TiO_2-Al_2O_3-AlPO_4复合物在甲苯歧化反应中的催化行为

Disproportionation of Toluene over Ti-Al-P Oxide

用共沉淀法制备了一系列无定形、大孔TiO_2-Al_2O_3-AlPO_4复合氧化物,并用TPD和IR技术表征了它们的酸性。在甲苯歧化反应中,发现这类非择形催化剂对二甲苯选择性大于40％。对于这种现象,根据实验和量子化学计算中的定域能方法所得结果,给予了解释。

A series of amorphous, large hole compounds of TiO_2-Al_2O_3-AlPO_4 were prepared by co-precipitation method. NH_3-TPD and IR confirm that the surface of TiO_2-Al_2O_3-AlPO_4 is characteristic of smaller acidic amount and weak acidity as well as more Lewis acidic sites. The toluene disproportionation over TiO_2-Al_2O_3-AlPO_4 type of catalysts were studied.It was found that toluene disproportionation over this kind of non-shape selective catalysts gave para isomer more than 40％ in the xylene product and the conversion depended on the concentration of acidic sites on the surface. This can be explained in terms of the formation of transition state 4-methyl-diphenylmethane and competition of the isomerization of the methyl group moving around the ring by stepwise with diffusion out of the pores.