Hydrogenation Of Phenol Over Carbon Nanotubes-supported Noble Metal Catalysts

In this paper,carbon nanotubes?CNTs?were modified with different ways,and the catalysts of Pt/CNTs and Pd/CNTs were prepared by loading Pt and Pd on the modified CNTs.The catalytic performance of th catalysts were tested using the phenol hydrogenation reaction as a probe.The effects of preparation conditions of the Pt/CNTs and Pd/CNTs and reaction conditions of the phenol hydrogenation on the catalytic performance of the catalysts were studied.The study about the surface modification of CNTs showed that the catalytic effect of modified Pt/CNTs catalyst by mixing concentrated nitric acid and hydrogen peroxide was the best.The reaction was carried out with the pressure of 0.5 MPa H₂ and the temperature of 50 °C for 30 min,the reaction rate of Pt/CNTs on phenol hydrogenation was 0.650 molphenol/?molPt·s?,the selectivity of cyclohexanone was 75.6%.Under the same conditions,the catalyst modified by concentrated nitric acid was used for the phenol hydrogenation reaction,the cyclohexanone selectivity was 75.3%,but the reaction rate was only 0.324 molphenol/?molPt·s?.The Pt/CNTs catalyst was prepared by H₂ reduction,then it was treated at 300 °C with N₂,the rate of phenol hydrogenation was further increased to 0.959 molphenol/?molPt·s?,but the selectivity of cyclohexanone was reduced to 60.5%.The reduction method of sodium formate in non-H₂ reduction was best,the corresponding phenol hydrogenation conversion rate was 93.6%,the cyclohexanone selectivity was 73.9%,and the reaction rate was 0.898 molphenol/?mol Pt·s?.The loading method of Pt on CNTs show that the catalyst activity can be improved by the inner tube loading method.The reaction was carried out with the pressure of 0.5 MPa H₂ and the temperature of 50 °C for 30 min,the reaction rate of Pt/CNTs on phenol hydrogenation was 0.934 molphenol/?molPt·s?,the selectivity of cyclohexanone was 77.5%.The modified CNTs was treated by mixing concentrated nitric acid and hydrogen peroxide,then it was used to prepare the Pd/CNTs catalyst for phenol hydrogenation reaction.This reaction was carried out with the pressure of 1.0 MPa and the temperature of 80 °C for 60 min,the reaction rate of Pd/CNTs on phenol hydrogenation was 0.041 molphenol/?molPd·s?,the selectivity of cyclohexanone was 99.9%.Under the same conditions,the catalyst modified by concentrated nitric acid was used for the phenol hydrogenation reaction,the cyclohexanone selectivity was 96.2%,but the reaction rate was only 0.025 molphenol/?molPd·s?.The Pd/CNTs catalyst was prepared by H₂ reduction,then it was treated at 300 °C with N₂ for 3 h,the activity of phenol hydrogenation can be further increased.The reduction method of sodium formate in non-H₂ reduction was best.The reaction system of Pt/CNTs and Pd/CNTs on phenol hydrogenation used dichloromethane-water mixed solvent,or introducing the Lewis acid can significantly improve the performance of phenol hydrogenation reaction.Extending the reaction time and improving the reaction temperature and pressure could effectively increase the phenol conversion rate,but the cyclohexanone selectivity was declined.