Promoting ethylene epoxidation on gold nanoclusters: self and CO induced O2 activation.

We have investigated the epoxidation of ethylene heterogeneously catalyzed by small gold nanoclusters based on density functional theory calculations. A promising trimolecular Langmuir-Hinshelwood mechanism via co-adsorbed ethylene- and CO-assisted reaction is addressed which provides significant insights into the fundamental catalytic mechanism for ethylene oxidation on small Au nanoclusters. O2 activation is found to be a key step for accelerating ethylene oxidation. Especially, the coadsorbed neighboring CO is found to be more robust for promoting the activation of the O-O bond, resulting in the formation of epoxide and CO2 due to the barrierless process. The new CO-promoted oxidation mechanism has also been clarified by the ab initio MD simulations.