Effect of NaOH content for the properties of HZSM-5 zeolites and its catalytic performance on gas phase carbonylation of dimethoxymethane

A series of ZSM-5 zeolites were prepared by changing the NaOH content, and their catalytic performance on the vapor-phase carbonylation of dimethoxymethane (DMM) to synthesize methyl methoxyacetate (MMAc) was investigated detailedly. The results indicate that the ZSM-5 zeolite prepared under the 0.81% NaOH content shows the best catalytic performance. Various characterization results, including BET, ²⁷Al NMR, NH₃-TPD and Py-FTIR, illustrate that medium-strong Brønsted acid sites and mesoporous volume are the chief factors in promoting carbonylation of DMM over ZSM-5 zeolite, which can be effectively regulated by changing NaOH content. The increase of medium-strong Brønsted acid sites can improve DMM conversion by providing more active acid sites; the introduction of mesoporous can increase MMAc selectivity by shortening the product diffusion path, weakening steric constraint of pore walls and suppressing parts of side reactions. Density functional theory was further carried out to study the interaction between DMM and ZSM-5 zeolite. The calculated results find that intermediate species ZOCH₂OCH₃ is formed firstly during DMM decomposition. Based on this, a possible formation mechanism of MMAc was then proposed.