Dehydrogenation of cyclohexanol on Cu–ZnO/SiO2 catalysts: The role of copper species

For the dehydrogenation of cyclohexanol a series of Cu–ZnO/SiO2 catalysts with various Cu to ZnO molar ratios was prepared using the impregnation method, with the loading of copper fixed at 9.5 at.%. The catalysts were characterized by XPS, H2–N2O titration, BET, H2-TPR, NH3-TPD and XRD techniques. The results indicate that the addition of ZnO can improve the dispersion of copper species on reduced Cu–ZnO/SiO2 (CZS) catalysts. Cu0 and Cu+ species were found on the reduced CZS catalysts surface, and the amount of Cu+ increased with the content of ZnO increasing. The addition of ZnO increased the acidity of the CZS catalysts. However, only Cu0 species can be found on the reduced Cu/SiO2 (CS) catalyst surface. According to the reaction results, we found that the selectivity to phenol was related to the amount of Cu+ species, the Cu+ species should be the active sites for the production of phenol, the Cu0 is responsible for cyclohexanol dehydrogenation to cyclohexanone.