Improvement of the selectivity to aniline in benzene amination over Cu/TS-1 by potassium

Abstract

Two different methods of introducing potassium into Cu/TS-1 were conducted and the catalysts obtained showed a rather different catalytic activity in the ammoxidation of benzene to aniline. K could enter the Cu/TS-1 catalyst under reaction conditions, and the resultant catalyst exhibited acceptable selectivity of 99.5% to aniline. However, the catalyst with potassium introduced by wet impregnation exhibited undesirable selectivity (<40%). X-ray photoelectron spectroscopy showed that Ti–O–K formed when potassium was introduced by wet impregnation while K–O–Si formed when K was introduced under reaction conditions. In the latter case, K showed no influence on the Ti site of TS-1, and the formation of K–O–Si species weakened the Brönsted acidity and enhanced the Lewis acid strength, providing active centers for easy adsorption of ammonia, which was considered to be one of the reasons for the high selectivity.