From stable structures of vertical crotonaldehyde (CAL) adsorption on alloy surfaces of M/Au (111) (M=In

Ir)

reaction mechanisms of incomplete hydrogenation (C＝O addition

C＝C addition

and 1

4-conjugate addition) of CAL on the M/Au (111) surface were studied by density functional theory (DFT) in combination with periodic slab model. Calculation of activation energy and heat of elementary step reactions and analysis of conformation change at various hydrogenation mechanisms showed that CAL on the In/Au (111) and Ir/Au (111) planes first hydrogenated near-surface C＝O by A2 mechanism

which an H atom was first added to active C on generation of MS1 and then another H atom was added to intermediate MS1. Both elementary reactions were exothermic but the first one was the rate-determining step due to higher activation energy. The maximum energy barrier of elementary reactions of CAL hydrogenation by the optimal hydrogenation mechanism on In/Au (111) surface was 0.969 eV

which was much lower than that of 1.332 eV on the Ir/Au (111) surface. Hence

In/Au (111) had better catalytic activity than Ir/Au (111) surface for incomplete hydrogenation of CAL. Adsorption of reactant and products on M/Au (111) surface indicated that formation of strong chemical adsorption between crotonaldehyde O atom and alloy doping element M improved selectivity of M/Au (111) to C＝O hydrogenation.