Theoretical Studies on the Catalytic Activity of Ag Surface for the Oxidation of Olefins

Systematic theoretical studies for the mechanisms of the epoxidation and complete oxidation of ethylene and propylene over silver surface as well as the reactivity and the stability of oxygen species on Cu, Ag, and Au surfaces have been presented. The Ž . Ž . dipped adcluster model DAM combined with the ab initio Hartree]Fock HF , secondŽ . Ž order Møller-Plesset MP2 , and SACrSAC-CI symmetry-adapted clusterrconfiguration . interaction methods are used. These studies clarify the origin of silver as a unique effective catalyst for the epoxidation of ethylene and the different mechanisms for the oxidation of olefins over silver surface. For the epoxidation of ethylene, the superoxide Oy, which is molecularly adsorbed in bent end-on geometry on the silver surface, is the 2 active species. The origin of the unique catalytic activity of silver for the epoxidation of ethylene is due to its ability to adsorb oxygen as the superoxide species. Such an adsorbed species cannot be stable or exist on Cu and Au surfaces. For the oxidation of propylene, both reaction mechanisms initiated by the activation of olefinic carbon and by the activation of the allyl hydrogen exist. The activation of the allyl hydrogen is the origin of the complete oxidation of some olefins over silver surface. The present results not only let us have a better understanding of the reaction mechanisms of olefins over silver surface but also supply a basic idea for the new catalyst design of the epoxidation reaction. Q 1997 John Wiley & Sons, Inc. Int J Quant Chem 65: 839]855, 1997 U Present address: Department of Chemistry, School of Science and Engineering, Waseda University, Ohkubo 3-4-1, Shinjukuku, Tokyo 169, Japan. Correspondence to: H. Nakatsuji. Contract grant sponsor: Japanese Ministry of Education, Science, and Culture and the New Energy and Industrial TechŽ . nology Development Organization NEDO . ( ) International Journal of Quantum Chemistry, Vol. 65, 839]855 1997 Q 1997 John Wiley & Sons, Inc. CCC 0020-7608 / 97 / 050839-17 NAKATSUJI, HU, AND NAKAI