Mesoporous silicon sulfonic acid as a highly efficient and stable catalyst for the selective hydroamination of cyclohexene with cyclohexylamine to dicyclohexylamine in the vapor phase

Abstract

In this work, a new mesoporous silicon sulfonic acid catalyst derived from silicic acid has been successfully prepared by the chemical bonding method. The physico-chemical properties of mesoporous silicon sulfonic acid catalysts have been systematically characterized using various techniques. The results demonstrate that sulfonic acid groups have been grafted on silicic acid by forming a new chemical bond (Si-O-S). The mesoporous silicon sulfonic acid exhibits excellent catalytic performance and stability in the vapor phase hydroamination reaction of cyclohexene with cyclohexylamine. Cyclohexene conversion of 61% and 97% selectivity to dicyclohexylamine was maintained after running the reaction for over 350 h at 280 °C. The developed mesoporous silicon sulfonic acid catalyst shows advantages of low cost, superior acid site accessibility, and long term reactivity stability. Moreover, a possible catalytic hydroamination reaction mechanism over silicon sulfonic acid was suggested. It has been demonstrated that the sulfonic acid groups of the catalyst play an important role in the hydroamination. The present work provides a simple, efficient, and environmentally friendly method for the hydroamination of cyclohexene to valuable dicyclohexylamine, which also shows important industrial application prospects.