Impact of the degree of dehydrogenation in ethanol C-C bond cleavage on Ir(100).

Abstract

A lack of comprehensive studies of the C-C bond cleavage in organic molecules hampers the rational design of catalysts for many applications, such as in fuel cells and steam reforming technologies. Employing ethanol on Ir(100) as an example, we studied 14 C-C bond cleavages of various species involved in the ethanol oxidation reaction using density functional theory calculations and used the degree of dehydrogenation (DoDH) of the reactant species as a variable to correlate the C-C bond cleavage barrier and reaction energy. This correlation method was also applied to the dehydrogenation reactions of ethanol on various catalysts, and great insight was obtained. The results show that the C-C cleavage barrier generally decreases with DoDH, with a local minimum around 33.3% DoDH. For reactants having more than 50% DoDH, the C-C cleavage is more ready to take place than the dehydrogenation and can occur at room temperature. Furthermore, the O atom in the reactive species plays a critical role in lowering the C-C bond cleavage barrier. The results provide necessary inputs for kinetic studies of ethanol reactions under operando conditions, where a reaction network beyond the minimum energy pathway is needed. The results will also serve as a benchmark for future studies of the ethanol C-C cleavage on other facets of Ir catalysts or on different catalysts. Furthermore, this work demonstrates that the proposed method opens up a new and effective way of correlating catalytic activities for the C-C bond cleavage involving long-chain alkanes and alcohols.