Showing papers on "Methanol published in 2009"

Palladium-Based Electrocatalysts for Alcohol Oxidation in Half Cells and in Direct Alcohol Fuel Cells

Abstract: Direct alcohol fuel cells (DAFCs) are attracting increasing interest as power sources for portable applications due to some unquestionable advantages over analogous devices fed with hydrogen.1 Alcohols, such as methanol, ethanol, ethylene glycol, and glycerol, exhibit high volumetric energy density, and their storage and transport are much easier as compared to hydrogen. On the other hand, the oxidation kinetics of any alcohol are much slower and still H2-fueled polymer electrolyte fuel cells (PEMFCs) exhibit superior electrical performance as compared to DAFCs with comparable electroactive surface areas.2,3 Increasing research efforts are therefore being carried out to design and develop more efficient anode electrocatalysts for DAFCs.

Ternary Pt/Rh/SnO2 electrocatalysts for oxidizing ethanol to CO2.

Abstract: The development of a direct ethanol fuel cell has been hampered by ethanol’s inefficient and slow oxidation. A ternary electrocatalyst consisting of platinum and rhodium deposited on carbon-supported tin dioxide nanoparticles is now shown to oxidize ethanol to carbon dioxide with high efficiency by splitting C–C bonds at room temperature. Ethanol, with its high energy density, likely production from renewable sources and ease of storage and transportation, is almost the ideal combustible for fuel cells wherein its chemical energy can be converted directly into electrical energy. However, commercialization of direct ethanol fuel cells has been impeded by ethanol’s slow, inefficient oxidation even at the best electrocatalysts1,2. We synthesized a ternary PtRhSnO2/C electrocatalyst by depositing platinum and rhodium atoms on carbon-supported tin dioxide nanoparticles that is capable of oxidizing ethanol with high efficiency and holds great promise for resolving the impediments to developing practical direct ethanol fuel cells. This electrocatalyst effectively splits the C–C bond in ethanol at room temperature in acid solutions, facilitating its oxidation at low potentials to CO2, which has not been achieved with existing catalysts. Our experiments and density functional theory calculations indicate that the electrocatalyst’s activity is due to the specific property of each of its constituents, induced by their interactions. These findings help explain the high activity of Pt–Ru for methanol oxidation and the lack of it for ethanol oxidation, and point to the way to accomplishing the C–C bond splitting in other catalytic processes.

Conversion of Carbon Dioxide into Methanol with Silanes over N‐Heterocyclic Carbene Catalysts

Abstract: Activate and reduce: Carbon dioxide was reduced with silane using a stable N-heterocyclic carbene organocatalyst to provide methanol under very mild conditions. Dry air can serve as the feedstock, and the organocatalyst is much more efficient than transition-metal catalysts for this reaction. This approach offers a very promising protocol for chemical CO(2) activation and fixation.

Enzymatic transesterification of Jatropha oil

Abstract: Transesterification of Jatropha oil was carried out in t-butanol solvent using immobilized lipase from Enterobacter aerogenes. The presence of t-butanol significantly reduced the negative effects caused by both methanol and glycerol. The effects of various reaction parameters on transesterification of Jatropha oil were studied. The maximum yield of biodiesel was 94% (of which 68% conversion was achieved with respect to methyl oleate) with an oil:methanol molar ratio of 1:4, 50 U of immobilized lipase/g of oil, and a t-butanol:oil volume ratio of 0.8:1 at 55°C after 48 h of reaction time. There was negligible loss in lipase activity even after repeated use for seven cycles. To the best of our knowledge this is the first report on biodiesel synthesis using immobilized E. aerogenes lipase.

A first principles comparison of the mechanism and site requirements for the electrocatalytic oxidation of methanol and formic acid over Pt

Abstract: First principles density functional theoretical calculations were carried out to examine and compare the reaction paths and ensembles for the electrocatalytic oxidation of methanol and formic acid in the presence of solution and applied electrochemical potential. Methanol proceeds via both direct and indirect pathways which are governed by the initial C–H and O–H bond activation, respectively. The primary path requires an ensemble size of between 3–4 Pt atoms, whereas the secondary path is much less structure sensitive, requiring only 1–2 metal atoms. The CO that forms inhibits the surface at potentials below 0.66 V NHE. The addition of Ru results in bifunctional as well as electronic effects that lower the onset potential for CO oxidation. In comparison, formic acid proceeds via direct, indirect and formate pathways. The direct path, which involves the activation of the C–H bond followed by the rapid activation of the O–H bond, was calculated to be the predominant path especially at potentials greater than 0.6 V. The activation of the O–H bond of formic acid has a very low barrier and readily proceeds to form surface formate intermediates as the first step of the indirect formate path. Adsorbed formate, however, was calculated to be very stable, and thus acts as a spectator species. At potentials below 0.6 V NHE, CO, which forms via the non-Faradaic hydrolytic splitting of the C–O bond over stepped or defect sites in the indirect path, can build up and poison the surface. The results indicate that the direct path only requires a single Pt atom whereas the indirect path requires a larger surface ensemble and stepped sites. This suggests that alloys will not have the same influence on formic acid oxidation as they do for methanol oxidation.

Simultaneous transesterification and esterification of unrefined or waste oils over ZnO-La2O3 catalysts

Abstract: A single-step method was developed for biodiesel production from unrefined or waste oils using a series of heterogeneous zinc and lanthanum mixed oxides. Effects of metal oxide molar ratio, free fatty acids (FFA) and water content in feedstock, molar ratio of methanol and oil, and reaction temperature on the yield of biodiesel were investigated. A strong interaction between Zn and La species was observed with enhanced catalyst activities. Lanthanum promoted zinc oxide distribution, and increased the surface acid and base sites. The catalyst with 3:1 ratio of zinc to lanthanum was found to simultaneously catalyze the oil transesterification and fatty acid esterification reactions, while minimizing oil and biodiesel hydrolysis. A reaction temperature window of 170–220 °C was found for the biodiesel formation. A high yield (96%) of fatty acid methyl esters (FAME) was obtained within 3 h even using unrefined or waste oils.

Synthesis of γ-Valerolactone by Hydrogenation of Biomass-derived Levulinic Acid over Ru/C Catalyst

Abstract: Ru/C catalyst was used in hydrogenation of levulinic acid to produce γ-valerolactone. The conversion rate and the selectivity of levulinic acid to γ-valerolactone with Ru/C as catalyst were higher than those with Pd/C, Raney nickel, and Urushibara nickel. The optimum preparation conditions of γ-valerolactone by hydrogenation of levulinic acid catalyzed by Ru/C were as follows: temperature at 130 °C, hydrogen pressure at 1.2 MPa, dosage of catalyst at 5.0% (based on the mass fraction of levulinic acid), the solvent being methanol, and a reaction time of 160 min. The conversion rate of levulinic acid to γ-valerolactone was found to be 92%, and the selectivity of γ-valerolactone was 99%. The surface structure variations of the fresh and used catalysts were characterized by XRD and XPS. Furthermore, the reaction pathway for the hydrogenation of levulinic acid was proposed.

Mechanism of ethanol synthesis from syngas on Rh(111).

Abstract: Rh-based catalysts display unique efficiency and selectivity in catalyzing ethanol synthesis from syngas (2CO + 4H2 → C2H5OH + H2O). Understanding the reaction mechanism at the molecular level is the key to rational design of better catalysts for ethanol synthesis, which is one of major challenges for ethanol application in energy. In this work, extensive calculations based on density functional theory (DFT) were carried out to investigate the complex ethanol synthesis on Rh(111). Our results show that ethanol synthesis on Rh(111) starts with formyl formation from CO hydrogenation, followed by subsequent hydrogenation reactions and CO insertion. Three major products are involved in this process: methane, methanol, and ethanol, where the ethanol productivity is low and Rh(111) is highly selective to methane rather than ethanol or methanol. The rate-limiting step of the overall conversion is the hydrogenation of CO to formyl species, while the selectivity to ethanol is controlled by methane formation and C−...

Oil transesterification over calcium oxides modified with lanthanum

Abstract: Investigations were conducted on a series of calcium and lanthanum oxides catalyst for biodiesel production. Mixed oxides catalyst showed a superior transesterification activity over pure calcium or pure lanthanum oxide catalysts. The catalyst activity was correlated with surface basicity and specific surface areas. The effects of water and free fatty acids (FFA) levels in oil feedstock, water and CO2 in air, mass ratio of catalyst, molar ratio of oil to methanol, and reaction temperature on fatty acid methyl ester (FAME) yield were investigated. Under optimal conditions, FAME yields reached 94.3% within 60 min at 58 °C. Mixed CaO-La2O3 catalyst showed a high tolerance to water and FFA, and could be used for converting pure or diluted unrefined/waste oils to biodiesel.

The Effect of Acid Strength on the Conversion of Methanol to Olefins Over Acidic Microporous Catalysts with the CHA Topology

Abstract: The present work addresses the influence of acid strength on the stability and product selectivity of microporous catalysts with CHA framework type The two studied catalysts, H-SAPO-34 and H-SSZ-13, have the same topology, density of acid sites (approximately one acid site per cage), and crystal size (02–2 microns), but their acid strength differ due to the framework composition The difference in acid strength was determined by infrared spectroscopy, using CO as probe molecule Catalytic tests were performed in a fixed bed flow reactor at 300–425 °C and WHSV = 60 h−1 It was observed that the acid strength has significant influence on reaction rates, enhancing the production rate of olefins in the reactor effluent as well as aromatics retained in the catalyst pores and leading to a lower optimal temperature of operation for the more acidic H-SSZ-13 catalyst The activation and deactivation patterns and the intermediates formed are very similar for the two materials The ethene to propene ratio increases with temperature and time on stream for both catalysts, and is higher over the more acidic H-SSZ-13 catalyst at similar reaction conditions

Heterogeneous catalysis of calcium oxide used for transesterification of soybean oil with refluxing methanol

Abstract: Much interest has been taken in finding a solid base catalyst for a reaction to produce biodiesel. Calcium oxide has the great advantage of the enhanced catalytic activity, but the soluble substance is leached away from the solid base catalyst during the reaction. In this paper, the leaching of solid base catalyst was investigated on the basis of data from the heterogeneous catalytic transesterification of soybean oil at reflux of methanol. When calcium oxide was employed for the reaction, the calcium contents of the produced oil and glycerol were 139 and 4602 ppm, respectively. This data indicated that the amount of the soluble substance corresponded to 10.5 wt% of the employed catalyst. Since calcium oxide was transformed into calcium diglyceroxide at the beginning of the reaction, many of the soluble substances derived from calcium diglyceroxide. Also, the soluble substances were rather active in the soybean oil transesterification. On the other hand, calcium diglyceroxide was employed for the reaction, with the result that the amount of the soluble substance was only 4.0 wt%. In this case, the soluble substance did not catalyze the conversion of soybean oil into its methyl esters. Based on the experimental results, the heterogeneous catalysis of calcium oxide was discussed. Additionally, removal of the soluble substance by cation-exchange resin was tested in order to purify the produced oil.

Immobilized Lipase on Fe3O4 Nanoparticles as Biocatalyst for Biodiesel Production

Abstract: In this work, magnetic Fe3O4 nanoparticles treated with (3-aminopropyl)triethoxysilane were used as immobilization material Lipase was covalently bound to the amino-functionalized magnetic nanoparticles by using glutaraldehyde as a coupling reagent with the activity recovery up to 70% and the enzyme binding efficiency of 84% The binding of lipase to the magnetic particles was confirmed by enzyme assays, transmission electron microscopy, X-ray powder diffraction, and Fourier transform infrared spectra Moreover, the immobilized lipase was found to be able to catalyze the transesterification of soybean oil with methanol to produce fatty acid methyl esters (better known as biodiesel) Besides, it was determined that the conversion of soybean oil to biodiesel fuels reached over 90% by the three-step addition of methanol when 60% immobilized lipase was employed Further study showed that the immobilized lipase could be used four times without significant decrease of activity

Conversion of biomass to fuel: Transesterification of vegetable oil to biodiesel using KF loaded nano-γ-Al2O3 as catalyst

Abstract: KF-impregnated nanoparticles of γ-Al2O3 were calcinated and used as heterogeneous catalysts for the transesterification of vegetable oil with methanol for the synthesis of biodiesel (fatty acid methyl esters, FAME). The ratio of KF to nano-γ-Al2O3, calcination temperature, molar ratio of methanol/oil, transesterification reaction temperature and time, and the concentration of the catalyst were used as the parameters of the study. A methyl ester yield of 97.7 ± 2.14% was obtained under the catalyst preparation and transesterification conditions of KF loading of 15 wt%, calcination temperature of 773 K, 8 h of reaction time at 338 K, and using 3 wt% catalysts and molar ratio of methanol/oil of 15:1. This relatively high conversion of vegetable oil to biodiesel is considered to be associated with the achieved relatively high basicity of the catalyst surface (1.68 mmol/g) and the high surface to volume ratio of the nanoparticles of γ-Al2O3.