Supported Heteropolyacid Catalysts Research Articles

Production of a Renewable Functionalized 1,3-Diene from Furfural–Acetone Adduct over Supported Heteropolyacid Catalysts

The transformation of renewable feedstocks into high-value chemicals is a sustainable and eco-friendly energy technology. In this work, a functionalized 1,3-diene (1-(2-furyl)-1,3-butadiene, F-dien...

Supported heteropolyacids catalysts for the selective hydrocracking and isomerization of n-C16 to produce jet fuel

In the process of two-stage hydrogenation from bio-oil to jet fuel, the selective cracking and isomerization of long-chain alkanes is the key step. The n-C16 was used as the model reactant to produce jet fuel and the supported metal-acid bifunctional HPA/MCM-41 catalyst was prepared. The acid strength and amount of the catalyst could be modified by adjusting the type (HPW, HSiW, HPMo) and loading of HPA. The highest yield of jet fuel (≈ 20 wt.%) was obtained over Pt/40 wt.% HPMo/MCM-41 (WHSV = 1 h−1), which possessed more B acid sites but few strong acid sites. Besides, it possesses a higher yield than the previous work and favorable catalytic stability of 100 h. It was further explored that the reaction path net of hydrocracking and isomerization of n-C16 was a cascade reaction from n-C16 to single-branched isomer, further to multi-branched isomer and then to the cracking product.

Catalytic Hot-Gas Filtration with a Supported Heteropolyacid Catalyst for Preconditioning Biomass Pyrolysis Vapors

During ex situ catalytic fast pyrolysis (CFP) of biomass, the separation of reactive char and alkali/alkaline particulates from biomass pyrolysis vapors by hot-gas filtration (HGF) leads to improve...

Diels-Alder cycloaddition of oxidized furans and ethylene over supported heteropolyacid catalysts for renewable terephthalic acid

Abstract The Diels-Alder reaction of biomass-derived dimethyl 2,5-furandicarboxylate (DMFDC) with ethylene followed by dehydrative aromatization is a sustainable route for the production of terephthalic acid, a monomer used for the synthesis of polyethylene terephthalate (PET). In this work, a series of heteropolyacid (HPA) catalysts with different supports, in this case SiO2, TiO2 and ZrO2, and hetero-addenda atoms, here phosphotungstic acid (HPW), silicotungstic acid (HSiW) and phosphomolybdic acid (HPMo), were used as catalysts, and their structure-activity correlation in the conversion of DMFDC to terephthalate was examined based on the density and strength of the acid sites. Characterization by XRD and Raman indicated that the Keggin structures of HPAs were well preserved on the SiO2 support compared to other supports, resulting in strong Bronsted acidity. The silica-supported HPW and HSiW catalysts exhibited significantly higher activity for terephthalate production than other supports and HPMo catalysts, but their activity were not correlated with the total acidity as measured by NH3-TPD. In contrast, the catalyst acid strength, as determined by the NH3 desorption temperature, decreased in the order HPW/SiO2 > HSiW/SiO2 >> HPW/ZrO2 > HPW/TiO2 > HPMo/SiO2 and was well correlated with the turnover rate for terephthalate production, suggesting that the higher activity of HPW/SiO2 is at least partly due to its stronger Bronsted acidity and that promoting the dehydration step of this reaction is a key to improving the selectivity to terephthalate. The effects of reaction conditions, in this case the acid loading amount, solvent used, temperature, and time, were also investigated with the most active silica-supported HPW catalysts to optimize the terephthalate yield. The 25%-HPW/SiO2 catalyst demonstrated a remarkable terephthalate yield of ∼60% with almost complete conversion under the optimum condition.

Transformation of dl Limonene into Aromatic Compounds Using Supported Heteropolyacid Catalysts

The transformation of dl limonene (mixture of d- and l-form ~ 1:1) that came from the pyrolysis of scrap tires rubber was studied using four heteropolyacid catalysts (H3PW12O40, H3PMo12O40, H4SiW12O40 and H4PMo11VO40) supported on Q-10, SBA-15, MCM-41, and KIT-6. The catalyst activity was measured using a py/GC/FID under a nitrogen atmosphere. The active phase and support were characterized using various technical methods (XRD, Raman, TEM, N2 adsorption–desorption, NH3-TPD, and py-FTIR). The highest weak acidity and largest number of Lewis acid sites promoted the conversion of dl limonene. The isomerization reactions seemed to be more favored than disproportionation reactions. The p-cymene yield was favored, with a high weak acidity and high Lewis/Bronsted acid sites ratio. Moreover, the results show that the use of amorphous support with a higher pore size seems to promote the conversion of dl limonene and the production of p-cymene. HPA-based catalysts with Si are more favorable for converting dl limonene to p-cymene than those with P. For the HPA-based catalysts with P, the highest acidity favors the highest conversion, especially the Lewis acid sites. In this study, the isomerization reactions seem to be more favored than disproportionation reactions.

The carbonylation of dimethyl ether catalyzed by supported heteropoly acids: The role of Brønsted acid properties

The carbonylation of dimethyl ether (DME) to methyl acetate (MA) is a vital step in a direct route of ethanol production from syngas. Heteropoly acids (HPAs) as a kind of solid acid catalysts can facilitate the reaction. To improve the accessibility of Brønsted acid sites, we prepared a series of supported HPAs catalysts by wetness impregnation on SBA-15. The impact of the HPAs loading and composition on the textural structure and acidic properties was investigated by comparing with the bulk HPAs. Taking acidity analysis (Pyridine-IR and TPD) and catalytic measurement results, we explored the effect of the amount and strength of Brønsted acid site on this reaction. The observations demonstrated that more and stronger acid sites are prone to MA formation.

Highly Efficient Glycerol Acetalization over Supported Heteropoly Acid Catalysts

AbstractThe acetalization of glycerol with acetone to yield solketal was catalyzed by Cs2.5H0.5PW12O40 (Cs2.5) supported on mesoporous silica under mild conditions. It gave a high glycerol conversion and selectivity to the targeted product even at room temperature (23 °C). We studied the use of both bulk and supported Cs2.5 as catalysts in another highly efficient glycerol acetalization reaction with paraformaldehyde, which gave much higher activity than with formaldehyde solution. For the reaction with acetone, the supported Cs2.5 showed a higher activity than the bulk material because of the high surface area of the mesoporous support. Interestingly, the supported Cs2.5 gave a lower conversion than the bulk for the reaction with paraformaldehyde. This is probably because of the high viscosity of the reaction system with the solid reagent paraformaldehyde. Overall, there is a complex relationship between catalyst, reaction conditions, which include the molar ratio of reactants and temperature, reaction mechanism and thermodynamics that affects the achieved activity and byproduct formation. A discussion about these interactions is included for each reaction.

Heteropolyacid catalysts for Diels-Alder cycloaddition of 2,5-dimethylfuran and ethylene to renewable p-xylene

The Diels-Alder cycloaddition of biomass-derived furans and subsequent dehydration are promising routes for the sustainable production of commodity chemicals such as p-xylene (PX). In this paper, we have investigated the catalytic performances of a range of phosphotungstic acid (HPW) and silicotungstic acid (HSiW) catalysts supported on various oxides, i.e., SiO2, Al2O3, TiO2 and ZrO2 and their structure-activity correlation in the conversion of 2,5-dimethylfuran (DMF) and ethylene to PX. The characterization studies of the catalysts using XRD, BET, Raman and 31P MAS-NMR spectroscopy reveal that all of the supported heteropolyacid (HPA) catalysts (except HPW/ZrO2) retain their Keggin structure on the surface of oxide supports. Results from ammonia- and n-propylamine-TPD studies show that all of the supported HPA catalysts possess well-defined Brønsted acid sites with the total acidity decreasing in the following order: HPA/SiO2>HPA/Al2O3>HPA/ZrO2>HPA/TiO2. The conversion of DMF and the initial rate of PX production generally increase with an increase in the total acidity, with HPA/SiO2 being the most active catalyst. The turnover frequency of PX production for HPA/SiO2 is also considerably greater than those for the HPAs supported on Al2O3, ZrO2, and TiO2, which suggests that the higher activity of HPA/SiO2 is at least partly due to the enhanced strength of Brønsted acid sites. Both the silica-supported HSiW and HPW catalysts demonstrate remarkably high PX selectivity (82–85%) at high DMF conversion (91–94%) at 250°C after 6h reaction. The effects of reaction conditions such as acid loading, reaction temperature, and reaction time have also been investigated with the most active silica-supported HSiW catalysts to optimize the PX yield.

SnO2–SiO2 Mesoporous Composite: A Very Active Catalyst for Regioselective Synthesis of Aromatic Ketones with Unusual Catalytic Behavior

Aromatic ketones (R-Ar-CO-R′) have been prepared directly through C–C bond formation using aromatics, aryl, and alkyl acid halides in a Friedel–Crafts reaction over a reusable and catalytically active ordered SnO2–SiO2 three-dimensional mesoporous composite (PS-4) catalyst, which was found to be superior to modified zeolites, functionalized MCM-41, and supported heteropolyacid catalysts.

Preparation, Characterization of Supported Phosphotungstic Acid HPW-MCM-48 and Photocatalytic Degradation of Aqueous Methyl Orange

In this paper, heteropoly acids were supported onto mesopore materials MCM-48 with lager surface area and high thermal stability. The supported heteropoly acids catalysts were characterized by FT-IR, XRD, TEM and N2 adsorption-desorption thechniques. In addition, the effects of supported contents of heteropoly acids on degradation rate also had been researched.

Effect of 3D open-pores on the dehydration of n-butanol to di-n-butyl ether (DNBE) over a supported heteropolyacid catalyst

The production of di-n-butyl-ether (DNBE), for use as a blending agent in diesel fuel, is very attractive because the reactant (n-butanol) can be readily produced by the fermentation of bio-derivatives. The dehydration of n-butanol is known to show diffusion-limited characteristics on porous catalysts, such as zeolites or mesoporous supported catalysts. In order to overcome this limitation, herein, we synthesized silica spheres (DSS) with three-dimensional (3D) open pores by a hydrothermal reaction for use as a catalyst for the dehydration of n-butanol. In addition, supported heteropolyacid (PW) catalysts were also prepared on various porous silicas, DSS, SBA-15 and microporous silica (mi-S), to investigate the effect of 3D pore structures on the conversion of n-butanol to DNBE against 2D mesoporous and microporous materials by quantitative calculation. PW/DSS showed the best performance among the catalysts at various temperatures (453, 473, and 493K). The extent of catalytic performance enhancement was quantified by calculating the effectiveness factor (η) based on kinetics data. The η values for PW/DSS, PW/SBA, and PW/mi-S were determined to be 0.83, 0.63 and 0.52, respectively.

Production of bioadditives from glycerol esterification over zirconia supported heteropolyacids

The synthesis of bioadditives for biofuels from glycerol esterification with acetic acid was performed over zirconia supported heteropolyacids catalysts using H4SiW12O40 (HSiW), H3PW12O40 (HPW) and H3PMo12O40 (HPMo) as active compounds. The as-prepared catalysts were characterized by N2-physisorption, XRD, Raman spectroscopy, NH3-TPD, FTIR of pyridine adsorption and H2O-TPD. Among the catalysts tested, HSiW/ZrO2 achieved the best catalytic performance owing to the better combination of surface Brønsted acid sites and hydrothermal stability. A 93.6% combined selectivity of glyceryl diacetate and glyceryl triacetate with complete glycerol conversion was obtained at 120°C and 4h of reaction time in the presence of HSiW/ZrO2. This catalyst also presented consistent activity for four consecutive reaction cycles, while HPW/ZrO2 and HPMo/ZrO2 exhibited distinct deactivation after reusability tests. In addition, HSiW/ZrO2 can be resistant to the impurities present in bulk glycerol.

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.

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.

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

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.

Direct synthesis of hydrogen peroxide using Au–Pd-exchanged and supported heteropolyacid catalysts at ambient temperature using water as solvent

The direct synthesis of hydrogen peroxide from molecular H2 and O2 represents a green and economic alternative to the current anthraquinone process used for the industrial production of H2O2. In order for the direct process to compete with the anthraquinone process, there is a need for enhanced H2O2 yields and H2 selectivity in the process. We show that Au–Pd-exchanged and supported Cs-containing heteropolyacid catalysts with the Keggin structure are considerably more effective in achieving high H2O2 yields in the absence of acid or halide additives than previously reported catalysts. The Au–Pd-exchanged Cs-heteropolyacid catalysts also show superior H2O2 synthesis activity under challenging conditions (ambient temperature, water-only solvent and CO2-free reaction gas). Au plays a crucial role in achieving the improved performance of these heteropolyacid-based catalysts. The heteropolyacid limits the subsequential hydrogenation/decomposition of H2O2.

ChemInform Abstract: Catalytic Chemistry of Supported Heteropolyacids and Their Applications as Solid Acids to Industrial Processes

AbstractReview: 73 refs.

A Single-Step Solid Acid-Catalyzed Process for the Production of Biodiesel from High Free Fatty Acid Feedstocks

Biodiesel is a nontoxic, renewable, and biodegradable alternative green fuel for petroleum-based diesel. However, the major obstacle for the commercial production of biodiesel is the high cost of raw material, i.e., refined vegetable oils. This problem can be addressed using low-cost feedstocks, such as waste oils and fats. However, these feedstocks contain a high amount of free fatty acids (FFAs), which cannot be used for the production of biodiesel using a traditional homogeneous alkali-catalyzed transesterification process. A solid acid catalyst based on a supported heteropolyacid catalyst (PSA) was evaluated for the production of biodiesel from soybean oil (SBO) containing up to 25 wt % palmitic acid (PA). It was demonstrated that this solid acid catalyst catalyzed simultaneously esterification and transesterification. The total glycerin, ester content, and acid numbers were determined according to ASTM D 6584, EN 14103, and ASTM D 974, respectively. It was found that at 200 °C, 1:27 oil/alcohol molar ratio, and 3 wt % catalyst, a high-quality biodiesel with an ester content of 93.95 mass % was produced from a feedstock (SBO containing 10% PA) in 10 h. The PA and chemically bound glycerin (CBG), which includes triglyceride (TG), diglyceride (DG), and monoglyceride (MG), conversions of 92.44 and 99.38% were obtained, respectively. The effect of process parameters, such as catalyst amount, oil/alcohol molar ratio, and FFA content in the feedstock, has been investigated. This single-step solid acid-catalyzed process has potential for industrial-scale production of biodiesel from high FFA feedstocks.

Heteropoly acids as catalysts for liquid-phase esterification and transesterification

Esterification of hexanoic acid and transesterification of ethyl propanoate and ethyl hexanoate with excess methanol are tested at 60 °C and ambient pressure with a range of heteropoly acid (HPA) catalysts in homogeneous and heterogeneous systems in comparison with conventional acid catalysts such as H 2 SO 4 , Amberlyst-15 and zeolites HY and H-Beta. The turnover frequency of HPA catalysts is significantly higher than that of the conventional acid catalysts in these reactions. Esterification of hexanoic acid and transesterification of ethyl propanoate and ethyl hexanoate with excess methanol (1:20 molar ratio) are tested at 60 °C and ambient pressure with a range of HPA catalysts in homogeneous and heterogeneous systems in comparison with conventional homogeneous and solid acid catalysts such as H 2 SO 4 , Amberlyst-15 and zeolites HY and H-Beta. The intrinsic catalytic activity (turnover frequency, TOF) of HPA catalysts is significantly higher than that of the conventional acid catalysts in these reactions. The TOF values decrease with decreasing catalyst acid strength in the order: H 3 PW 12 O 40 ≈ Cs 2.5 H 0.5 PW 12 O 40 > H 4 SiW 12 O 40 > 15%H 3 PW 12 O 40 /Nb 2 O 5 , 15%H 3 PW 12 O 40 /ZrO 2 , 15%H 3 PW 12 O 40 /TiO 2 > H 2 SO 4 > HY, H-Beta > Amberlyst-15. The activity per unit catalyst weight falls in a different order: H 2 SO 4 > H 3 PW 12 O 40 ≈ H 4 SiW 12 O 40 > Amberlyst-15 ≥ Cs 2.5 H 0.5 PW 12 O 40 > supported H 3 PW 12 O 40 > HY, H-Beta. Bulk cesium salt Cs 2.5 H 0.5 PW 12 O 40 exhibits high catalytic activity as well as high stability to leaching. Supported HPA catalysts suffer from leaching and exhibit significant contribution of homogeneous catalysis by the leached HPA.