The effect of a silica support: a density functional theory study of the C-H bond activation of ethane on a nickel oxide cluster

Abstract

The support effect is an important issue in heterogeneous catalysis. A systematic density functional theory computational study is reported here to better understand the C–H bond activation steps in the reaction between C2H6 and a model silica-supported Ni3O3 cluster, as well as that between C2H6 and an unsupported Ni3O3 cluster. Two mechanisms, namely, a radical mechanism (denoted as mechanism A) and a concerted mechanism (denoted as mechanism B) were examined. Both of these mechanisms contain two steps. For the C–H bond activation taking place via mechanism A, the involvement of the model silica support does not change the most favorable pathway significantly; however, it does result in a modest increase in the reaction barrier and the overall Gibbs energy change. For the C–H bond activation taking place via mechanism B, the involvement of the model silica support leads to an increase in the reaction barrier in the first step. The product of this step has a noticeable difference in the structures for the Ni3O3 moiety in the unsupported and model silica-supported systems. The result of charge analysis shows that there is no noticeable charge transfer between the silica support and Ni3O3 when they are in the starting reactants, while there is an electron withdrawal from Ni3O3 by the silica support when they are in transition states, intermediates, or products. The results here provide deeper insights into the support effect on the C–H bond activation of lower alkanes on supported transition metal catalysts. Copyright © 2015 John Wiley & Sons, Ltd.