Methanol dehydrogenation on Rh(1 1 1): A density functional and microkinetic modeling study

Abstract

Rh(1 1 1)-catalyzed methanol dehydrogenation is systematically studied based on density functional (DF) calculations and microkinetic modelings. We find that, compared to those for the same reaction on other transition metal surfaces, e.g., Ni(1 1 1), Pd(1 1 1) and Pt(1 1 1), the adsorption configurations of some relevant intermediates on Rh(1 1 1) are relatively abundant and the adsorption potential energy surfaces (PES) are relatively flat. Transition states for all the possible elementary steps involved are searched. Based on the DF results, we model the reaction at two sets of typical reaction conditions, i.e., the low temperatures in ultrahigh vacuum conditions and the high temperature and high pressure conditions. The DF calculations and microkinetic modelings reveal that paths CH 3OH → CH 3O → CH 2O → CHO → CO and CH 3OH → CH 2OH → CHOH → CHO → CO are dominant under all the reaction conditions, whereas at the high temperatures and high pressures, paths CH 3OH → CH 2OH → CH 2O → CHO → CO and CH 3OH → CH 2OH → CHOH → COH → CO are also significant. Under all the considered reaction conditions, apparent activation energy for the methanol decomposition is found to decrease with temperature, and the reaction order of methanol is decreased when increasing its partial pressure. In addition, it is found that it is the very activated adsorption state ( η 1(C)− η 1(O)− η 1(H)) for formaldehyde on Rh(1 1 1) that results in the fact that methanol oxidation does not take place at formaldehyde.