Heteropolyacid Catalysts Research Articles

Deactivation study of a heteropolyacid catalyst for glycerol dehydration to form acrolein

Gas-phase glycerol dehydration to form acrolein over a heteropolyacid catalyst has been studied to understand the rapid deactivation process. The decrease in the conversion as a function of time was observed depending on operating conditions. The experiments were performed in an isothermal fixed bed reactor for eight hours. The influence of temperature, residence time, glycerol concentration, water concentration and oxygen concentration was studied. Next, a global kinetic equation for the deactivation was proposed for the studied experimental conditions.

Single-step synthesis of 4-phenyl and 3,4-dihydro-4-phenyl coumarins using a recyclable Preyssler heteropolyacid catalyst under solvent-free reaction conditions

Fil: Escobar Caicedo, Angelica Maria. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico la Plata. Centro de Investigacion y Desarrollo En Ciencias Aplicadas; Argentina

Catalytic oxidative desulfurization of benzothiophene using silica-supported heteropolyacid catalyst: activity, deactivation and regeneration of the catalyst

A series of silica-supported heteropolyacid catalysts were prepared by the hydrothermal dispersion and ultrasonic impregnation methods, using phosphotungstic acid as active component and HMS molecular sieve as support. The catalytic stability of catalysts in the oxidative desulfurization of benzothiophene has been investigated. The results show that the sulfur removal of the two catalysts decreased from 97.81 and 95.63 to 81.28 and 75.3 % after eight cycles. The fresh and spent catalysts were characterized by Fourier transform infrared spectra, N2 adsorption, X-ray diffraction and transmission electron microscopy. The main results indicate that the deactivation process of the catalysts went through two stages, i.e., the dissolution of active component is the main factor at prophase and the adsorption of N-hexadecane and sulfone is the primary reason at anaphase. Furthermore, the former is an irreversible deactivation and the latter is a reversible deactivation which can be regenerated by solvent extraction.

Transformation of 5-Hydroxymethylfurfural (HMF) to Maleic Anhydride by Aerobic Oxidation with Heteropolyacid Catalysts

Developing novel technologies to utilize renewable biomass as the source of energy and carbon to partially replace the fossil resources has been well recognized by the global governments and both industrial and academic communities. This work explored a catalytic transformation of biomass-based 5-hydroxymethylfurfural to maleic anhydride and maleic acid through aerobic oxidation with vanadium-substituted heteropolyacid. Under the optimized conditions, total yields of 64% for maleic anhydride and maleic acid could be achieved. Mechanistic studies with control experiments excluded 2, 5-furandicarboxylic acid, 2, 5-diformylfuran, 5-formyl-2-furancarboxylic acid, and 5-hydroxymethyl-2-furancarboxylic acid as the intermediates in the pathway of 5-hydroxymethylfurfural oxidation to maleic anhydride. Alternatively, a new mechanism initialized by the C–C bond cleavage between the hydroxymethyl group and furan sketch of HMF by heteropolyacid has been proposed for MA formation, in which several intermediates have b...

Heteropolyacids as anode catalysts in direct alkaline sulfide fuel cell

Development of economical anode catalysts with satisfactory effectiveness and stability is essential for the practical application of a promising sulfide-fed fuel cell platform, named direct alkaline sulfide fuel cell (DASFC). In this study, heteropolyacids (HPAs), such as phosphomolybdic acid (H3PMo12O40, HPMo), phosphotungstic acid (H3PW12O40, HPW), and silicotungstic acid (H4SiW12O40, HSiW), were examined as potential candidates suited for such purpose. Physical and electrochemical properties of HPA catalysts were evaluated using X-ray diffraction (XRD), Fourier-transformed infrared spectroscopy (FT-IR), energy dispersive X-ray (EDX) analysis, I–V analysis, and electrochemical impedance spectrophotometry (EIS). All HPAs exhibited catalytic activity toward sulfide oxidation at alkaline conditions, recording maximum power densities of 31.34 mW cm−2, 21.18 mW cm−2, and 30.53 mW cm−2 for HPMo, HPW, and HSiW, respectively. 10 h life test did not result in appreciable drop in cell performance, ensuring the stability of HPAs in alkaline sulfide fuel. HPAs, with superb catalytic activity and stability, appear to be potent anode catalysts for the DASFC application.

Oxidative-extractive deep desulfurization of gasoline by functionalized heteropoly acid catalysts

An Anderson-type heteropoly acid catalyst with IMo6O245− is applied for oxidative-extractive desulfurization, and the oxidation and the extraction are performed simultaneously.

TiO2-supported heteropoly acid catalysts for dehydration of methanol to dimethyl ether: relevance of dispersion and support interaction

TiO2-supported heteropoly acids are very active catalysts for DME production from methanol. Due to the interaction with the support, the most active catalysts are obtained when a monolayer of HPA is deposited on the support.

The comparison of two classes of bifunctional SBA-15 supported platinum–heteropolyacid catalysts for the isomerization of n-hexane

SBA-15 supported bifunctional acidic HSiW–Pt catalysts proved to be active, stable and highly selective in the isomerization of n-hexane.

Conversion of highly concentrated fructose into 5-hydroxymethylfurfural by acid–base bifunctional HPA nanocatalysts induced by choline chloride

A series of acid–base bifunctional heteropolyacids (HPAs) (C6H15O2N2)3−xHxPW12O40 (abbreviated as Ly3−xHxPW) have been designed using different ratios of HPAs with amino acid lysine in order to control their acid–base properties. The amino acid group facilitated the HPAs forming micellar assemblies in choline chloride–fructose deep eutectic solvents. In the dehydration of fructose to 5-hydroxymethylfurfural (HMF), Ly3−xHxPW exhibited different catalytic activities because of their different acid–base properties. Among all the HPA catalysts, Ly2HPW gave the best results with 93.3% conversion and 92.3% HMF yield within a very short time, i.e. 1 min under the conventional temperature of 110 °C using choline chloride (ChCl) as solvent, and this was almost the best result by far. The highest activity and selectivity of Ly2HPW came from the synergistic effect between certain acidic and basic capacities, which provides ready accessibility to the nucleophilic (–NH2) and electrophilic (H) sites. Moreover, this catalyst was tolerant to highly concentrated feedstock (∼66.7 wt%) with the additive ChCl. Ly2HPW performed as a heterogeneous catalyst in the ChCl system and could be recycled by simple washing treatment.

Isomerization and Alkylation of Biomass-Derived Compounds in Aqueous Media over Hydrophobic Solid Acid Catalysts: A Mini Review

Isomerization and alkylation of biomass-derived compounds are key industrial processes for mitigating over dependence on fossil fuels and petrochemicals. Although designing the reactions in aqueous media is environmentally sustainable, cost-effective, and efficient, the most reliable catalysts are still being sought. We have therefore reviewed and analyzed classified literature on the prospects of hydrophobic zeolites, acidic oxides, and heteropoly acid catalysts. Emphasis was given to catalyst design, key active sites, modification, catalytic activity in related reactions, and stability properties.

Hydroxylation of Benzene to Phenol by H2O2 over an Inorganic–Organic Dual Modified Heteropolyacid

Various catalysts, including the heteropolyacid (HPA) H4PMo11VO40, its cesium salts, and inorganic–organic dual modified HPA catalyst, were prepared and characterized by Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance (13C NMR), N2 adsorption, acid–base titration, electron spin resonance (ESR) and X-ray diffraction (XRD) techniques as well as elemental analysis. These prepared catalysts were used in the hydroxylation of benzene to phenol by H2O2 as oxidant. The inorganic–organic dual modified HPA Cs2.5(MIMPS)1.5PMo11VO40, prepared by partially exchanging Cs+ with protons in H4PMo11VO40 and followed by the immobilization of 3-(1-methylimidazolium-3-yl)propane-1-sulfonate (MIMPS), led to a liquid–solid biphasic catalysis system in the hydroxylation, which showed the best catalytic performance in terms of reusability and catalytic activity. The high reusability of Cs2.5(MIMPS)1.5PMo11VO40 in the heterogeneous hydroxylation was probably due to its high resistance in leaching of bulk HPA into the reaction medium. The slightly enhanced catalytic activity for the catalyst was due to the acid sites available from MIMPS beneficial to the hydroxylation.

Dehydration of ethanol over heteropoly acid catalysts in the gas phase

Dehydration of ethanol was studied at a gas–solid interface over a wide range of solid Brønsted acid catalysts based on Keggin-type heteropoly acids (HPAs) in a continuous flow fixed-bed reactor in the temperature range of 90–220°C focussing on the formation of diethyl ether (DEE). The catalysts included H3PW12O40 (HPW) and H4SiW12O40 (HSiW) supported on SiO2, TiO2, Nb2O5 and ZrO2 with sub-monolayer HPA coverage, as well as bulk acidic Cs salts of HPW (Cs2.5H0.5PW12O40 and Cs2.25H0.75PW12O40) and the corresponding core–shell materials with the same total composition (15%HPW/Cs3PW12O40 and 25%HPW/Cs3PW12O40, respectively) comprising HPW supported on the neutral salt Cs3PW12O40. The ethanol-to-DEE reaction was found to be zero order in ethanol in the range of 1.5–10kPa ethanol partial pressure. The acid strength of catalysts was characterised by ammonia adsorption microcalorimetry. A fairly good correlation between the catalyst activity (turnover frequency) and the catalyst acid strength (initial enthalpy of ammonia adsorption) was established, which demonstrates that Brønsted acid sites play important role in ethanol-to-DEE dehydration over HPA catalysts. The acid strength and the catalytic activity of core–shell catalysts HPW/Cs3PW12O40 did not exceed those of the corresponding bulk Cs salts of HPW with the same total composition, which contradicts the literature claims of the superiority of the core–shell HPA catalysts.

Electrochemical and UV–visible spectroscopy studies of K6As2W18 − xMoxO62 (x = 0–3) Wells–Dawson heteropolyacid catalysts for oxidative dehydrogenation of benzyl alcohol

Redox behaviors of molybdenum-substituted Wells–Dawson tungstoarsenate heteropolyacid catalysts (α-K6As2W18−xMoxO62 (x=0–3)) were probed by electrochemical and UV-visible spectroscopy measurements. Reduction potential of K6As2W18−xMoxO62 (x=0–3) catalysts shifted to more positive potential with increasing molybdenum content. UV–visible spectroscopy analysis was conducted as a simple diagnostic method for reduction potential. Absorption edge energy determined by UV–visible spectroscopy decreased with increasing reduction potential. Gas-phase oxidative dehydrogenation of benzyl alcohol was carried out as a model reaction. Yield for benzaldehyde increased with increasing electrochemical reduction potential and with decreasing UV–visible absorption edge energy of the catalysts.

Catalytic Synthesis of 2-(1-Cyclohexenyl)cyclohexanone by Mixed Heteropoly Acids Catalyst (PW12 + PMo12/SBA-15)

Catalytic Synthesis of 2-(1-Cyclohexenyl)cyclohexanone by Mixed Heteropoly Acids Catalyst (PW12 + PMo12/SBA-15)

Deep oxidative desulfurization of dibenzothiophene with molybdovanadophosphoric heteropolyacid-based catalysts

Three hydrophobic Keggin-type heteropolyacid catalysts, [C3H3N2(CH3)(C2H4)]5PMo10V2O40 ([C2mim]PMoV), [C3H3N2(CH3)(C4H8)]5PMo10V2O40 ([C4mim]PMoV) and [C3H3N2(CH3)(C6H12)]5PMo10V2O40 ([C6mim]PMoV), were synthesized by reacting molybdovanadophosphoric acid with imidazolium bromides, and characterized by spectroscopic methods. Their use as catalysts in the extractive catalytic oxidative desulfurization process using hydrogen peroxide as the oxidant and acetonitrile as phase transfer agent was studied. The catalytic properties decreased in the order: [C6mim]PMoV > [C4mim]PMoV > [C2mim]PMoV. The main factors influencing the rate of removal of dibenzothiophene (DBT) were investigated, including reaction temperature, the amounts of catalyst, H2O2 and acetonitrile. Nearly 100 % sulfur removal rate was achieved under optimal conditions. The catalyst could be recycled six times with only a slight decrease in activity. A reaction mechanism for DBT oxidation is proposed, in which the Keggin anions first obtain active oxygen from H2O2, then the DBT is oxidized to dibenzothiophene sulfones.

Synthesis, Characterization, and Properties of a New Type of Heteropoly Acids and Supramolecular Compounds

In this article, the method of stepwise acidification, gradually charging and ion exchange was employed for synthesizing tungsten vanadium aluminum heteropoly acid catalysts and heteropoly acids-glycine supramolecules. These novel products were further characterized through chemical analysis, IR, UV-Vis absorbance spectra, and X-ray diffraction analysis. The catalytic properties of these supramolecules were tested and prove the superior catalytic activity than most existing heteropoly acids.

Etherification of <I>n</I>-Butanol to Di-<I>n</I>-Butyl Ether Over Keggin-, Wells-Dawson-, and Preyssler-Type Heteropolyacid Catalysts

Etherification of n-butanol to di-n-butyl ether was carried out over various structural classes of heteropolyacid (HPA) catalysts, including Keggin- (H3PW12O40), Wells-Dawson- (H6P2W18O62), and Preyssler-type (H14[NaP5W30O110]) HPA catalysts. Successful formation of HPA catalysts was well confirmed by FT-IR, 31P NMR, and ICP-AES analyses. Acid properties of HPA catalysts were determined by NH3-TPD (temperature-programmed desorption) measurements. Acid strength of the catalysts increased in the order of H14[NaP5W30O110] < H6P2W18O62 < H3PW12O40. The catalytic performance of HPA catalysts was closely related to the acid strength of the catalysts. In the etherification of n-butanol to di-n-butyl ether over various structural classes of HPA catalysts, Conversion of n-butanol and yield for di-n-butyl ether increased with increasing acid strength of HPA catalysts. Among the catalysts tested, Keggin-type (H3PW12O40) HPA catalyst with the strongest acid strength showed the best catalytic performance. Acid strength of HPAs served as an important factor determining the catalytic performance in the etherification of n-butanol to di-n-butyl ether.

Heterogeneous reusable catalyst, ultrasound energy, and no solvent: a quick and green recipe for one-pot synthesis of β-phosphonomalononitriles at room temperature

Clay-supported heteropolyacid catalyst has been prepared and investigated as a novel heterogeneous, reusable and efficient catalyst for the one-pot synthesis of β-phosphonomalononitriles under ultrasound irradiation at room temperature. Compared with traditional methods, the present method is solvent-free, works under milder and cleaner conditions, furnishes products with higher purity and yields, needs shorter reaction time, easier work-up procedure, and generates less waste. No column purification is required and the products can be purified by simple crystallization. The catalyst can be easily recovered and reused several times without significant loss of its catalytic activity. The catalyst was characterized by scanning electron microscopy, X-ray powder diffraction, and thermal gravimetric, surface area, and elemental analyses.

Preparation and Application of P-Mo-W Heteropoly Acid Catalyst

the phosphorus-molybdenum-tungsten heteropoly acid catalyst is prepared from such raw materials as phosphoric acid, sodium molybdate, sodium tungstate and characterized by infrared spectrum. Glyoxylic acid is prepared by catalytic oxidation of glyoxal in the presence of the self-prepared heteropoly acid catalyst and oxidizing agent hydrogen peroxide. The impact of catalytic reaction temperature, added catalyst, and use level of the hydrogen peroxide on the reaction for synthesizing the glyoxylic acid is investigated. The results show under such conditions as 4°C temperature, 0.15g catalyst, and 1.2:1 molar ratio of the hydrogen peroxide to the glyoxal, the phosphorus-molybdenum-tungsten heteropoly acid catalyst has higher catalytic activity and the mass fraction of the glyoxylic acid is 30%.

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.