Effect of NaOH content in the synthesis gel on the catalytic performance of H-ZSM-5 zeolites in the gas phase carbonylation of dimethoxymethane

A series of H-ZSM-5 zeolites were prepared by changing the NaOH content in the synthesis gel and their catalytic performance in the vapor-phase carbonylation of dimethoxymethane (DMM) to produce methyl methoxyacetate (MMAc) was investigated. The results indicate that the H-ZSM-5 zeolite prepared with the synthesis gel containing 0.81% NaOH exhibits the highest catalytic activity in the vapor-phase DMM carbonylation. Various characterization results of nitrogen sorption, 27Al NMR, NH3-TPD and Py-FTIR illustrate that both the medium-strong Bronsted acid sites and mesoporous volume are crucial factors in promoting the carbonylation of DMM over H-ZSM-5, which can be effectively regulated by changing the NaOH content in the synthesis gel. The increase of medium-strong Bronsted acid sites can raise the DMM conversion by providing more active acid sites, whereas the mesopores can improve the selectivity to MMAc by shortening the product diffusion path, weakening the steric constraints and suppressing the side reactions. The density functional theory calculation further illustrates that ZOCH2OCH3 intermediate is formed upon the decomposition of DMM on H-ZSM-5; based on this observation, a possible reaction mechanism for the formation of MMAc was then proposed.