Heteropolyacid Catalysts Research Articles

Fabrication of micellar heteropolyacid catalysts for clean production of monosaccharides from polysaccharides

A micellar heteropolyacids (HPAs) catalyst had been prepared using surfactant cetyltrimethyl ammonium bromide (CTAB) and H 3 PW 12 O 40 as precursors. These micellar [C 16 H 33 N(CH 3 ) 3 ] x H 3 − x PW 12 O 40 had been characterized to be micellar structure and the catalytic activity was evaluated by the hydrolysis of polysaccharides to the reducing sugars. The best catalytic activity was obtained over [C 16 H 33 N(CH 3 ) 3 ]H 2 PW 12 O 40 (abbreviated as (C 16 TA)H 2 PW), which showed 100% conversion and 99.6% selectivity within 60 min at 80 °C for hydrolysis of sucrose. And it was also active for the conversion of starch and cellulose. The leaching test showed that the HPA micellar catalysts have an excellent stability and can be used as heterogeneous catalysts for six times. ► Assembly of HPAs into micellar system with Brønsted acidity. ► Overcoming the diffusion in solid-solid reactions and promoting the reaction rate. ► Easily handing of this catalyst and could be reused about six times.

Preparation of H<sub>5</sub>PMo<sub>10</sub>V<sub>2</sub>O<sub>40</sub> /SBA-15 Catalyst and Application in Synthesis of Tributyl Citrate

The heteropoly acid catalyst of H5PMo10V2O40 supported on SBA-15 mesoporous mole-cular sieve was prepared by an impregnation method and characterized by nitrogen physisorption, FT-IR,SEM, and used in catalytic synthesis of tributyl citrate. The results show that the heteropoly acid catalyst has fine dispersion characteristics, structural stability, high catalytic activity and better reusability.

Gas phase dehydration of glycerol catalyzed by rutile TiO 2-supported heteropolyacids

Gas phase dehydration of glycerol catalyzed by the rutile TiO 2-supported heteropolyacids was investigated. The TiO 2-supported heteropolyacid catalysts were prepared by the incipient wetness impregnation method using silicotungstic, phosphotungstic, and phosphomolybdic acids as active compounds. The as-prepared catalysts were characterized by X-ray diffraction, infrared spectroscopy, temperature programmed desorption of ammonia, and surface area measurement. The heteropolyacids supported by rutile TiO 2 were crystallites. The catalytic activity of the catalysts in the gas phase dehydration of glycerol was significantly affected by the type and loading of heteropolyacids. TiO 2-supported silicotungstic acid (20 wt.%) catalyst showed the highest catalytic activity with an acrolein selectivity of 80 mol% at a conversion of glycerol of 99% and a reaction temperature of 280 °C under ambient pressure. The possible reaction route in the gas phase dehydration of glycerol catalyzed by the TiO 2-supported heteropolyacid catalysts was also discussed briefly.

Catalytic decomposition of benzyl phenyl ether to aromatics over cesium-exchanged heteropolyacid catalyst

Cesium-exchanged Cs x H3.0−x PW12O40 (X=2.0–3.0) heteropolyacid catalysts were prepared and applied to the decomposition of benzyl phenyl ether to aromatics. Benzyl phenyl ether was chosen as a lignin model compound for representing α-O-4 bond in lignin. Phenol, benzene, and toluene were mainly produced by the decomposition of benzyl phenyl ether. Conversion of benzyl phenyl ether and total yield for main products (phenol, benzene, and toluene) were closely related to the surface acidity of Cs x H3.0−x PW12O40 (X=2.0–3.0) heteropolyacid catalyst. Conversion of benzyl phenyl ether and total yield for main products increased with increasing surface acidity of the catalyst. Among the catalysts tested, Cs2.5H0.5PW12O40 with the largest surface acidity showed the highest conversion of benzyl phenyl ether and total yield for main products.

Scanning Tunneling Microscopy Study of H6+x P2Mo18−x V x O62 (x = 0–3) Wells–Dawson Heteropolyacid Catalysts: Correlation of NDR Peak Voltage with Reduction Potential and Oxidation Catalysis

Scanning tunneling microscopy (STM) and tunneling spectroscopy studies were carried out to examine the redox properties of vanadium-containing H6+x P2Mo18−x V x O62 (x = 0, 1, 2, 3) Wells–Dawson heteropolyacid (HPA) catalysts. The HPAs formed two-dimensional well-ordered monolayer arrays on a graphite surface and exhibited a distinctive current–voltage behavior called negative differential resistance (NDR). The NDR peak voltages of H6+x P2Mo18−x V x O62 HPAs were correlated with reduction potentials determined by temperature-programmed reduction and with catalytic activity for oxidative dehydrogenation of isobutyraldehyde to methacrolein. The NDR peak voltage of H6+x P2Mo18−x V x O62 appeared at less negative voltage with increasing reduction potential and oxidation catalysis. Negative differential resistance (NDR) peak voltage of H6+x P2Mo18−x V x O62 determined by scanning tunneling microscopy appeared at less negative voltage with increasing reduction potential and with increasing oxidation catalysis.

High selective production of 5-hydroymethylfurfural from fructose by a solid heteropolyacid catalyst

A clean, facile, economical, and environmental friendly method for converting fructose into 5-hydroymethylfurfural (HMF) has been developed, in the presence of a solid heteropolyacid Cs2.5H0.5PW12O40 catalyst in a biphasic system. A 5-HMF yield of 74.0% and a higher selectivity of 94.7% were obtained in 60min at 388K. More importance is that this catalyst is tolerant to high concentration feedstocks (50wt.% fructose) and it can be recycled.

Hydrolysis of Cellulose over CsxH3–xPW12O40 (X = 1–3) Heteropoly Acid Catalysts

AbstractA series of insoluble heteropolytungstate salts, CsxH3–xPW12O40 (x = 1–3), were prepared and applied to the selective hydrolysis of microcrystalline cellulose to sugars in the aqueous phase. CsxH3–xPW12O40 were active toward the hydrolysis of cellulose into total reducing sugars (TRS) and glucose, which are the important products for the application for biofuels. The conversion of cellulose and total yield for the main products increased with increasing acidity of the catalyst. Cs1H2PW12O40 exhibited the best catalytic activity in terms of the conversion of cellulose and yields for TRS and glucose, while Cs2.2H0.8PW12O40 showed the highest selectivity for TRS and glucose.

ATR-FTIR Study of the Decomposition of Acetic Anhydride on Fosfotungstic Wells–Dawson Heteropoly Acid Using Concentration-Modulation Excitation Spectroscopy

The decomposition of acetic anhydride in liquid phase on a fosfotungstic Wells–Dawson heteropoly acid (HPA) was investigated by in situ ATR-FTIR spectroscopy. Transient and concentration-modulation excitation spectroscopy (MES) experiments in combination with phase-sensitive detection (PSD) were used to monitor the solid–liquid interface. The MES method is based on the periodic variation of a parameter of the reaction media such as, the reactant concentration. That periodic alteration causes varying infrared signals of the surface adsorbed species that are subsequently demodulated with the PSD methodology. Thus, the separation of the static signals from the changing ones is achieved, and species with different response can be observed in the spectra. Using MES-PSD coupled with ATR-FTIR, acetic anhydride was observed to decompose to acetic acid, acetate and acyl [CH3C(O)+] species, involving Bronsted acid sites of the HPA catalyst. The CH3C(O)+ is a very unstable intermediate species and it is the key intermediate in the Friedel–Crafts acylation reactions. Moreover, the acetate groups are spectator species since remain strongly adsorbed on the catalyst surface and do not further react.

Catalytic Hydrothermal Depolymerization Technology and Kinetics of DGEBA/EDA Epoxy Resin

Depolymerization of thermosetting epoxy resin with environmental-friendly heteropolyacid catalyst at temperatures between 270°C-350°C in H2O medium. The effect of the factors catalyst, temperature and time on the depolymerization was researched. UV spectrum was used to characterize the thermal stability of heteropolyacid catalyst. The products of depolymerization were analysed qualitatively and quantitatively by means of GC/MS and GC. The results indicated that the main depolymerized products were phenol, p-isopropylphenol and bisphenol-A (BPA). The results showed adding heteropolyacid contribute to enhancing the rate of depolymerization and increasing the yield of BPA. Also, the depolymerization kinetics of epoxy resin was researched and the activation energy was calculated.

Activated clay supported heteropoly acid catalysts for esterification of acetic acid with butanol

The esterification of acetic acid with primary ( n-), secondary ( sec-) and tertiary ( ter-) butanol catalyzed by supported heteropoly acids (HPAs), such as dodecatungstophosphoric acid (TPA), dodecatungstosilicic acid (TSA) and dodecamolybdophosphoric acid (MPA) on acid activated Bentonite (AT-GMB) matrix have been carried out. The 20% loaded TPA on AT-GMB showed the highest catalytic activity. The conversions of different alcohols into the corresponding esters decrease in the following order: n-butanol > sec-butanol > ter-butanol. The selectivities for the corresponding esters are nearly 100%. The catalysts were characterized by surface area, thermal analysis, XRD and FTIR spectroscopy. The reusability study shows that the catalysts are stable and active.

Reduction potential, UV–visible absorption edge energy, and oxidation catalysis of niobium-containing H 3+ xPW 12− xNb xO 40 Keggin and H 6+ xP 2W 18− xNb xO 62 Wells-Dawson heteropolyacid catalysts

Niobium-containing H 3+ x PW 12− x Nb x O 40 ( x = 0, 1, 2 and 3) Keggin and H 6+ x P 2W 18− x Nb x O 62 ( x = 0, 1, 2 and 3) Wells-Dawson heteropolyacids (HPAs) were prepared in this work to explore their redox properties and oxidation catalysis. Reduction potentials and absorption edge energies of H 3+ x PW 12− x Nb x O 40 and H 6+ x P 2W 18− x Nb x O 62 HPA catalysts were measured by an electrochemical method and UV–visible spectroscopy, respectively. The trend of reduction potential is well consistent with the trend of absorption edge energy with respect to niobium substitution in both series of H 3+ x PW 12− x Nb x O 40 and H 6+ x P 2W 18− x Nb x O 62 HPA catalysts. Absorption edge energy of H 3+ x PW 12− x Nb x O 40 and H 6+ x P 2W 18− x Nb x O 62 HPA catalysts shifted to lower value with increasing reduction potential of the HPA catalysts, regardless of the identity of HPA catalysts; an HPA catalyst with higher reduction potential exhibited lower absorption edge energy. In order to probe oxidation catalysis of H 3+ x PW 12− x Nb x O 40 and H 6+ x P 2W 18− x Nb x O 62 HPA catalysts, vapor-phase benzyl alcohol oxidation was carried out as a model reaction. Yield for benzaldehyde increased with increasing reduction potential and with decreasing absorption edge energy of H 3+ x PW 12− x Nb x O 40 and H 6+ x P 2W 18− x Nb x O 62 HPA catalysts.

Catalytic synthesis of warfarin acetals by using different heteropolyacid catalysts

Catalytic synthesis of warfarin acetals by using different heteropolyacid catalysts In this research, we report on the synthesis of warfarin acetals by using Preyssler's anion, [NaP5W30O110]-14 and heteropolyacids (HPAs) catalysts. This reaction was performed using methanol and ethanol at reflux temperature conditions. Under these conditions we have excellent yields and high selectivity. Preyssler heteropolyacid catalyst were easily recycled recovery and reused without the loss of its catalytic activities. The synthesis of warfarin acetals has been achieved using the catalytic amounts of green, inexpensive and eco-friendly Keggin types heteropolyacids. The products were obtained in high yields.

Synthesis, Characterization and Catalytic Performance ofH3SiW12O40/SiO2Prepared by Sol-Gel Technique

The purpose of this work is to study the synthesis, characterization, and catalytic performance of two types of solid heteropoly acid catalysts, namely, silicotungstic acid bulk (STAB) and STA-silica sol-gel (STA-SG) compared with sulfuric acid. From the XPS analyses, there was a significant formation of W-O-Si, W-O-W, and Si-O-Si bonding in STA-SG compared to that in STAB. The main spectra of O1s (90.74%, 531.5 eV) followed by other O1s peak (9.26%, 532.8 eV) were due to the presence of W-O-W and W-O-Si bonds, respectively. The STA-SG catalyst was found to be the more environmentally benign solid acid catalyst for the esterification reaction between oleic acid and glycerol due to its lower toxicity supported by silica via sol-gel technique. In addition, the ease of separation for STA-SG catalyst was attributed to its insoluble state in the product phase. The esterification products were then analysed by FTIR and HPLC. Both the H2SO4and the STAB gave high conversion of 100% and 98% but at a lower selectivity of GME with 81.6% and 89.9%, respectively. On the contrary, the STA-SG enabled a conversion of 94% but with a significantly higher GME selectivity of 95%, rendering it the more efficient solid acid catalyst.

Screening of Supports and Additives for Heteropoly Acid Catalysts for Friedel-Crafts Reaction by High-throughput Screening and Data Mining

Friedel-Crafts alkylations are very important reactions which are widely used in the production of fine chemicals, intermediates, and petrochemicals. Solid catalysts should be developed for greening of these chemical processes. We previously developed a high-throughput screening system (HTS) and had been screening solid catalysts for benzylation of anisole by benzyl alcohol. In the present study, supports and additives for 12 tungstophosphoric acid (HPA) catalysts were screened by HTS and data mining tools using principal component analysis, radial basis function network, and support vector machine. These methods identified Re-HPA/activated carbon with the highest activity, which was experimentally confirmed.

One pot production of 5-hydroxymethylfurfural with high yield from cellulose by a Brønsted–Lewis–surfactant-combined heteropolyacid catalyst

A Brønsted-Lewis-surfactant-combined heteropolyacid (HPA) Cr[(DS)H(2)PW(12)O(40)](3) has been synthesized, and is used as a heterogeneous catalyst for the conversion of cellulose to 5-hydroxymethylfurfural in one pot within 2 h at 150 °C with 77.1% conversion and 52.7% yield. This micellar HPA catalyst shows stability and can be recycled by simple separation process.

Catalytic Performance of Heteropolyacids as Efficient and Eco-Friendly Catalysts for the One-Pot Synthesis of Benzopyran Derivatives

An efficient and improved procedure for the synthesis of benzopyran derivatives has been achieved with Keggin-type and Preyssler-type heteropolyacids (HPA) catalysts in one-pot reaction under solvent-free conditions.

Preparation, characterization, and oxidation catalysis of H3PMo12O40 heteropolyacid catalyst immobilized on carbon aerogel

Carbon aerogel (CA) with high surface area and large pore volume was prepared by polycondensation of resorcinol with formaldehyde. The surface of CA was then modified to have a positive charge, and thus to provide a site for the immobilization of H3PMo12O40 (PMo12) catalyst. By taking advantage of the overall negative charge of [PMo12O40]3−, PMo12 catalyst was chemically immobilized on the surface-modified CA as a charge matching component. It was found that PMo12 catalyst was finely dispersed on the CA support via chemical interaction. In the vaporphase 2-propanol conversion reaction, the PMo12/CA catalyst showed a higher 2-propanol conversion than the unsupported PMo12 catalyst. Furthermore, the PMo12/CA catalyst showed an enhanced oxidation catalytic activity (formation of acetone) and a suppressed acid catalytic activity (formation of propylene and isopropyl ether) compared to the unsupported PMo12 catalyst. The enhanced oxidation activity of PMo12/CA catalyst was due to fine dispersion of [PMo12O40]3− on the CA support formed via chemical immobilization.

Catalytic hydrothermal depolymerization of nylon 6

Depolymerization of nylon 6 to produce e-caprolactam using an environmentally friendly heteropoly acid catalyst was studied at temperatures between 553 and 603 K in water. The products of depolymerization were analyzed qualitatively and quantitatively by means of mass spectrometry and high-performance liquid chromatography. The results showed that the depolymerized product was mainly e-caprolactam with a little 6-aminocaproic acid and oligomers. The phosphotungstic heteropoly acid used as a catalyst can improve the hydrolysis rate and yield of e-caprolactam. The optimum hydrolysis conditions for e-caprolactam yield were as follows: phosphotungstic heteropoly acid content, 3%; reaction temperature, 573 K; and reaction time, 85 min. Under these conditions, the yield of e-caprolactam was 77.96%. In the temperature range 553–603 K, the activation energy of 3% phosphotungstic heteropoly acid-catalyzed depolymerization was evaluated as 77.38 kJ/mol, which is lower than the 86.64 kJ/mol value for no catalyst.

α-Pinene isomerisation over heteropoly acid catalysts in the gas-phase

The isomerisation of α-pinene was studied in the gas phase over solid heteropoly acid (HPA) catalysts in a fixed-bed continuous flow reactor at 200 °C and ambient pressure. The catalysts included bulk and SiO 2-supported H 3PW 12O 40 and bulk Cs 2.5H 0.5PW 12O 40 possessing strong Brønsted acid sites, as well as composites prepared by supporting 15 wt% H 3PW 12O 40 on Nb 2O 5, ZrO 2 and TiO 2 possessing both Brønsted and Lewis acid sites of moderate strength. The reaction yielded camphene as the main product in a mixture with monoterpene by-products such as limonene, terpinolenes, terpinenes, β-pinene, p-cymene and others. The HPA catalysts with strong Brønsted acid sites exhibited high initial activities, but suffered from catalyst deactivation, resulting in low camphene yields. Conversely, the HPA catalysts supported on Nb 2O 5, ZrO 2 and TiO 2, although weaker acids, showed more stable performance in α-pinene isomerisation. The HPA catalyst supported on TiO 2 gave a camphene yield of 51% and a total camphene and limonene yield of 58%.

Solid acid catalysts based on H 3PW 12O 40 heteropoly acid: Acid and catalytic properties at a gas–solid interface

Solid acid catalysts prepared by supporting 15 wt%H 3PW 12O 40 heteropoly acid (HPA) on TiO 2, ZrO 2 and Nb 2O 5 with a sub-monolayer HPA coverage were characterised at a gas–solid interface, regarding their acid properties and chemical structure of HPA on the catalyst surface and compared to “standard” HPA catalysts such as bulk and silica-supported H 3PW 12O 40 and Cs 2.5H 0.5PW 12O 40. In contrast to the parent acid, H 3PW 12O 40, possessing strong Brønsted acid sites, the catalysts supported on TiO 2, ZrO 2 and Nb 2O 5 have both Brønsted and Lewis acid sites, with the latter mainly originating from the oxide support. The strength of acid sites in these catalysts is weaker than that in H 3PW 12O 40 and Cs 2.5H 0.5PW 12O 40. The catalytic activity (turnover frequency) in gas-phase isopropanol dehydration decreases in the order: H 3PW 12O 40 > Cs 2.5H 0.5PW 12O 40 > 15%H 3PW 12O 40/SiO 2 > 15%H 3PW 12O 40/TiO 2 > 15%H 3PW 12O 40/Nb 2O 5 > 15%H 3PW 12O 40/ZrO 2, which is in line with the acid strength as determined by NH 3 adsorption calorimetry. Ammonia adsorption calorimetry, 31P{ 1H} MAS NMR and FTIR indicate increasing interaction between support and HPA in the following order of supports: SiO 2 < TiO 2 < Nb 2O 5 < ZrO 2.