The essence of Na+ and Zn species in propylene epoxidation by oxygen on Na2CO3 modified Cu-Zn/SiO2 catalysts

Abstract

The catalytic performances of Cu-Zn/SiO2 with different Zn content and promoter on C3H6 epoxidation were investigated. Zn species was in favour of the formation of propylene oxide (PO), and PO selectivity was further increased after Cu-Zn/SiO2 was modified by Na+. The promotive effect of Na+ on C3H6 epoxidation activity was much superior to that of Cl−. The PO formation rate on Cu92Zn8/SiO2-Na2CO3 was nearly as high as 50 times that on Cu/SiO2. Zn and Na+ could synergistically promote the reduction of Cu2+ to Cu+ species. The variation tendencies between C3H6 epoxidation activity and Cu+ content were in good agreement with each other. The role of Zn and Na+ was to enhance the Cu+ content via promoting the reduction of Cu2+ to Cu+ induced by Zn and Na+. Cu+ species played a vital role in PO formation and Cu+ may be the active site for C3H6 epoxidation reaction by O2.