Insight into the topology effect on the diffusion of ethene and propene in zeolites: A molecular dynamics simulation study

Selectivity control is a difficult scientific and industrial challenge in methanol-to-olefins (MTO) conversion. It has been experimentally established that the topology of zeolite catalysts influenced the distribution of products. Besides the topology effect on reaction kinetics, the topology influences the diffusion of reactants and products in catalysts as well. In this work, by using COMPASS force-field molecular dynamics method, we investigated the intracrystalline diffusion of ethene and propene in four different zeolites, CHA, MFI, BEA and FAU, at different temperatures. The self-diffusion coefficients and diffusion activation barriers were calculated. A strong restriction on the diffusion of propene in CHA was observed because the self-diffusion coefficient ratio of ethene to propene is larger than 18 and the diffusion activation barrier of propene is more than 20 kJ/mol in CHA. This ratio decreases with the increase of temperature in the four investigated zeolites. The shape selectivity on products from diffusion perspective can provide some implications on the understanding of the selectivity difference between HSAPO-34 and HZSM-5 catalysts for the MTO conversion.

Graphical AbstractThe diffusion of ethene and propene in four zeolites (CHA, MFI, BEA and FAU) was investigated using molecular dynamics simulation. CHA exhibits strong restriction for the diffusion of propene.Figure optionsDownload as PowerPoint slide