In situ UV-vis and EPR study on the formation of hydroperoxide species during direct gas phase propylene epoxidation over Au/Ti-SiO2 catalyst

In recent years, there have been great experimental and theoretical advances in the understanding of the epoxidation of propylene by O-2 and H-2 over Au supported on titanium-containing oxidic supports; however, thus far spectroscopic evidence of reacting species for proposed mechanisms has been lacking. Hydroperoxide species have been postulated as an intermediate responsible for the epoxidation of propylene with O-2 and H-2. In order to obtain direct evidence for the different type of active oxygen species, in situ UV-vis and EPR measurements were carried out during the epoxidation of propylene with O-2 and H-2 over a Au/Ti-SiO2 (Ti/Si = 3:100) catalyst. It was determined that the adsorbed species of oxygen (O-2(-)) resided on Au, more likely at a perimeter site, and it led to the formation of titanium hydroperoxo species. These results support the possible mechanism of formation of these hydroperoxo species via H2O2 produced from O-2 and H-2 adsorbed on the Au surfaces.