Vapour-phase selective O-methylation of catechol with methanol over Ti-containing aluminium phosphate catalysts

Vapour-phase O-methylation of catechol with methanol has been investigated over Ti-containing aluminium phosphate catalysts (denoted as Al0.77TixP, where x is between 0 and 1.15) prepared by non-uniform precipitation method. The catalytic activities increase with the increase of Ti/P ratio in the range 0-0.23, while further increase of Ti content leads to the decrease of activities. Meanwhile, the selectivity to guaiacol decreased gradually with the increase of Ti/P ratio. The results of various means of characterization demonstrate that the addition of titanium considerably affects the structure of the catalysts, as well as the strength and amount of the acidic and basic sites. The presence of stronger Lewis acidic and/or basic sites in the higher Ti content catalysts should be responsible for the formation of side products (C-alkylation products) and coke, thus quickening the deactivation process of the catalysts. On the other hand, the weak acidic-basic characteristics of the lower Ti content catalysts result in the high selectivity to mono-O-methylation product (guaiacol), and the excellent durability of the catalysts.