Theoretical study on the adsorption and diffusion behavior of methyl oleate catalytic cracking in hierarchical ZSM-5 zeolite

The hierarchical ZSM-5 zeolite has abundant pore structure, and its unique micro-mesopic pore structure can significantly promote the occurrence of macromolecular reactions such as methyl oleate (OAME), while the promotion mechanism and structure-activity relationship at the molecular level are still unclear. In this work, we studied the adsorption and diffusion behavior of the reactants and five product molecules (C3H6, C4H8 and BTX) in the catalytic cracking reaction of OAME via Monte Carlo simulation (MC) combined with molecular dynamics (MD). By analyzing the adsorption isotherms, adsorption density maps and diffusion coefficients of the reacting species, we found that rising temperature was detrimental to the adsorption of OAME, thus inhibiting the reaction, which is consistent with the experimental results. At the same time, the two adsorption sites in the zeolite play significantly different roles. The straight channel provides the aromatization active center in the catalytic creaking reaction, while the role of the hierarchical channel is reflected in promoting the mass transfer and diffusion of the main product molecules of BTX. Such synergistic catalysis effect of hierarchical ZSM-5 zeolite channel increases the BTX yield compared to microporous. In addition, it was found that the main reason why the hierarchical pore ZSM-5 molecular sieve can improve the aromatic yield is that it can accelerate the rapid diffusion of BTX into the mesopores. The above simulation results not only help to determine the experimental conditions of the fatty acid ester catalytic cracking reaction from the microscopic point of view, but also could enrich our understanding of the microcosmic mechanism of hierarchical zeolites for prolific aromatics. © 2024 Materials China. All rights reserved.