A molecular insight into propylene epoxidation on Cu/SiO2 catalysts using O2 as oxidant

We investigated the catalytic performances of Cu/SiO2 with various promoters on the epoxidation of C3H6 by O-2. Propylene oxide (PO) is the only product at reaction temperatures below 500 K and the rate of PO formation can reach 2.5 mmol g(-1) h(-1) over the potassium acetate (KAc)-Cu/SiO2 Catalyst. IR studies show that both Cu-0 and Cu+ in Cu/SiO2 can activate the C=C bond Of C3H6, and pi donation of C3H6 to Cu-0 or Cu+ also results in a red shift of v(CO) with respect to CO adsorbed on Cu-0 or Cu+ "solo". However, C3H6 is only weakly adsorbed on Cu2+. Both Cu-0 and Cu+ species show C3H6 epoxidation activity. It is proposed that the isolated Cu species and small CuOx clusters with low valence state (Cu-0 or Cu+) modified by KAc are the main active sites for C3H6 epoxidation on Cu/SiO2 catalyst with O-2 as the oxidant. (C) 2009 Elsevier Inc. All rights reserved.