Vapor phase ortho-selective alkylation of phenol with methanol over silica-manganese mixed oxide catalysts

摘要

The gas phase catalytic alkylation of phenol with methanol was investigated over a series of silica-manganese mixed oxide catalysts. The molar ratio of Si/Mn, the calcination temperature and the reaction temperature have considerable effect on the catalytic performance of the catalysts. All the Si-Mn mixed oxides are the active catalysts for the selective production of o-cresol and 2,6-xylenol. Among them, the catalyst with Si/Mn=0.02, which is calcined at 773 K, shows the highest catalytic activity and selectivity to 2,6-xylenol. The existence of suitable Lewis acidic sites and/or basic sites might be responsible for the high activity and the ortho-selectivity of Si-Mn mixed oxides. During the reaction course, the partial reduction of Mn2O3/Mn3O4 can result in the decrease of Lewis acidity strength, which might be the main reason for the decrease of the selectivity to 2,6-xylenol.