Propylene oxide (PO) is a key precursor of great value to the chemical industry. However, current industrial production methods of PO are either environmentally unfriendly, or not very efficient. In a recent study1, size-selected Ag3 clusters and ~3.5-nanometer Ag aggregates on alumina support were found to be active toward direct propylene epoxidation to PO by molecular oxygen at low temperatures, with negligible amount of carbon dioxide formation. In this work, we have carried out density functional calculations to study the reaction pathways of propylene epoxidation on Ag19, Ag20, and Ag377  including the formation of oxametallocycle, which was shown to be the rate-limiting step previously,1 and the dissociation of of O2 , which was found to play a key role. We also present experimental studies of the UNCD-supported Ag clusters. These are found to be not active toward propylene oxidation, in contrast with the alumina supported Ag clusters. This is probably because that the metal-oxide interfacial sites on the Ag-alumina catalyst that reduces O2 dissociation barrier are absent on the Ag-UNCD catalyst. This limits the O2 dissociation rate and the catalytic activity. 1.  Increased Silver Activity for Direct Propylene Epoxidation via Subnanometer Size Effects, Y. Lei, F. Mehmood, S. Lee, J. Greeley, B. Lee, S. Seifert, R. E. Winans, J. W. Elam, R. J. Meyer, P. C. Redfern, D. Teschner, R. Schl�gl, M. J. Pellin, L. A. Curtiss, and S. Vajda. Science 9 April 2010: 328 (5975), 224-228.

Catalytic activities of Ag aggregates toward direct propylene epoxidation

243rd National Meeting (2012)

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