Effect of alumina support on catalytic performance of Pt-Sn/Al2O3 catalysts in one-step synthesis of N-phenylbenzylamine from aniline and benzyl alcohol

Abstract

The effect of alumina on the catalytic performance of Pt-Sn/Al 2 O 3 catalysts in the green synthesis of secondary amines by N -alkylation of amines with alcohols based on the borrowing hydrogen strategy was investigated. N -alkylation of aniline with benzyl alcohol to produce N -phenylbenzylamine was used as a model reaction. Three different alumina supports were selected, and the corresponding catalysts were prepared by complex impregnation under vacuum. The supports and catalysts were characterized using N 2 adsorption-desorption, mercury intrusion porosimetry, X-ray diffraction, transmission electron and scanning electron microscopies, CO chemisorption, H 2 temperature-programmed reduction, and NH 3 temperature-programmed desorption. The results show that the catalysts with small Pt particles that were highly dispersed on the alumina supports and interacted weakly with the supports had high catalytic activities. The large pore volumes and pore size distributions of the alumina supports helped diffusion and adsorption of the reactants on the catalyst surface and increased the catalytic activity; they also promoted removal of the products from the catalyst surface and enhanced the catalytic stability. However, strong acidity and acid distribution of the alumina supports decreased the selectivity for secondary amines and reduced the catalyst stability. Pt-Sn/Al 2 O 3 catalysts with highly dispersed Pt particles, weak acid sites, acid distributions, and large pore volumes and pore size distributions have excellent catalytic performance in the synthesis of secondary amines.