This proposal examines the diffusion behaviour of olefin hydrocarbons adsorbed in microporous zeolite catalysts. It builds on a previous study which has shown that simulated aging of the catalyst results in changes to the diffusion behaviour of the adsorbed species and seeks to distinguish how each aspect of the aging-related alterations to the zeolite contribute to the overall change in olefin diffusion. These differences in diffusion are a key factor in determining the selectivity of the catalyst toward different reaction pathways, which makes important contributions to its commercial application in both catalytic cracking and methanol-to-gasoline processes.