Combination of supported bimetallic rhodium–molybdenum catalyst and cerium oxide for hydrogenation of amide

Hydrogenation of cyclohexanecarboxamide to aminomethylcyclohexane was conducted with silica-supported bimetallic catalysts composed of noble metal and group 6–7 elements. The combination of rhodium and molybdenum with molar ratio of 1:1 showed the highest activity. The effect of addition of various metal oxides was investigated on the catalysis of Rh–MoO(x)/SiO(2), and the addition of CeO(2) much increased the activity and selectivity. Higher hydrogen pressure and higher reaction temperature in the tested range of 2–8 MPa and 393–433 K, respectively, were favorable in view of both activity and selectivity. The highest yield of aminomethylcyclohexane obtained over Rh–MoO(x)/SiO(2) + CeO(2) was 63%. The effect of CeO(2) addition was highest when CeO(2) was not calcined, and CeO(2) calcined at >773 K showed a smaller effect. The use of CeO(2) as a support rather decreased the activity in comparison with Rh–MoO(x)/SiO(2). The weakly-basic nature of CeO(2) additive can affect the surface structure of Rh–MoO(x)/SiO(2), i.e. reducing the ratio of Mo–OH/Mo–O(−) sites.