Diffusion Mechanisms and Preferential Dynamics of Promoter Molecules in ZSM-5 Zeolite

29 April 2024, Version 2
This content is a preprint and has not undergone peer review at the time of posting.

Abstract

The diffusion in ZSM-5 zeolite of methanol and of two series of promoters of the methanol to dimethyl ether reaction (linear methyl esters, benzaldehyde, 4-n-alkyl benzaldehydes) has been studied using classical molecular dynamics in the NVT ensemble. Whereas promoter diffusion coefficients decrease with increasing alkyl chain length in methyl esters, the aromatic aldehyde promoters all have similar diffusion coefficients. The lowest diffusion coefficient is that of benzaldehyde. All the promoters exhibit a preference for moving in the straight pore, a preference that is most pronounced for the 4-n-alkyl benzaldehydes and least for the longest aliphatic esters. A novel diffusion mechanism, a molecular ’3-point turn’, is observed. The diffusion coefficient of methanol is larger than that of all the promoters. The more catalytically active aromatic aldehyde promoters limit methanol diffusion less than the aliphatic esters.

Keywords

zeolites
diffusion
promoters
molecular dynamics
simulation

Supplementary materials

Title
Description
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Title
ESI
Description
Electronic Supplementary Information.
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Title
3-point turn
Description
A video of the molecular 3-point turn described in the paper.
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