UV-visible spectroscopic study of solid state 12-molybdophosphoricacid catalyst

Summary UV-visible spectroscopic studies of solid H₃PMo₁₂O₄₀were carried out to elucidate the effect of crystalline water molecules, and in turn, to provide a guideline for utilizing UV-visible spectra of solids to probe reduction potentials of HPA catalysts. UV-visible spectra of reduced/reoxidized H₃PMo₁₂O₄₀were also measured to check the possibility of utilizing UV-visible spectroscopy as a probe of reduction/oxidation states of H₃PMo₁₂O₄₀catalyst. Absorption edges of solid H₃PMo₁₂O₄₀ shifted to longer wavelength with heating to decrease the number of crystalline water molecules. It was also revealed that UV-visible spectra of the H₃PMo₁₂O₄₀catalyst varied in a systematic way depending on the reduction/oxidation states of the H₃PMo₁₂O₄₀catalyst.</o:p>     

Impregnation of tungstophosphoric acid on poly(methacrylamide-co-methyl methacrylate) and its acid catalytic activity in TMB alkylation

A poly(methacrylamide-co-methylmethacrylate) (abbreviated PMAA-MMA) polymer support was studied for supporting a heteropolyacid (tungstophosphoric acid, H₃PW₁₂O₄₀) with its surface positively charged in the polymerization step. PMAA-MMA supports could be obtained in a porous form by eliminating template reagent molecules (benzylmalonic acid) combined with properly selected monomer (methacrylamide). The amount of amine groups in PMAA-MMA directly determined the amount of H₃PW₁₂O₄₀ impregnated, because the amine groups induced a positive charge on the PMAA-MMA surface. Finally, H₃PW₁₂O₄₀/PMAA-MMA showed better acid catalytic activities than unsupported H₃PW₁₂O₄₀ in alkylation of 1,3,5-trimethylbenzene with cyclohexene, which confirmed that PMAA-MMA supported H₃PW₁₂O₄₀ effectively.     

Synthesis, characterization and photocatalytic application of H3PW12O40/BiVO4 composite photocatalyst

A series of H3PW12O40/BiVO4 composite with different H3PW12O40 loadings were prepared using a hydrothermal and impregnation method. The prepared composites were characterized by XRD, Raman, SEM, XPS, and DRS techniques. The bandgap of the composite was narrower compared with the as-prepared pure BiVO4 . As a novel photocatalytic material, the photocatalytic performance of the H3PW12O40/BiVO4 composite was investigated by the degradation of methylene blue (MB) dye solution under visible light irradiation and compared with that of pure BiVO4 . The results revealed that the introduction of H3PW12O40 could improve the photocatalytic performance and different concentrations of H3PW12O40 resulted in different photocatalytic activities. The highest activity was obtained by the sample with a loading HPW concentration of 10 wt%. The reason for the enhanced photocatalytic activities of H3PW12O40/BiVO4 samples was also discussed in this paper. Moreover, the H3PW12O40/BiVO4 composites retained the catalytic activity after four repeated experiments.     

Acetylation of Alcohols Catalyzed by Dodeca-tungsto(molybdo)phosphoric acid

Summary. Acetylation of primary, secondary, and tertiary alcohols was carried out in some refluxing alkyl acetates and in two carboxylic acids with the participation of catalytic amounts of H₃PW₁₂O₄₀, H₃PMo₁₂O₄₀, and H₁₄P₅W₃₀O₁₁₀ with good yields and high stereo(regio)specificity under mild reaction condition. H₃PW₁₂O₄₀ and H₃PMo₁₂O₄₀ have also shown excellent reactivity in the formylation of 1-butanol with ethyl formate at room temperature and in short reaction times. Heteropolyacid catalysts could be separated after a simple work up and reused for several times.     

Vapor-phase synthesis of ethyltert-butyl ether on heteropoly acid-polymer composite film catalysts

H₃PMo₁₂O₄₀-polysulfone and H₃PMo₁₂O₄₀-polyphenylene oxide composite film catalysts were prepared by a membrane preparation technique. They showed the higher catalytic activities than H₃PMo₁₂O₄₀ in the vapor-phase synthesis of ethyl tert-butyl ether.     

Raman spectra of hybrid materials based on carbon nanotubes and Cs3PMo12O40

A route for the synthesis of hybrid materials using multiwalled carbon nanotubes (MWCNTS) and Cs₃PMo₁₂O₄₀ was confirmed. The Cs₃PMo₁₂O₄₀ salt was synthesized from H₃PMo₁₂O₄₀·14H₂O and CsCl. All compounds were characterized by Raman spectroscopy. The synthesis method can produce a chemically stable Cs₃PMo₁₂O₄₀ molecule and pure and oxidized MWCNTS. Raman spectroscopy showed that the chemical interaction between MWCNTS and Cs₃PMo₁₂O₄₀ was essentially of electrostatic nature. Raman spectra obtained with different wavelengths showed thermal decomposition of H₃PMo₁₂O₄₀·14H₂O (raw materials) from laser heating process. On the contrary, the synthesized compound (i.e. Cs₃PMo₁₂O₄₀) was stable under the experimental conditions.     

Facile preparation of an α-Keggin-type [H3W12O40] complex: Does it exist in aqueous solution?

The formation processes of α-Keggin-type [H₂W₁₂O₄₀]⁶⁻ and [H₃W₁₂O₄₀]⁵⁻ complexes were investigated in aqueous W^VI (0.05–0.50 M) solutions. The formation of [H₂W₁₂O₄₀]⁶⁻ was ascertained by the appearance of a ¹⁸³W NMR line at −117 ppm, but no evidence was found for the existence of [H₃W₁₂O₄₀]⁵⁻ in the solution at the accessible pH range. The addition of (CH₃)₄N⁺ (Me₄N⁺) to the W^VI solution directly precipitated the (Me₄N)₆[H₂W₁₂O₄₀] salt. On the other hand, the addition of the larger Bu₄N⁺ cation precipitates the (Bu₄N)_4.5H_0.5[H₃W₁₂O₄₀] salt, because a naked proton formed during the crystallization process or in the solid state may enter into the Keggin shell to produce [H₃W₁₂O₄₀]⁵⁻. This explanation is based on the fact that [H₂W₁₂O₄₀]⁶⁻ is not spontaneously converted into [H₃W₁₂O₄₀]⁵⁻ in acidified aqueous solution. On the basis of their voltammetric properties, a simple diagnostic criterion was developed to distinguish between [H₂W₁₂O₄₀]⁶⁻ and [H₃W₁₂O₄₀]⁵⁻.     

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.     

Heteropolyacids as new catalysts of the Ritter reaction

Some nitriles reacted with camphene in the presence of heteropolyacids (H₃PW₁₂O₄₀, H₄SiW₁₂O₄₀, H₇PMo₁₂O₄₀) as catalyst to give N-(1,7,7-trimethylbicyclo[2.2.1]hept-2-yl)-substituted amides in fairly high yields.     

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.     

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)     

Keggin-type H4PVMo11O40-based catalysts for the isobutane selective oxidation

Cesium heteropolysalts Cs₃PMo₁₂O₄₀ and HCs₃PVMo₁₁O₄₀ were synthesized by modifying the preparation conditions in order to get materials with a much higher surface area than the original Keggin-type heteropolyacids (H₃PMo₁₂O₄₀ and H₄PVMo₁₁O₄₀). These solids were used as carriers for the dispersion of H₄PVMo₁₁O₄₀ heteropolyacid by the incipient wetness impregnation technique. The textural and structural properties of supports and catalysts were examined by scanning electron microscopy, N₂ adsorption-desorption isotherms and Raman spectroscopy. The supported catalysts were studied before and after red/ox pretreatments by X-ray photoelectron spectroscopy, which showed that both the surface composition and oxidized to reduced species ratio depend on the used carrier. The catalytic performances of these novel supported catalysts in the selective oxidation of isobutane to methacrylic acid and methacrolein were studied. The best catalytic properties were obtained when H₄PVMo₁₁O₄₀ was supported on HCs₃PVMo₁₁O₄₀. The isobutane conversion and yield of the desired oxygenates increased along the unsupported H₄PVMo₁₁O₄₀ < H₄PVMo₁₁O₄₀/Cs₃PMo₁₂O₄₀ < H₄PVMo₁₁O₄₀/HCs₃PVMo₁₁O₄₀ series.

     

Catalysis by heteropolyacids—VIII. Immobilization of keggin-type heteropolyacids on poly(4-vinylpyridine)

Anchoring of a Keggin-type heteropolyacid (HPA) to a polymeric support and the effect of heterogenization on the HPA catalysis of the oxidation of a primary diol have been studied. A coloured HPA such as H₆[Co(II)W₁₂O₄₀] (blue green), H₄[SiMo₁₂O₄₀] (yellow) or H₃[PMo₁₂O₄₀] (yellow), as the Keggin-type HPA and poly(4-vinylpyridine) as a polymeric support have been used. The anchoring of H₆[Co(II)W₁₂O₄₀] has led to a markedly increased stability of the oxidation catalyst.     

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.     

采用溶胶-凝胶-溶剂热路径合成H3PW12O40/TiO2和H4SiW12O40/TiO2 及其光催化降解二硝基甲苯

以非离子表面活性剂P123为结构导向剂,采用溶胶-凝胶与溶解热相结合方法,制备了两类介孔材料H₃PW₁₂O₄₀/TiO₂和H₄SiW₁₂O₄₀/TiO₂,并对其进行了表征.?X射线粉末衍射和拉曼光谱分析表明,所制催化剂为锐钛矿晶型,体系中H₃PW₁₂O₄₀和H₄SiW₁₂O₄₀的Keggin结构经400?℃焙烧后仍保持完整.?H₃PW₁₂O₄₀/TiO₂和H₄SiW₁₂O₄₀/TiO₂的平均粒径分别为15.49和7.75?nm.?N₂吸附-脱附和扫描电镜结果表明,P123的加入使催化剂的粒径减小,比表面积和孔体积明显增大,其中H₃PW₁₂O₄₀/TiO₂和H₄SiW₁₂O₄₀/TiO₂的比表面积分别高达252.2和250.0?m²/g.?紫外漫反射吸收光谱表明,与纯TiO₂相比,复合催化剂的吸收光谱发生了明显的红移,且吸收强度明显增大.?催化剂对DNT降解实验表明,在最佳操作条件下降解率可高达95%.?     

Synthesis of 1,2,9-trisubstituted purin-6(9H)-ones catalyzed by heteropolyacids

1,2,9-Trisubstituted purin-6(9H)-ones have been synthesized in high yield by reaction of 5-amino-N,1-dimethyl-1H-imidazole-4-carboxamide with aromatic aldehydes in the presence of heteropolyacids, H₃PMo₁₂O₄₀ and H₅PV₂Mo₁₀O₄₀. The catalytic activity of H₃PMo₁₂O₄₀ is lower than that of H₅PV₂Mo₁₀O₄₀. This is an effective synthesis of l,2,9-trisubstituted guanine derivatives with the advantages of mild reaction conditions, simple operation, and good yields.     

A Study of the Acid Properties of Structurally and Compositionally Different Heteropoly Acids in Acetic Acid

The acid properties of heteropoly acids of the following three structure types were studied by conductometry in acetic acid: Keggin (H₃PW₁₂O₄₀, H₃PMo₁₂O₄₀, H₄SiW₁₂O₄₀, H₃PW₁₁ThO₃₉; and H₅PW₁₁XO₄₀, where X(IV) = Ti or Zr), Dawson (-H₆P₂W₁₈O₆₂and -H₆P₂Mo₁₈O₆₂), and H₆P₂W₂₁O₇₁(H₂O)₃. These compounds are electrolytes that dissociate in only the first step of this solvent. The thermodynamic dissociation constants of the heteropoly acids were calculated by the Fuoss–Kraus method. The Hammett acidity functions H ₀of the solutions of H₅PW₁₁XO₄₀, H₃PW₁₂O₄₀, H₄SiW₁₂O₄₀, and H₆P₂W₂₁O₇₁(H₂O)₃in 85% acetic acid at 25°C were determined by the indicator method. All of the test heteropoly acids were found to be strong acids.     

双帽Keggin型杂多阴离子[H4As3Mo12O40]-和Keggin型杂多酸H3PM12O40 (M＝Mo, W)质子化的DFT研究

选用B3LYP方法在LanL2MB水平下, 对双帽α-Keggin型杂多阴离子[H₄As₃Mo₁₂O₄₀]^-的电子结构和质子的定位进行了密度泛函理论(DFT)研究. 结果表明, 双帽的形成大大影响了杂多阴离子[As₃Mo₁₂O₄₀]^5－的电子结构和性质, NBO分析显示参与成帽的三桥氧上的电子密度比双桥氧上的要大, 简单地从电荷密度来看, 质子将首先在三桥氧上定域成键, 但通过比较质子定域在几种桥氧上质子化稳定化能的大小, 发现[H₄As₃Mo₁₂O₄₀]^-中的四个质子将在八个双桥氧中的其中四个氧原子上定位, 而不是如文献中报道的在四个三桥氧上定域成键. 对杂多酸H₃PM₁₂O₄₀ (M＝Mo, W)中质子的定位也进行了理论计算并与文献进行了比较, 结果显示, H₃PMo₁₂O₄₀中质子是定位在双桥氧上; 而H₃PW₁₂O₄₀中质子将优先在双桥氧上定位, 但也可在端氧上定位; 这一结果与文献报道的相一致.     

The Catalytic Performance of Preyssler's Anion, [NaP5W30O110]14−, in the Oxidation of Benzyl Alcohols

Under mild conditions, monosubstituted benzyl alcohols were oxidized to benzaldehydes and benzoic acids in the presence of sodium 30-tungstopentaphosphate (Preyssler's anion), [NaP₅W₃₀O₁₂₀]^14? , and hydrogen peroxide as an oxidant. This polyanion with high hydrolytic stability (pH = 0–12), high thermal stability, and high acidic strength shows good activities. The effects of various parameters on the yield of the products, including a catalyst type, a nature of the substitutents, and temperature, were studied. Comparison between Keggin's heteropolyacids, H₃[PW₁₂O₄₀], H₃[PMo₁₂O₄₀], H₄[SiW₁₂O₄₀], and H₄[SiMo₁₂O₄₀], and Preyssler's anion shows that this polyanion reacts similar to Keggin's acids whitout any degradation of the structure.     

Boehmite nano‐particles functionalized with silylpropylamine‐supported Keggin‐type heteropolyacids: Catalysts for epoxidation of alkenes

Boehmite nano‐particles with a high degree of surface hydroxyl groups were covalently functionalized by 3‐(trimethoxysilyl)‐propylamine to support H₃[PMo₁₂O₄₀], H₃[PW₁₂O₄₀], H₄[SiMo₁₂O₄₀] and H₄[SiW₁₂O₄₀] Keggin‐type heteropolyacids. After characterization of these catalysts by FT‐IR, powder X‐ray diffraction, TG/differential thermal analysis, CHN, inductively coupled plasma and transmission electron microscopy techniques, they were applied to the epoxidation of cis‐cycloocten. The progress of the reactions was investigated by gas–liquid chromatography, and the catalytic procedures were optimized for the parameters involved, such as the solvent and oxidant. The results showed that 25 mg of supported H₃[PMo₁₂O₄₀] catalyst in 1 ml C₂H₄Cl₂ with 0.5 mmol cyclooctene and 1 mmol tert‐butylhydroperoxide at reflux temperature gave 98% yield over 15 min. Recycling experiments revealed that these nanocatalysts could be repeatedly applied up to five times for a nearly complete epoxidation of cis‐cycloocten. The optimized experimental conditions were also used successfully for the epoxidation of some other alkenes, such as cyclohexene, styrene and α‐methyl styrene.