This proposal will use QENS to investigate the diffusion of propane and methylacetate in mordenite zeolite catalysts used for the carbonylation of dimethylether to make methylacetate. The project is supported by a Royal Society International Collaboration Grant between Aberdeen University and Tianjin University China. The objective is to understand the causes of catalyst deactivation in this process. Propane is chosen as a non-reactive simulant of the dimethylether reactant; we will investigate how propane diffusion in mordenite is influenced by pretreatment of the catalyst with pyridine, which is believed to partially block zeolite pores and enhance catalyst lifetime. We will also study the diffusion of the product molecule methylacetate in both untreated and pyridine treated catalysts, to determine if inhibition of product diffusion out of the pores enhances catalyst deactivation.