In a world faced with energy crisis, it is indispensable to shift to alternate sources of energy. Bioethanol, an energy source produced from the fermentation of lignocellulosic biomass can be employed to produce hydrogen gas and methane by steam reforming and hydrogenation respectively. Density Functional Theory and microkinetic modelling1 using CatMap have been utilized to determine the catalytic activity and selectivity trends of these reactions over stepped sites of transition state metals. For bioethanol hydrogenation, various routes for decomposition have been studied: α-H abstraction, β-H abstraction, C-C, C-O, and O-H bond scission. Methane and carbon monoxide have been found to be the major product with ethane and methanol produced at very low rates. The energy barrier for α-H abstraction has been found to be the lowest of all. Ru, Rh, Ir cleave both C-C and C-O bonds, however the rate of methane formation(C-C cleavage) is higher – 10-1/s. Pd and Pt selectively cleave C-C bond as compared to C-O cleavage producing methanol and methane. Steam reforming of ethanol produces hydrogen and carbon dioxide, the catalysts with highest turnover being Ru, Rh, Ir. In the microkinetic model, the energy of all the adsorbed species is scaled with carbon and oxygen binding energy on the metal surface and transition states energy are obtained by transition state scaling relations. Volcano plots for both the schemes have been constructed. The catalytic trend for ethanol decomposition on hydrogenation is – Rh &gt; Ir &gt; Ru &gt; Pd &gt; Pt &gt; Cu &gt; Ag, Au and that for steam reforming is – Rh &gt; Ru, Ir &gt; Ni &gt; Co &gt; Pt, Pd &gt; Fe &gt; Au, Ag as shown in Figure1 and Figure2 respectively. For Pd, Pt and Cu, the turnover frequency is lower as decomposition of ethanol is limited by adsorption of intermediate species. On Ag and Au, the reaction is slow as being a noble metal, it is unable to activate ethanol and other intermediates. Fe binds intermediates too strongly, poisoning the surface, resulting in low throughput of the product in case of steam reforming. 1. Hanne Falsig, Juan Shen, Tuhin Suvra Khan, Wei Guo, Glenn Jones, Søren Dahl, Thomas Bligaard, Topics in Catalysis, 2015, 57, 80-88

Catalytic processing of bioethanol on transition state metals

253rd National Meeting (2017)

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