are two components in the impedance spectra of these compounds. Thus, we suggest, the proton transport take place both inside the grains and along its boundaries. Self-diffusion coefficients, observed in the neutral cesium and ammonium salts, are close to each other and equal to the fast diffusion coefficient in acid cesium salt. At the same time, there is the only relaxation component in the impedance spectra of neutral salts. Thus, it can be concluded, that in case of neutral salts of PWA, there is no proton transport inside the grains of these compounds, and their high proton conductivity caused by fast proton transport along the grain boundaries.     

Electrocatalytic properties of platinum nanocenters electrogenerated at ultra-trace levels within zeolitic phosphododecatungstate cesium salt matrices

A unique preparation method of obtaining stable composite film (with ultra-low platinum content) highly active towards oxygen reduction and hydrogen oxidation is presented here. The matrix for platinum centers consists of high-surface-area zeolite-type acidic salt of cesium phosphododecatungstate (Cs_2.5H_0.5PW₁₂O₄₀) admixed with carbon (Vulcan XC-72) carriers. Platinum nanoparticles were deposited on the working electrode modified with matrix via corrosion of platinum counter electrode during cyclic voltammetry experiment conducted in acid electrolyte containing chloride ions. The results obtained from rotating disk voltammetry revealed that the composite film containing Pt nanoparticles at very low loadings (on the level of 2–5 μg cm^?2) demonstrated remarkable electrocatalytic activity towards both oxygen reduction and hydrogen oxidation, particularly, when compared to the performance of the Cs_2.5H_0.5PW₁₂O₄₀-free system (i.e., containing only Vulcan support) prepared and examined under analogous conditions. The phenomenon should be primarily ascribed to the mesoporous nature of the matrix enabling immobilization and stabilization of small catalytic nanoparticles (1–2 nm diameters) inside the pores as well as to high surface acidity of the polyoxometalate-based salt providing proton-rich environment at the electrocatalytic interface.     

Shape selective oxidation by a microporous platinum-polyoxometalate

Shape selective catalytic behaviour of a platinum-promoted polyoxometalate, 0.5 wt% Pt−Cs_2.1H_{0 9}PW₁₂O₄₀, has been studied for complete oxidation of methane and benzene. The pore size of this catalyst determined by adsorptions of n-butane and isobutane was close to the molecular size of n-butane (0.43 nm). Ar and N₂ porosimetries demonstrated that 0.5 wt% Pt−Cs_{2 1}H_{0 9}PW₁₂O₄₀ possesses unimodal distribution of pores in ultramicropore region. External surface area was estimated to be less than 3% that of the total surface area (61 m² g⁻¹) of the catalyst. Owing to the restricted pores, this exhibited efficient shape selectivity; methane (molecular size; 0.38 nm) was readily oxidized, while the oxidations of the larger molecule such as benzene (0.59 nm) were greatly suppressed. These results indicate that 0.5 wt% Pt−Cs_{2 1}H_{0 9}PW₁₂O₄₀ is a promising microporous catalyst.     

Synthesis of Cs2.5H0.5PW12O40/TiO2 Nanocomposites with Dominant TiO2 {001} Facets and Related Photocatalytic Properties

TiO₂ nanosheets with dominant {001} facets, coupled with Cs_2.5H_0.5PW₁₂O₄₀, were successfully synthesized by a one‐step hydrothermal reaction. The photocatalytic activity of nanocatalysts was evaluated by the degradation of Rhodamine B under UV light irradiation. The results showed that both the addition of Cs_2.5H_0.5PW₁₂O₄₀ and the exposed {001} facets of TiO₂ have a positive effect on the photocatalytic activity. The improved photoactivity of nanocomposites in comparison with that of TiO₂ nanosheets could be attributed to the synergistic effect between Cs_2.5H_0.5PW₁₂O₄₀ and TiO₂ which facilitates the separation of photo‐induced hole‐electron pairs.     

Acidity function of concentrated solutions of 12-tungstophosphoric acid

Conclusions The authors have measured the Hammett acidity functions H₀ of concentrated solutions of H₃PW₁₂O₄₀ in water, aqueous dioxane, and acetic acid. In these solvents the acidity of H₃PW₁₂O₄₀ is higher than those of sulfuric and hydrochloric acids.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 492–493, March, 1982.     

Direct synthesis of dimethyl carbonate ?from CH3OH AND CO2 by H3PW12O40/CexTi1-xO2 catalyst

Summary Ce_xTi_1-xO₂ and H₃PW₁₂O₄₀/Ce_xTi_1-xO₂ catalysts were prepared using a sol-gel method, and applied to the direct synthesis of dimethyl carbonate from methanol and carbon dioxide. H₃PW₁₂O₄₀/Ce_xTi_1-xO₂ showed a better catalytic performance than the corresponding Ce_xTi_1-xO₂, due to the bifunctional catalysis of Br?nsted acid sites (provided by H₃PW₁₂O₄₀) and base sites (provided by Ce_xTi_1-xO₂). H₃PW₁₂O₄₀/Ce_0.1Ti_0.9O₂ showed the highest catalytic performance among the H₃PW₁₂O₄₀/Ce_xTi_1-xO₂ catalysts.     

高选择性和稳定性的CsPW/Nb2O5催化剂用于甘油脱水制备丙烯醛（英文）

以磷钨酸铯盐Cs2.5H0.5PW12O40(CsPW)为活性组分,负载到Nb2O5载体上,并用于甘油脱水制备丙烯醛的反应中.通过调节焙烧温度(400–700°C)以及活性组分负载量(5儃60 wt%),对催化剂酸性进行调节.CsPW负载量为20 wt%,500°C焙烧的CsPW/Nb2O5催化剂性能最佳,甘油转化率为96%,丙烯醛选择性为80%,反应10 h内没有失活现象,并且该催化剂具有良好的热稳定性,可通过烧炭进行再生.     

Catalysis of heteropoly acidic salts for synthesis of diethylene glycol ethyl ether with diethylene glycol and ethanol

Ag₃PW₁₂O₄₀ and Ag₄SiW₁₂O₄₀ showed high activity and stability in the synthesis of diethylene glycol ethyl ether with diethylene glycol and ethanol, on which the conversion is 80.2% and 78.4%, respectively, and the selectivity of diethylene glycol ether is 75.4% and 80.6%, respectively. After the third reaction cycle, Ag₃PW₁₂O₄₀ and Ag₄SiW₁₂O₄₀) still showed higher activity and selectivity, on which the conversion is 72. 6% and 77.5% respectively. But the activity of Ag₃PMo₁₂O₄₀ is lower, the conversion is only 21.0%. IR, XRD, TG and n‐butylamine titrimetry showed that the catalysis may be connected with two kinds of acidic centers owned by heteropoly acidic salt.     

Epoxidation of cycloolefins with hydrogen peroxide in the presence of heteropoly acids combined with phase transfer catalyst

Oxidation of cycloolefins (cyclohexene, cyclooctene, and cyclododecene) with a 30% solution of hydrogen peroxide at 65 °C in the presence of heteropoly acids (HPA) H₃PW_12–x Mo _x O₄₀ (x = 0—12), which are precursors of active peroxo complexes, and phase transfer catalysts Q⁺Cl^–, where Q⁺ is the quaternary ammonium cation containing C₄—C₁₈ alkyl groups or [C₅H₅NC₁₆H₃₃]⁺, was studied. The catalytic activity decreases in the HPA series: H₃PW₁₂O₄₀ > H₃PW₉Mo₃O₄₀ > H₃PW₆Mo₆O₄₀ > H₃PW₃Mo₉O₄₀ > H₃PMo₁₂O₄₀. The state of the H₃PW₁₂O₄₀—I₂I₂ system was studied using UV, IR, and ³¹P NMR spectroscopies with variation of the [H₂O₂] : [HPA] ratio from 2 to 200 during cyclohexene epoxidation. Despite different catalytic precursors, the reaction proceeds through the same peroxo complex.     

Preparation of 1-butyl-3-methylimidazolium dodecatungstophosphate and its catalytic performance for esterification of ethanol and acetic acid

1-Butyl-3-methylimidazolium dodecatungstophosphate catalyst ([bmim]₃PW₁₂O₄₀) with high water tolerance was prepared from 1-butyl-3-methylimidazolium bromide ([bmim]Br) and phosphotungstic acid (H₃PW₁₂O₄₀). The catalyst was characterized by means of Fourier transform infrared spectroscopy, thermogravimetry-differential scanning calorimetry, n-BuNH₂ potentiometric titration, elemental analysis and so on. Its catalytic activity for esterification of ethanol and acetic acid to ethyl acetate was measured. The results show that there were three crystal-water molecules in the [bmim]₃PW₁₂O₄₀ catalyst, and it preserved the primary Keggin structure and acid strength of H₃PW₁₂O₄₀. The acid amount of [bmim]₃PW₁₂O₄₀ catalyst was less than that of H₃PW₁₂O₄₀. The [bmim]₃PW₁₂O₄₀ catalyst exhibited higher catalytic activity and reusability in the esterification of ethanol and acetic acid to ethyl acetate. __________ Translated from Chinese Journal of Catalysis, 2008, 29(7) (in Chinese)     

Oxidation of isobutane catalyzed by vanadyl, copper and cesium substituted H3PMo12O40

Effects of Cs⁺, H⁺ and Cu²⁺ counterions in the vanadium containing heteropoly compounds Cs_xH_1-xVO[PMo₁₂O₄₀] and Cs_yH_0.5-yCu_0.25VO[PMo₁₂O₄₀] on the catalytic oxidation of isobutane and characterization by TGA, IR and ESR spectroscopies are reported. A high selectivity of 76% for methacrylic acid and methacrolein together has been obtained with Cs_0.75H_0.25VO[PMo₁₂O₄₀] catalysts at a reactivity of 5.3x10^-1 mmol/h cm³.