Gas-phase O-methylation of catechol with dimethyl carbonate over SBA-15-supported aluminum phosphate catalyst

Abstract

SBA-15-supported Al₂O₃-P₂O₅ with 10 wt% Al₂O₃ and different P₂O₅ mass percentages (10Al₂O₃-xP₂O₅/SBA-15) were prepared by simple impregnation method and used for gas-phase selective O-methylation of catechol to guaiacol with dimethyl carbonate. The 10Al₂O₃-xP₂O₅/SBA-15 catalysts maintained ordered mesoporous structures, but their specific surface areas, pore volumes, and pores decreased with the addition of Al and P oxides. The addition of P₂O₅ decreased the strength of weak acid, but with the P₂O₅ content increasing, the additional pseudo-bridging bonds that are similar to amorphous silica-alumina were formed, which enhanced the acidity of weak acid. Brønsted acid sites introduced by P₂O₅ promoted more acid sites and lower the strength of acid sites. The basic sites increased with the increase of P₂O₅ content. Acidic sites are the key to control the catalytic activity, and basic sites are the key to control the catalytic selectivity. 10Al₂O₃-5P₂O₅/SBA-15 exhibited excellent catalytic activities and high selectivity to guaiacol for the O-methylation of catechol, due to the synergistic effect of acid and base sites.