Diffusion studies using methane to investigate the diffusional constraint in ZSM-5 samples used in the methanol-to-hydrocarbons reaction

Methanol-to-Hydrocarbons (MTH) is an important industrial reaction. It is thought to work through a 'hydrocarbon pool' mechanism where the hydrocarbons retained within the catalyst pores act both as the activating and deactivating species. It is known that the hydrocarbons retained within the pores increase with time-on-stream and thereby change the diffusion pathways of both reactants and products. During a previous QENS beam allocation, both methanol and methane were used as a probe molecule. The methanol turned out to be immobile even in a reacted catalyst due to strong interactions with the acid sites whereas the methane, showed mobility but the temperatures chosen were outside the IRIS timescale. Methane is inert in ZSM5 and has been shown to be mobile, and choosing the right temperatures will help us study the diffusional characteristics of an active and deactivated MTH catalyst.