Effect of manganese on Cu/SiO2 catalysts for the dehydrogenation of cyclohexanol to cyclohexanone

The effect of the addition of manganese to Cu/SiO2 catalysts for cyclohexanol dehydrogenation reaction was investigated. At reaction temperature of 250 °C, the conversion and the selectivity to cyclohexanone were both increased with the addition of manganese to Cu/SiO2 catalyst. However, as the reaction temperature was further increased, higher loading of manganese in Cu/SiO2 catalyst led to a decrease in the conversion of cyclohexanol. Manganese in Cu/ SiO2 catalyst decreased the reduction temperature of copper oxide, increased the dispersion of copper metal, and decreased the selectivity to cyclohexene. It was found that the dehydration of cyclohexanol to cyclohexene occurred on the intermediate acid sites of catalyst. At high Mn loading, catalyst surface was more enriched with manganese in used catalyst compared to that in freshly calcined or reduced catalyst, which may account for the sharp decrease of the conversion at high temperature of 390 °C. Upon reduction, copper manganate on silica was decomposed into fine particles of copper metal and manganese oxide (Mn3O4).