Effects of support and modifiers on catalytic performance of zinc oxide for hydrogenation of methyl benzoate to benzaldehyde

The ZnO supported on γ-Al2O3, SiO2, MCM-41, and β-zeolite were prepared and examined in the hydrogenation of methyl benzoate (MB). ZnO supported on γ-Al2O3 had a higher activity than ZnO. ZnO/γ-Al2O3 modified with 23 ppm lithium had a high catalytic activity (97%) and high selectivity to benzaldehyde (BD, 87%) in a fixed-bed reactor at atmospheric pressure and 400 °C. Chromium oxide modified ZnO/γ-Al2O3 also had a high selectivity to BD. Hydrogenolysis of MB occurred over copper modified catalysts. X-ray powder diffraction (XRD) revealed that in the ZnO/γ-Al2O3 catalysts, the ZnO, ZnAl2O4 and γ-Al2O3 phases exited mainly, the border of ZnO and ZnAl2O4 might be important for the hydrogenation of MB to BD. XPS and FT-IR revealed that the chemical environment of ZnO on the ZnO/γ-Al2O3 catalyst is different to ZnO and other supported ZnO catalysts, which gives the ZnO/γ-Al2O3 catalyst having a higher activity than ZnO or ZnO on SiO2, MCM-41 or β-zeolite. The presence of third metal (Li, Cr or Cu) oxide in ZnO/γ-Al2O3 could change the electronic structure of Zn and the chemical phenomena of Zn–Al in catalyst and lead to change of the catalytic performance.