Use Of Heteropolyacids Research Articles

Esterification of enzymatically treated macaw palm oil catalyzed by heteropolyacid supported onto Nb2O5

An approach to producing biodiesel is the esterification of free fatty acids with an acyl acceptor. Free fatty acids can be produced through the hydrolysis of acylglycerols and represent a somewhat challenging feedstock for the production of biodiesel due to slower kinetics and the production of water in the reaction. The purpose of this work was to demonstrate the feasibility of a Keggin-structured heteropolyacid, H3PW12O40 (HPW) supported onto Nb2O5 to be used as a catalyst for the reaction of free fatty acids with ethanol to produce ethyl esters that comply with biodiesel norm values. The use of heteropolyacids as heterogeneous catalysts may present advantageous operational benefits, including the tolerance to residual water present in the medium and the potential for reusability. The catalyst was prepared via impregnation of HPW onto Nb2O5 and was characterized in terms of acidity and surface properties. The enzymatic hydrolysis of macaw palm oil yielded a feedstock containing a free fatty acid content greater than 93%. The hydrolysate was assessed as a reactant for the esterification reaction, evaluating temperature, molar ratio, and catalyst amount, leading to optimal conversions greater than 99% with viscosity and density within the regulatory limits for biodiesel. The use of heterogeneous acid catalysts, such as HPW/Nb2O5, represents a potentially feasible alternative to unlocking the potential of working with challenging feedstocks as oil hydrolysates.

Trends in Widely Used Catalysts for Fatty Acid Methyl Esters (FAME) Production: A Review

The effective transesterification process to produce fatty acid methyl esters (FAME) requires the use of low-cost, less corrosive, environmentally friendly and effective catalysts. Currently, worldwide biodiesel production revolves around the use of alkaline and acidic catalysts employed in heterogeneous and homogeneous phases. Homogeneous catalysts (soluble catalysts) for FAME production have been widespread for a while, but solid catalysts (heterogeneous catalysts) are a newer development for FAME production. The rate of reaction is much increased when homogeneous basic catalysts are used, but the main drawback is the cost of the process which arises due to the separation of catalysts from the reaction media after product formation. A promising field for catalytic biodiesel production is the use of heteropoly acids (HPAs) and polyoxometalate compounds. The flexibility of their structures and super acidic properties can be enhanced by incorporation of polyoxometalate anions into the complex proton acids. This pseudo liquid phase makes it possible for nearly all mobile protons to take part in the catalysis process. Carbonaceous materials which are obtained after sulfonation show promising catalytic activity towards the transesterification process. Another promising heterogeneous acid catalyst used for FAME production is vanadium phosphate. Furthermore, biocatalysts are receiving attention for large-scale FAME production in which lipase is the most common one used successfully This review critically describes the most important homogeneous and heterogeneous catalysts used in the current FAME production, with future directions for their use.

Synthesis and Characterization of a Novel Heteropoly Acid/Hydrogel Composite

Catalysis by Heteropoly acids (HPAs) and polyoxometalates (POMs) having a higher demand worldwide, as it can be designed to accelerate complex reactions and be more environmentally friendly. However, recycling of water-soluble solid catalysts remains a problem. The synthesis of a recyclable composite with catalytic properties is the key to better use of HPAs and POMs. Many researches have mentioned the method of synthesis by immersing a porous carrier in a supported solution. However, the catalytic stabilities of the previously studied composites after multiple uses have rarely been mentioned. In this research, a novel idea is proposed to synthesize a heteropoly acid supported composite. A complex hydrogel with catalytic properties was synthesized by mixing an anionic monomer with a heteropoly acid. The heteropoly acid particles were inserted inside the hydrogel by the interaction forces between the anions. Thus, preventing the water-soluble heteropoly acid from being lost during the catalytic reaction. The complex hydrogel is consisted of the anionic monomer 2-acrylamide-2methylpropanesulfonic acid (AMPS) as a carrier, N,N’-Methylenebisacrylamide (MBAA) as crosslinkers and the typical Keggin-type HPA: H3PW12O40. At last, a composite with (NH4)3PW12O40 particles was synthesized.

Preparation of K8[Cu(H2O)W11CrO39]@rGO-CeO2 nanocomposite and its photodegradation of Rhodamine B

K8[Cu(H2O)W11CrO39]@rGO-CeO2 nanocomposite, a new ternary composite material, was synthesized by dip-molding method, and characterized by FT-IR, XRD, UV–Vis, N2-adsorption, SEM and EDS. In order to evaluate photocatalytic degradation activity of this nanocomposite, Rhodamine B (RhB) solution was selected as the reaction model of photocatalytic and the influences of initial concentration, pH, catalyst dosage, and different catalysts on photocatalytic performance were investigated under ultraviolet light irradiation (λ < 400 nm). The results show that the degradation rate of RhB reached 97.83% under the condition when initial concentration was 5 mg/L, pH 2, and the catalyst dosage at 0.10 g. The nanocomposite as catalyst for photocatalytic experiments exhibited an enhanced photocatalytic performance due to the synergic effect between heteropoly acid (HPA) and rGO-CeO2 NPs. Our present findings will have a profound effect on the use of HPA@ rGO-CeO2 nanocomposite as photocatalytic material.

Promoted V2O5/TiO2 catalysts for selective catalytic reduction of NO with NH3 at low temperatures

The influence of varying the V2O5 content (3–6wt.%) was studied for the selective catalytic reduction (SCR) of nitrogen oxides by ammonia on heteropoly acid (HPA)- and tungsten oxide (WO3)-promoted V2O5/TiO2 catalysts. The SCR activity and alkali deactivation resistance of HPA-promoted V2O5/TiO2 catalysts was found to be much higher than for WO3- promoted catalysts. By increasing the vanadium content from 3 to 5wt.% the catalysts displayed a two fold increase in activity at 225°C and retained their initial activity after alkali doping at a molar K/V ratio of 0.181. Furthermore, the catalysts were characterized by N2 physisorption, XRPD, NH3-TPD, H2-TPR, Raman, FTIR and EPR spectroscopy to investigate the properties of the catalysts. XRPD, Raman and FTIR showed that promotion with 15wt.% HPA does not cause V2O5 to be present in crystalline form, also at a loading of 5wt.% V2O5. Hence, use of HPAs does not cause increased N2O formation or unselective oxidation of NH3. NH3-TPD showed that promotion by HPA instead of WO3 causes the catalysts to possess a higher number of acid sites, both in fresh and alkali poisoned form, which might explain their higher potassium tolerance. Ex-situ EPR spectroscopy revealed that HPA-promoted catalysts have higher V4+/Vtotal ratios than their WO3-promoted counterparts. H2-TPR suggests that HPAs do not have a beneficial effect on the V5+-V3+ redox system, relative to WO3.

ChemInform Abstract: Heteropolyacid‐Based Materials as Heterogeneous Photocatalysts

AbstractReview: &lt;100 refs.

Heteropolyacid‐Based Materials as Heterogeneous Photocatalysts

AbstractInvited for the cover of this issue is the group of Giuseppe Marcì and Leonardo Palmisano at the Università degli Studi di Palermo, Italy. The cover image shows one aspect of the photocatalytic use of heteropolyacids: dye bleaching by irradiation with sunlight.

Thermal decomposition of lignocellulosic biomass in the presence of acid catalysts

Transformation of lignocellulosic biomass to biofuels involves multiple processes, in which thermal decomposition, hydrotreatment are the most central steps. Current work focuses on the impact of several solid acids and Keggin-type heteropolyacids on the decomposition temperature (Td) of pine wood and the characterization of the resulted products. It has been observed that a mechanical mixture of solid acids with pine wood has no influence on Td, while the use of heteropolyacids lower the Td by 100°C. Moreover, the treatment of biomass with a catalytic amount of H3PW12O40 leads to formation of three fractions: solid, liquid and gas, which have been investigated by elemental analysis, TGA, FTIR, GC-MS and NMR. The use of heteropolyacid leads, at 300°C, to a selective transformation of more than 50 wt.% of the holocellulose part of the lignocellulosic biomass. Moreover, 60 wt.% of the catalyst H3PW12O40 are recovered.

ChemInform Abstract: Development and Application of New Oxidation Systems Utilizing Oxometalate Catalysts

AbstractReview: 228 refs.

Heteropolyacids as an efficient and reusable catalytic system for the regiospecific nitration of phenols with metal nitrates

Highly regiospecific mononitration of phenols and substituted phenols is accomplished employing a metal nitrate and a catalytic amount of heteropolyacid in acetonitrile. An exclusive ortho-selectivity was observed with excellent yields. A variety of metal nitrates were used to obtain o-nitrophenols exclusively in good to excellent yields. The use of heteropolyacid is key for the selectivity observed. KEY WORDS : Heteropolyacids, Phenol, Nitration, Regiospecific Bull. Chem. Soc. Ethiop. 2012 , 26(1), 145-152. DOI: http://dx.doi.org/10.4314/bcse.v26i1.17

Development and Application of New Oxidation Systems Utilizing Oxometalate Catalysts

This review describes our recent efforts in the development and application of new oxidation systems utilizing oxometalate catalysts. The novel use of heteropoly acid (HPA), an acidic oxometalate catalyst, in hypervalent iodine-mediated oxidations provided an effective strategy to generate cation radical species that enables a variety of direct C-H functionalizations of aromatic compounds. This strategy brought a facile biaryl synthesis and new spirodienone syntheses in aromatic oxidation chemistry. Moreover, this strategy opens up a facile synthetic route to morphinandienone alkaloids. On the other hand, the use of oxometalate catalyst together with poly(N-isopropylacrylamide) (PNIPAAm)-based polymer in the development of new solid-phase catalyst provided a novel reaction system in water. Due to the characteristic temperature-responsive intelligence of PNIPAAm, this reaction system brought a remarkable acceleration of the reactivity and ease of catalyst recovering in catalytic oxidation that uses hydrogen peroxide or oxygen gas (O<inf>2</inf>) as primary oxidant. In addition, the recovered solid-phase catalyst could be used for consecutive reactions without any significant loss of its catalytic efficacy.

ChemInform Abstract: New and General Nitrogen Heterocycle Synthesis: Use of Heteropoly Acids as a Heterogeneous Recyclable Catalyst.

AbstractFive‐ (pyrrole, tetrahydroindole) and six‐membered (pyridine, tetrahydroquinoline) hetrocycles are accessible via Keggin‐type heteropoly‐acid‐catalyzed condensation of β‐dicarbonyl compounds with β‐ or γ‐amino alcohols.

New and General Nitrogen Heterocycle Synthesis: Use of Heteropoly Acids as a Heterogeneous Recyclable Catalyst

An efficient synthetic method of six- and five-member nitrogen heterocyclic compounds was developed. Nitrogen heterocyclic compounds were prepared by condensation of the β-dicarbonyl compounds with the corresponding β- or γ-amino alcohols, subsequent cyclization, and spontaneous aromatization in the presence of a catalytic amount of Keggin-type heteropoly acids under very mild conditions.

ChemInform Abstract: Recent Developments in Use of Heteropolyacids, Their Salts and Polyoxometalates in Organic Synthesis

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Direct dimethyl-ether proton exchange membrane fuel cells and the use of heteropolyacids in the anode catalyst layer for enhanced dimethyl ether oxidation

In this study, polarization and impedance experiments were performed on a direct dimethyl ether fuel cell (DMEFC). The experimental setup allowed for independent control of water and DME flow rates. The DME flow rate, backpressure, and water flow rate were optimized. Three heteropolyacids, phosphomolybdic acid, H 3PMo 12O 40. (HPMo), phosphotungstic acid, H 3PW 12O 40, (HPW), and silicotungstic acid, H 4SiW 12O 40, (HSiW) were incorporated into the anode catalyst layer in combination with Pt/C. Both HPW-Pt and HSiW-Pt showed higher overall performance than the Pt control. Anodic polarizations were also performed, at 30 psig, Tafel slopes of 67 mV dec −1, 72 mV dec −1, and 79 mV dec −1 were found for HPW-Pt, HSiW-Pt and the Pt control, respectively. At 0 psig, the Tafel slopes were 56 mV dec −1, 58 mV dec −1, and 65 mV dec −1 for HPW-Pt, HSiW-Pt and the Pt control. The trends in the Tafel slope values are in agreement with the polarization data and the electrochemical impedance spectroscopy results. The addition of phosphotungstic acid more than doubled the power density of the fuel cell, compared to the Pt control. When the maximum power density obtained using the HPW-Pt MEA is normalized by the mass of Pt used, the optimal result, 78 mW mg −1 Pt, the highest observed at 30 psig and 100 °C to date.

Recent developments in use of heteropolyacids, their salts and polyoxometalates in organic synthesis

Heteropolyacids, their salts and polyoxometalates have been used as catalysts in wide range of organic reactions such as multi components, oxidation, reductions, electrochemical and photochemical reactions. There have been tremendous and continued efforts to modify the catalytic performance of heteropoly acids such as supporting them on MCM, silica gel, etc. In this review, we have attempted to bring some of new applications of heteropolyacids in organic reactions and recent approaches on modifying them, into focus.

Novel catalytic synthesis of 6,7-dimethoxyisatin with the use of heteropolyacids (HPAs) as acid solid catalyst

Novel catalytic synthesis of 6,7-dimethoxyisatin with the use of heteropolyacids (HPAs) as acid solid catalyst An efficient method for the preparation of 6,7-dimethoxyisatin and its derivatives was developed with good yield by using Preyssler-type heteropolyacid (HPA) as acid catalyst under green conditions. The comparison between Keggin type heteropolyacids, H3[PW12O40], H4[SiW12O40] and H4[SiMo12O40], H3[PMo12O40] and mineral acids with Preyssler's anion shows that the latter possess better catalytical activity than the other heteropolyacids and no degradation of the structure was observed.

Acid catalysis of different supported heteropoly acids for a one-pot synthesis of β-acetamido ketones

The production of β-acetamido ketones from aldehydes, ketones and acetyl chloride in acetonitrile over supported heteropoly acids has been examined. This study reports the use of heteropoly acids (HPAs) supported on metal oxides (SiO 2, Al 2O 3, K 10 and KSF montmorillonite) and activated carbon as efficient and reusable catalysts, and their comparison with other catalysts in Dakin–West reaction. Dodecatungstophosphoric acid supported on KSF and γ-Al 2O 3 shows the best results and reusability.

The Use of Heteropoly Acids as Supports for Low, Ultra-Stable Pt Electrocatalysts.

not Available.

The Use of Heteropoly Acids as Supports for Low, Ultra-Stable Pt Electrocatalysts

We have successfully immobilized several HPA on carbons using covalent attachment. The morphology of these materials is still under investigation, but the hybrid HPA carbons can be used to stabilize nano-Pt particles. The fuel cell performance is not improved over a suitable control electrode. If the correct HPA is used it appears that significant advantages can be obtained in fuel cell catalyst layer stability. Stability over 4000 cycles has been achieved. Encouragingly the F- emission rates from the MEA can be dramatically reduced.