Vapour-phase O-methylation of Catechol with Methanol on Ti-containing Phosphate Catalysts

Ti-containing phosphate(Ti-P-O) catalysts with different molar ratios of P to Ti(0-2.0) were synthesized and characterized by XRD, N2-adsorption/desorption, IR and temperature-programmed desorption(TPD) methods. The catalytic properties of Ti-P-O samples in the vapor-phase O-methylation of catechol with methanol were also studied. The catechol conversion increases with the increase of the molar ratio of P to Ti in a range of 0-0.33, while a further increase in the P content leads to a decrease of the catalytic activity. Meanwhile, the selectivities of the catalysts to the main product(guaiacol) increase gradually with the increase of the molar ratio of P to Ti. The presence of relatively strong Lewis acidic and/or basic sites in the P-free catalyst should be responsible for the formation of C-alkylation products. The weak acid-base characteristics of the catalysts are favourable for the mono-O-methylation of catechol. In comparison with the Lewis acidic sites, the Br(o)nsted acidic sites on the catalysts are more active for the title reaction.