The Alkylation\nof Phenol with Methanol: The Influence\nof Acid–Base Properties of X Zeolite on the Selectivity of <i>para</i>- and <i>meta</i>-Cresol

The vapor-phase alkylation of phenol with methanol was\ninvestigated\non X zeolites and modified X zeolites. First, the difference of product\ndistribution was tested between acid zeolite (HZSM-5, HX, HMCM-22,\nand Hβ) and basic zeolite X (KX and CsX). Then, X zeolites were\nmodified with Li, K, Cs, Ca, Mg, La, and Ce ion exchange to adjust\nthe acid–base properties of the zeolites. Finally, the type\nof acid sites and strength of acid–base sites on zeolite catalysts\nwere determined by characterization techniques such as Py-IR and TPD,\nand the alkylation of phenol with methanol was tested. The results\nshowed that O-alkylation products convert to the C-alkylation products\non the B acid sites, which enhances the isomerization reaction, thereby\nincreasing the proportion of <i>meta</i>-cresol in cresol.\nThe results of TPD and IR indicated that weak basic sites on the zeolite\npromote the vertical adsorption of the aromatic ring and strong basic\nsites promote side-chain activation, while acid sites determine whether\nring substitution or side-chain substitution occurs. During the reaction\nof phenol with methanol, the phenolic hydroxyl group strongly interacts\nwith the surface of zeolites, leading to differences in the adsorption\nmode of the aromatic ring (vertical or parallel), which, in turn,\nalters the position of alkyl substitution. It is found that the proper\nacid–base property of X zeolites can selectively determine\nthe desired alkylated products.