Effects of the Pore Structure and Acid-Base Property of X Zeolites on Side-Chain Alkylation of Toluene with Methanol

One of the potential processes for making styrene monomers is side-chain alkylation of toluene with methanol, and X zeolites (a common type of faujasite) have been identified as one of the most suitable catalysts for this reaction. In this work, a series of X zeolites with different micro- and meso-porosities and acid-base properties are prepared by post-treatments of NaX zeolite and their catalytic performances for the side-chain alkylation of toluene with methanol are evaluated. This study shows that intracrystalline mesopores could be introduced into the NaX zeolite while retaining adequate microporosity through controlling the intensity and sequence of ammonium-exchange (AE) and/or dealumination (DA) post-treatments. The loss in basicity of the resulting mesoporous X zeolites due to AE and/or DA treatments could be compensated and even enhanced by the subsequent cesium modifications. As catalysts for the side-chain alkylation reaction, the study shows that while introducing appropriate mesopores into X zeolites enhances molecular diffusion, the restriction effect of micropores is proven to be critical for their catalytic activity. Moreover, it is the acid-base property rather than the pore structure of the post-treated X zeolites determining their catalytic activity and selectivity for the side-chain alkylation reaction.