Effect of nickel promoter in Au/TS-1 catalysts for gas-phase propylene epoxidation

Au active sites on titanium silicalite are essential for the propylene epoxidation with H2 and O2. To improve the amount of Au active sites Ni(II) as promoter was used to change the surface charge state of TS-1 support so that more Au species can be attracted to deposit on TS-1 (Au–Ni(II)/TS-1). The dispersion and the valence state of the Au and Ni species on Au-Ni(II)/TS-1 were analyzed by HAADF-STEM and XPS, respectively. Both the Au capture efficiency and the Au loading increased greatly with Ni(II) content but overmuch Au loading (0.396%) can result in the rapid agglomeration of the Au nanoparticles on the outer surface of TS-1 and lead to poor catalytic performance. So through regulating both the concentrations of Ni and Au species, the best comprehensive performance was reached on the catalyst 0.212Au0.154Ni(II)/TS-1 (0.212 wt% of Au and 0.154 wt% of Ni(II)) at 170 °C, propylene oxide (PO) formation rate of 154 gPOh−1 kgcat−1, and H2 efficiency of 31%. The results could guide us to maximize the utilization efficiency of Au precursor and H2 more reasonably.