Heteropolyacid Catalysts Research Articles

Transesterification of waste cooking oil by heteropoly acid (HPA) catalyst: Optimization and kinetic model

Transesterification of waste cooking oil with heterogeneous (heteropoly acid) catalyst and methanol has been investigated. Response Surface Methodology (RSM) and Artificial Neural Network (ANN) were employed to study the relationship between process variables and free fatty acid conversion and for predicting the optimal parameters. The highest conversion was 88.6% at optimum condition being 14h, 65°C, 70:1 and 10wt% for reaction time, reaction temperature, methanol to oil molar ratio and catalyst loading, respectively. The RSM and ANN could accurately predict the experimental results, with R2=0.9987 and R2=0.985, respectively. Kinetics studies were investigated to describe the system. The reaction followed first-order kinetics with the calculated activation energy, Ea=53.99kJ/mol while the pre-exponential factor, A=2.9×107min−1. These findings can help improve an environmentally friendly biodiesel process that conforms to ASTM D6751 standards.

Optimization of biodiesel production process from Jatropha oil using supported heteropolyacid catalyst and assisted by ultrasonic energy

Application of ultrasound-assisted biodiesel production process from Jatropha oil catalyzed by activated carbon-supported tungstophosphoric acid catalyst was studied. Influences of ultrasonic energy on different process variables were elucidated. Reaction variables i.e. reaction time (10-50 min), reactants' molar ratio (5:1-25:1), ultrasonic amplitude (30-90% of the maximum sonifier power) and catalyst amount (2.5-4.5 w/w oil) were studied. A mathematical representation for biodiesel yield was successfully generated. A yield of 91% was achieved in just 40 min at a moderate ultrasonic amplitude (similar to 60%), high molar ratio (25:1) and low reaction temperature (65 degrees C). Interactions between the variables were also validated statistically. Leaching study revealed that the reaction was predominately heterogeneous in nature. (C) 2012 Elsevier Ltd. All rights reserved.

One-Pot Synthesis of 1-Benzoylpyrene over Heteropoly Acid Catalysts

A novel one-pot catalytic synthesis of 1-benzoylpyrene through acylation of pyrene with benzoyl chloride catalyzed by various Keggin type heteropoly acids (salts) was investigated. Pure 1-benzoylpyrene was obtained and the structure of 1-benzoylpyrene was identified by GC/MS, FT-IR and 1H NMR spectra. H3PW12O40 (PW) was found to be the most active catalyst in the acylation. The yield and the selectivity of 1-benzoylpyrene were up to 97.6 % and 100 %, respectively. The effects of experimental parameters on the catalytic acylation reaction and the recycling performance of PW catalyst were studied. PW catalyst shows well catalytic activity after running for 5 times. The facile product separation and the recycling performance of PW catalyst is expected to contribute to the development of clean and environmentally friendly strategy for the synthesis of 1-benzoylpyrene.

Compensation effect in isopropanol dehydration over heteropoly acid catalysts at a gas–solid interface

Kinetics of isopropanol dehydration at a gas–solid interface over a range of bulk and supported Brønsted acid catalysts based on H3PW12O40 (HPW) Keggin-type heteropoly acid was studied in a continuous flow fixed-bed reactor in the temperature range of 55–135°C and isopropanol partial pressure of 0.94–5.52kPa. The bulk catalysts included HPW itself and its Cs acid salts CsnH3−nPW12O40 (CsnH3−nPW). The supported catalysts comprised of 15wt.% HPW supported on SiO2, TiO2, ZrO2 and Nb2O5. Under the conditions studied, the reaction was found to be of zero order in isopropanol. The turnover rate decreased in the order HPW>Cs2.5H0.5PW≈Cs2HPW>HPW/SiO2>HPW/TiO2>HPW/Nb2O5≈HPW/ZrO2, which is in line with the acid strength of these catalysts. The true activation energies E and pre-exponential factors A obtained from zero-order kinetics, were found to exhibit a compensation linear relationship lnA=mE+c. Moreover, the bulk and supported catalysts exhibited different compensation plots. This is suggested to be due to the different chemical structure of Brønsted acid sites in these catalysts, resulting in differing reaction mechanisms. The bulk catalysts possess strong surface H+ sites located on peripheral (bridging) oxygen atoms in the Keggin unit, whereas supported HPW catalysts have weaker H+ sites probably located on oxygen atoms of support. Consequently, on the bulk catalysts, isopropanol dehydration is suggested to occur via E1 elimination pathway, whereas on the supported catalysts it might also involve a contribution of E2 elimination pathway.

Catalytic Synthesis of Fused 1,4-Dihydropyridines and 1,4-Dihydropyridine Derivatives Using Preyssler Heteropolyacids Catalyst

An efficient and convenient method for the synthesis of 1,4-dihydropyridines from β-dicarbonyl compounds, aldehydes, and ammonium acetate and the synthesis of fused 1,4-dihydropyridines from dimedone in the presence of Preyssler heteropolyacid catalyst are reported under reflux conditions with good to excellent yields. Preyssler heteropolyacid catalyst is easily prepared, stable (up to 300 °C), reusable, efficient, green and inexpensive.

Amino-containing cross-linked ionic copolymer-anchored heteropoly acid for solvent-free oxidation of benzyl alcohol with H2O2

Abstract Amino-containing cross-linked ionic copolymer-anchored HPA catalysts were prepared by the anion-exchange of polydivinylbenzene/amino-functionalized ionic liquids copolymers with Keggin heteropoly acid (HPA), and were characterized by 1H NMR, FT-IR, TG, XRD, SEM, TEM, BET surface area, and elemental analysis. Their catalytic performance for oxidation of benzyl alcohol with H2O2 was studied under solvent-free conditions. The results demonstrated that the catalysts were very active and selective, and could be reused after simple separation.

Hydrolysis of Dimethyl Ether over Heteropoly Acids Catalyst

Heteropoly acide(HPA), as one kind of solid-super acid catalysts, has been researched and applied extensively. Using SBA-15 and ZSM-5 as carriers, HPA catalysts with different types and contents were applied in this work for the hydrolysis of dimethyl ether(DME). It had been found that ZSM-5 was a proper carrier, and its supported phosphotungstic acid exhibited relatively high catalytic activity in this low-temperature hydrolysis reaction.

Scanning Tunneling Microscopy Study of Nano-Structured Polyatom-Substituted H4PW11M1O40 Keggin and H7P2W17M1O62 (M = Nb, Ta) Wells-Dawson Heteropolyacid Catalysts

Polyatom-substituted H4PW11M1O40 Keggin and H7P2W17M1O62 (M = Nb, Ta) Wells-Dawson heteropolyacid (HPA) catalysts were investigated by scanning tunneling microscopy (STM) and tunneling spectroscopy to elucidate their redox property and oxidation catalysis. STM images clearly showed that HPAs formed nano-structured monolayer arrays on graphite surface. In tunneling spectroscopy, HPAs exhibited a distinctive current-voltage behavior called negative differential resistance (NDR). NDR peak voltage of the HPAs was then correlated with reduction potential determined by electrochemical method in solution. NDR peak voltage of the HPAs appeared at less negative voltage with increasing reduction potential. Vapor-phase oxidative dehydrogenation of isobutyraldehyde to methacrolein was also carried out as a model reaction to probe oxidation catalysis of the HPAs. NDR peak voltage of the HPAs appeared at less negative voltage with increasing yield for methacrolein. NDR peak voltage could be utilized as a correlating parameter for the reduction potential and as a probe of oxidation catalysis in the oxidative dehydrogenation of isobutyraldehyde.

Selective Synthesis of Glycerol Monoester with Heteropoly Acid as a New Catalyst

In this work, we were study the selective synthesis of GME from oleic acid and glycerol using two types of solid heteropoly acid catalysts, namely silicotungstic acid bulk (STAB) and STA-silica sol gel (STA-SG). The performance and selectivity of STAB and STA-SG in the esterification reaction have been investigated and compared to the sulphuric acid (H2SO4) as conventional homogeneous catalyst. The catalysts were then characterized their physical and chemical properties using BET, XRD, TEM and XPS. XPS analyses were shown 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 in terms of the relatively lower pH value (pH 3.7) than the STAB (pH 2.8). 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 H2SO4 and 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.

Simulation of Cumene Synthesis by Suspension Catalytic Distillation

This paper deals with alkylation of benzene with propylene to produce cumene by Suspension Catalytic Distillation (SCD) which, as a new technology of process intensification, has been developed from traditional catalytic distillation. In this SCD process, the supported heteropolyacid catalysts are suspended inside the liquid phase on the column tray and flow with them, while in traditional catalytic distillation the catalyst pellets are generally fixed somewhere inside the column. SCD processes have been investigated for alkylation reaction of benzene with olefins in laboratorial scale. A pilot plant of SCD process for cumene synthesis had been run for several months. It has shown more advantageous characteristics for cumene synthesis compared with conventional process consisting of a reactor followed by distillation train. Based on experimental data and the reactive kinetic parameters of cumene synthesis using the supported heteropolyacid catalysts, numerical simulation of SCD process of the pilot plant was performed by an equilibrium stage model to study the effects of operation conditions on the process performance. The simulation results could agree, to a great extent, with the data acquired from the pilot plant experiment.

Etherification of n-butanol to di-n-butyl ether over HnXW12O40 (X Co2+, B3+, Si4+, and P5+) Keggin heteropolyacid catalysts

Etherification of n-butanol to di-n-butyl ether was carried out over heteroatom-substituted HnXW12O40 (XCo2+, B3+, Si4+, and P5+) Keggin heteropolyacid (HPA) catalysts. Acid properties of HPA catalysts were determined by NH3-TPD measurements. Acid strength of HnXW12O40 Keggin HPA catalysts increased in the order of H6CoW12O40 < H5BW12O40 < H4SiW12O40 < H3PW12O40. Yield for di-n-butyl ether increased with increasing acid strength of the catalysts. Acid strength of HPAs served as an important factor determining the catalytic performance in the etherification of n-butanol to di-n-butyl ether.

Research Progress in the Direct Synthesis of Dimethyl Carbonate from CO2 and Methanol

The direct synthesis of dimethyl carbonate (DMC) from CO2 and methanol is one attractive way for the reduction of greenhouse gas emission and the utilization of carbon resources. Recent progress in the direct synthesis of DMC from CO2 and methanol is reviewed with the focus on the catalyst systems, including organic metal compounds catalyst, base catalyst, acetate catalyst, metal oxide and supported metal oxide catalysts, heteropolyacid catalyst and photocatalyst. Moreover, the application of supercritical system, ionic liquid system, electrochemical system, membrane reactor and nitriles hydration in the direct synthesis of DMC are also introduced. Finally, future research direction in this area is proposed.

Preparation and Photocatalytic Activity of Heteropoly Acids/Polyvinylidene Fluoride Thin Films

In this paper, catalysts of (NH4)4SiW12O40 supported on polyvinylidene fluoride(PVDF) thin films were prepared and characterized by IR and SEM.In addition,sunlight as the light source and simulation of dyes effluent (malachite green) as the research object, through the orthogonal experiments studied the factors that influence catalyst photocatalytic degradation effects,such as the amount of catalyst, pH, the amount of hydrogen peroxide . The results show that the degradation of malachite green of the heteropoly acid catalyst immobilized by membrane is best under the conditions of visible and achieve high degradation rate( 90% ). Also , the catalytic effect is also related with the oxidant dosage and the acidity. The catalyst is energy saving, easy recovery and has widest foreground.

Aqueous Solutions of Mo‐V‐Phosphoric Heteropoly Acids as Bifunctional Catalysts For Preparation of 9,10‐Anthraquinone and its Hydrogenated Derivatives

AbstractAcid‐catalyzed condensation of 1,3‐butadiene with para‐quinones and oxidation of resulting adducts can be performed as a one‐pot process in the presence of aqueous solutions of Mo‐V‐phosphoric heteropoly acids (HPA) with the general formula HaPzMoyVxOb. These solutions have bifunctional catalytic properties; they are both strong Brønsted acids and reversible oxidants. Condensation of hydroquinone, 1,4‐benzoquinone, or 1,4‐naphthoquinone with 1,3‐butadiene in the HPA solutions results in 9,10‐anthraquinone (AQ) in a mixture with tetrahydro‐AQ (THA) and dihydro‐AQ (DHA). In this one‐pot process, which proceeds in the absence of organic solvents, the HPA solution is reduced. A slightly soluble mixture of THA, DHA, and AQ is precipitated and filtered off. The non‐Keggin‐type H12P3Mo18V7O85 solution is the most effective in this process. This solution can be rapidly regenerated by dioxygen or air at temperatures of up to 170 °C and then reused. The prepared THA+DHA+AQ mixture can be used as a catalyst for alkaline delignification of wood. Our homogeneous bifunctional HPA catalyst is very stable and promising for use in similar one‐pot processes.

Heteropolyacid catalyzed conversion of fructose, sucrose, and inulin to 5-ethoxymethylfurfural, a liquid biofuel candidate

The heteropolyacid H3PW12O40 has been used as a catalyst for the production of 5-ethoxymethylfurfural (EMF), a viable liquid biofuel, from fructose, sucrose, and inulin. An EMF yield of 65% can be obtained from fructose within 30min at 130°C in ethanol under microwave heating. The introduction of tetrahydrofuran as a co-solvent improved the yield of EMF to 76%. Longer reaction time, higher reaction temperature and higher catalyst amount lead to the decomposition of EMF to ethyl levulinate. The fructose moieties in sucrose and inulin are converted to EMF selectively. However, glucose moieties cannot be converted to EMF by this heteropolyacid catalyst. Instead ethyl glucoside is formed.

Oxidative ring-opening of 2-methylcyclohexanone catalysed by supported heteropolyacid catalysts for cetane number enhancement

Incipient wetness impregnation method was used to incorporate heteropolyacid H6[PV3Mo9O40]nH2O (HPA) on SiO2 at various HPA loadings (10, 20, 30, 40 wt.% HPA) and calcined temperatures. Catalytic activity of these synthesised catalysts were evaluated through oxidation of 2-methylcyclohexanone to methyl 6-oxoheptanoate which was a desired product. In the oxidative conditions the conversion and selectivity of the desired product methyl 6-oxoheptanoate can reach as high as 97 and 94 wt.%, respectively. The results also suggested that the catalyst with 20 wt.% loading of HPA to be the best one. The catalysts were characterised using a variety of techniques including XRD, BET, FT-IR and TGA-DTA. The results indicated that HPA was well dispersed on the SiO2 supporting material. An engine ignition test following ASTM D6890 standard indicated that the oxidative ring-opening of cyclohydrocarbons can have a positive impact on the cetane numbers and ignition delay time of fuels. © 2012 Canadian Society for Chemical Engineering

Multi-functionality of cationic porphyrin-immobilized polymeric microspheres prepared by synchronously synthesizing and immobilizing pyridylporphyrin on surfaces of polymeric microspheres

Pyridylporphyrin (PyP) was synchronously synthesized and immobilized on the surfaces of crosslinked polystyrene microspheres (CPS microspheres) via an Adler reaction between solid–liquid phases, resulting in PyP-immobilized microspheres, PyP-CPS microspheres. Then the cationic porphyrin-immobilized microspheres, MPyP-CPS microspheres (“M” represents methyl group that comes from iodomethane), was prepared via the quaternization reaction of PyP-CPS microspheres with iodomethane as reagent. In the current work, the efficiency of the above route to immobilize pyridylporphyrin PyP on CPS microspheres was first researched by a comparison method, and then the multi-functionality of the cationic porphyrin-immobilized microspheres MPyP-CPS were mainly tested and examined from many aspects. The investigation results show that: (1) the above route to immobilize pyridylporphyrin on the surfaces of CPS microspheres is highly efficient, and the immobilization amount of PyP on CPS microspheres can get up to about 0.2 mmol g−1; (2) the cationic porphyrin-immobilized microspheres MPyP-CPS are a kind of multifunctional polymeric microspheres because of their special surface structure, and they can be used to construct different host-guest systems, resulting in many applications. MPyP-CPS microspheres can used as triphase-transfer catalysis in organic synthesis, can coordinate to transition metal ion to form immobilized metalloporphyrin catalysts to be used in the green catalytic oxidations, can be used as support of heteropoly acid to prepare heterogenous heteropoly acid catalyst, and MPyP-CPS microspheres also can used as solid adsorbent in the removal of toxic chromate ion from water medium. In a word, the polymeric microspheres supporting cationic porphyrin, MPyP-CPS microspheres, will have vast application prospect in various fields because they have special surface chemical structure.

Capturing Coke Precursors in a Pd Lattice: A Carbon‐Supported Heteropoly Acid Catalyst for the Dehydration of Glycerol into Acrolein

AbstractSupported heteropoly acid catalysts are frequently used in the dehydration of glycerol into acrolein because of their high activity. However, they are easily deactivated by coke that can become deposited on the catalyst surface. Herein, we report a technique that significantly decreases coke formation by capturing coke precursors in a Pd lattice. The Pd‐added H3PW12O40/C catalyst (Pd‐PWC) showed stable catalytic activity and the amount of deposited coke formed was decreased to about 40 % of that without Pd addition. The catalysts were characterized by XRD, HR‐TEM, XPS, NH3‐TPD, and TGA methods. These results showed that the palladium lattice on the carbon support was easily loosened and that coking precursors were incorporated into the Pd lattice of the catalyst under the reaction conditions used. Consequently, the amount of coke that was deposited onto the active sites of the catalysts was significantly decreased.

Regeneration of Silica‐Supported Silicotungstic Acid as a Catalyst for the Dehydration of Glycerol

The dehydration reaction of glycerol to acrolein is catalyzed by acid catalysts. These catalysts tend to suffer from the formation of carbonaceous species on their surface (coking), which leads to substantial degradation of their performances (deactivation). To regenerate the as-deactivated catalysts, various techniques have been proposed so far, such as the co-feeding of oxygen, continuous regeneration by using a moving catalytic bed, or alternating between reaction and regeneration. Herein, we study the regeneration of supported heteropolyacid catalysts. We show that the support has a strong impact on the thermal stability of the active phase. In particular, zirconia has been found to stabilize silicotungstic acid, thus enabling the nondestructive regeneration of the catalyst. Furthermore, the addition of steam to the regeneration feed has a positive impact by hindering the degradation reaction by equilibrium displacement. The catalysts are further used in a periodic reaction/regeneration process, whereby the possibility of maintaining long-term catalytic performances is evidenced.

Keggin형 H3+xPW12-xNbxO40(x=0, 1, 2, 3) 및 Wells-Dawson형 H6+xP2W18-xNbxO62(x=0, 1, 2, 3) 헤테로폴리산 촉매를 이용한 n-Butanol로부터 Di-n-Butyl Ether의 제조

Keggin형 <TEX>$H_{3+x}PW_{12-x}Nb_xO_{40}$</TEX>(x=0, 1, 2, 3) 및 Wells-Dawson형 <TEX>$H_{6+x}P_2W_{18-x}Nb_xO_{62}$</TEX>(x=0, 1, 2, 3) 헤테로폴리산(Heteropolyacid) 촉매를 이용하여 n-Butanol의 에테르화(Etherification) 반응을 통한 Di-n-Butyl Ether의 제조를 수행하였다. 먼저 Niobium이 서로 다른 비율로 치환된 Keggin형 및 Wells-Dawson형 헤테로폴리산 촉매를 제조하였다. FT-IR, ICP-AES 및 <TEX>$^{31}P$</TEX> NMR 분석을 통하여 촉매가 잘 제조되었음을 확인하였다. <TEX>$NH_3$</TEX>-TPD(Temperature-Programmed Desorption) 분석을 통해 헤테로폴리산 촉매의 산특성을 측정하였다. 두 계열의 촉매군에서 헤테로폴리산 촉매는 Niobium의 함량에 따라 다른 산특성을 나타내었다. 이후, 헤테로폴리산 촉매를 에테르화 반응에 적용하고 촉매의 반응활성과 산특성 간의 상관관계를 분석하였다. Keggin형 <TEX>$H_{3+x}PW_{12-x}Nb_xO_{40}$</TEX> 및 Wells-Dawson형 <TEX>$H_{6+x}P_2W_{18-x}Nb_xO_{62}$</TEX> 헤테로폴리산 촉매의 Acidity는 Keggin형과 Wells-Dawson형 모두에서 Niobium의 치환량이 증가함에 따라 감소하였으며, n-Butanol의 전환율과 Di-n-Butyl Ether로의 수율은 헤테로폴리산 촉매의 구조와 관계없이 Acidity가 증가함에 따라 선형적으로 증가하였다. 이처럼 헤테로폴리산의 Acidity는 n-Butanol의 에테르화(Etherification) 반응을 통한 Di-n-Butyl Ether의 제조 반응에서 촉매 활성을 결정하는 중요한 요소로 작용하였다. Etherification of n-butanol to di-n-Butyl Ether was carried out over Keggin <TEX>$H_{3+x}PW_{12-x}Nb_xO_{40}$</TEX> (x=0, 1, 2, 3) and <TEX>$H_{6+x}P_2W_{18-x}Nb_xO_{62}$</TEX> (x=0, 1, 2, 3) Wells-Dawson heteropolyacid catalysts. Niobium-substituted Keggin and Wells-Dawson heteropolyacid catalysts with different niobium content were prepared. Successful preparation of the catalysts was confirmed by FT-IR, ICP-AES, and <TEX>$^{31}P$</TEX> NMR analyses. Their acid properties were determined by <TEX>$NH_3$</TEX>-TPD (Temperature-Programmed Desorption) measurements. Heteropolyacid catalysts showed different acid properties depending on niobium content in both series. The correlation between acid properties of heteropolyacid catalysts and catalytic activity was then established. Acidity of Keggin and Wells-Dawson heteropolyacid catalysts decreased with increasing niobium content, and conversion of n-butanol and yield for di-n-butyl ether increased with increasing acidity of the catalysts, regardless of the identity of heteropolyacid catalysts (without heteropolyacid structural sensitivity). Thus, acidity of heteropolyacid catalysts served as an important factor determining the catalytic performance in the etherification of n-butanol to di-n-Butyl Ether.