氧化铝载体对Pt-Sn/Al2O3催化剂上苯胺和苯甲醇一步合成N-苯基苄胺催化反应性能的影响

以基于借氢策略的苯甲醇和苯胺一步合成N-苯基苄胺为模型反应,研究了三种不同表面结构的氧化铝对其负载的Pt-Sn催化剂上N-烷基化合成仲胺反应性能的影响.采用N₂吸附-脱附法、压汞法、X射线衍射、透射电镜、扫描电镜、CO脉冲吸附、H₂-程序升温还原及NH₃-程序升温脱附等技术对载体和Pt-Sn/Al₂O₃催化剂进行了表征.结果表明,与Al₂O₃相互作用较弱且高度分散的Pt颗粒具有很高的催化活性,Al₂O₃载体较大的孔体积和大孔分布的孔结构有助于反应物扩散和吸附到催化剂表面并提高反应活性.同时也有利于反应产物从催化剂表面离开,从而提高催化剂的稳定性.然而Al₂O₃较强的酸性及酸性分布降低了产物仲胺的选择性和催化剂稳定性.

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

The effect of alumina on the catalytic performance of Pt-Sn/Al₂O₃ 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 N₂ adsorption-desorption, mercury intrusion porosimetry, X-ray diffraction, transmission electron and scanning electron microscopies, CO chemisorption, H₂ temperature-programmed reduction, and NH₃ 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.