The importance of ethyl levulinate (EL) as a fuel additive and a potential biomassderived platform molecule is noteworthy. EL is obtained from the esterification of levulinic acid (LA) in presence of ethanol. Besides LA, the acid-catalyzed ethanolysis reaction to produce EL is carried out on a variety of biomass-derived substrates which include; furfuryl alcohol (FAL), chloromethyl furfural, monosaccharides, polysaccharides and lignocellulosic biomass. The acid catalysts employed for such conversions covers a wide range of structure and properties. The nature of acid catalysts and the key intermediates formed during the reaction dictates the overall yield of the desired product. For example, in the ethanolysis reaction of FAL to produce EL, diethyl ether (DEE) and ethoxymethylfuran (EMF) produced as side products are suggested to influence the selectivity of EL. Similarly, in the ethanolysis of glucose, formation of ethyl-Dglucopyranoside (EDGP) resulted into a slow conversion to produce EL. The review, therefore; is focused on highlighting the importance of catalyst structure, acidity, reaction mechanism and the role of key intermediates in the production of EL from biorenewable resources.EL could either be synthesized directly from biomass or via the transformation of LA, or FAL 20 or chloromethyl furfural (CMF) 23 . All of the suggested reaction routes essentially contain an ethanolysis step in the presence of an acid catalyst. In general, an understanding of the mechanistic routes of product formation, dictates the development of a suitable process for achieving higher yield 24,25 . This could be further strengthened by the design of a suitable homogeneous acid, solid acid or ionic liquid based acid catalysts. On catalytic processing, EL could be converted into an array of higher value chemicals. This review comprehensively covers all the suggested ways of EL production and applications detailing key mechanistic insights, catalytic properties and reaction conditions. Importance of EL as a Fuel AdditiveAlkyl levulinates have shown considerable promises for blending in gasoline and diesel engines, owing to their reduced sulfur content, high lubricity, improved flow properties and flash point stability 20 . The candidate LA esters for this application are methyl, ethyl 26 and butyl levulinates, 23 measuring anti-knocking index of value 106.5, 107.5 and 102.5 respectively 27 . Out of three levulinates, methyl levulinate (ML) is miscible with water and is difficult to separate. With gasoline, ML is lesser miscible and under cold flow conditions is not suitable to blend.Compared to butyl levulinate (BL), EL shows better solubility with diesel range fuels containing higher aromatics 14 . Moreover, NOx emissions were lowered by about 4% on EL blend in diesel as compared to the BL blend. Higher NOx emissions could be attributed to the dilution of lube oil and deposits in combustion chamber, which was observed to be a major problem with BL blended fuels. Furthermore, when propanol or higher alcohols are used for the...
Density functional theory (DFT) calculations were performed to study the mechanism of carbon dioxide (CO 2 ) reduction to carbon monoxide (CO) and methanol (CH 3 OH) on CeO 2 (110) surface. CO 2 dissociates to CO on interacting with the oxygen vacancy on reduced ceria surface.The oxygen atom heals the vacancy site and regenerates the stoichiometric surface via a redox mechanism with intrinsic activation and reaction energies of 259.2 kJ/mole and 238.6 kJ/mole respectively. Lateral interaction of oxygen vacancies were studied by the generation of two oxygen vacancies per unit of CeO 2 surface. Compared to a single isolated vacancy, the activation and reaction energies of CO 2 dissociation on a di-vacancy were approximately reduced to half of its value. Hydrogen atom co-adsorbed on the surface was observed to assist CO 2 dissociation by forming a carboxyl intermediate, CO 2 +H→COOH (∆E act = 39.0 kJ/mole, ∆H = -69.2 kJ/mole) which on subsequent dissociation produces CO via the redox mechanism. On hydrogenation, CO is likely to produce methanol. The energetics of CO hydrogenation to produce methanol showed exothermic steps with activation barriers comparable to the DFT calculations reported for Cu (111) and CeO 2-x /Cu(111) interface. While on the stoichiometric surface, COOH dissociation COOH→CO+OH (∆E act = 55.6 kJ/mole, ∆H =5.7 kJ/mole) is likely to be difficult as compared to rest of the elementary steps, whereas on the reduced surface the energetics of the same step were significantly lowered (∆E act = 47.4 kJ/mole, ∆H = -80.4 kJ/mole). In comparison, hydrogenation of methoxy, H 3 CO+H→H 3 COH, appears to be relatively difficult (∆E act = 58.7 kJ/mole) on the reduced surface.
Dense La0.8Sr0.2MnO3 (LSM) film electrodes with an average thickness of 600 nm were fabricated on yttria-stabilized zirconia and cerium gadolinium oxide by ultrasonic spray pyrolysis. LSM was studied for initial nonstationary behavior by activating with current density for short duration (5 min) and long duration (16 h). The polarization resistance at zero dc bias was reduced upon activation irrespective of the electrolyte, with the reduction more significant after long-duration activation. Short-duration activation was removed by deliberate introduction of La2Zr2normalO7 impurities into the LSM phase or by surface doping with La0.6Sr0.4FeO3 nanoparticles. However, long-duration activation still occurred in these samples. Scanning electron micrographs of short-duration-activated films showed no changes in morphology while long-duration activation resulted in a significant bulk pore formation in the LSM phase. Two distinct mechanisms for LSM activation in a solid oxide fuel cell (SOFC) are proposed. Short-duration activation results in changes in the film surface chemistry while long-duration activation leads to the reconstruction of the LSM phase.
The advent of machine learning (ML) techniques in solving problems related to materials science and chemical engineering is driving expectations to give faster predictions of material properties.
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