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 O2. 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 Cu0 and Cu+ in Cu/SiO2 can activate the Cdouble bond; length as m-dashC bond of C3H6, and π donation of C3H6 to Cu0 or Cu+ also results in a red shift of νCO with respect to CO adsorbed on Cu0 or Cu+ “solo”. However, C3H6 is only weakly adsorbed on Cu2+. Both Cu0 and Cu+ species show C3H6 epoxidation activity. It is proposed that the isolated Cu species and small CuOx clusters with low valence state (Cu0 or Cu+) modified by KAc are the main active sites for C3H6 epoxidation on Cu/SiO2 catalyst with O2 as the oxidant.