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

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.

► Si–Mn mixed oxides exhibit excellent catalytic activity for phenol methylation.
► Si/Mn ratio and calcination temperature influence catalytic performance.
► High yield of 2,6-xylenol can be achieved on the optimized Si–Mn mixed oxides catalyst.
► Relatively strong Lewis acid centers favor the formation of 2,6-xylenol.