Understanding of ethanol decomposition on Rh(1 1 1) from density functional theory and kinetic Monte Carlo simulations

Abstract

Reaction mechanisms of ethanol decomposition on Rh(1 1 1) were elucidated by means of periodic density functional theory (DFT) calculations and kinetic Monte Carlo (KMC) simulations. We propose that the most probable reaction pathway is via CH 3CH 2O* on the basis of our mechanistic study: CH 3CH 2OH* → CH 3CH 2O* → CH 2CH 2O* → CH 2CHO* → CH 2CO* → CHCO* → CH* + CO* → C* + CO*. In contrast, the contribution from the pathway via CH 3CHOH* is relatively small, CH 3CH 2OH* → CH 3CHOH* → CH 3CHO* → CH 3CO* → CH 2CO* → CHCO* → CH* + CO* → C* + CO*. According to our calculations, one of the slow steps is the formation of the oxametallacycle CH 2CH 2O* species, which leads to the production of CHCO*, the precursor for C–C bond breaking. Finally, the decomposition of ethanol leads to the production of C and CO. Our calculations, for ethanol combustion on Rh, the major obstacle is not C–C bond cleavage, but the C contamination on Rh(1 1 1). The strong C–Rh interaction may deactivate the Rh catalyst. The formation of Rh alloys with Pt and Pd weakens the C–Rh interaction, easing the removal of C, and, as expected, in accordance with the experimental findings, facilitating ethanol combustion.