Diffusion of Methanol in Zeolites: a Molecular Dynamics Study

Methanol is an important feedstock in numerous catalytic processes. It can be produced via Fischer-Tropsch reaction from synthesis gas [1] and its further transformation to hydrocarbons up to C10 is the basis of several industrially important reactions as for instance the Methanol to Gasoline process [2]. Methanol can also be used as an alkylating agent for aromatic compounds in zeolite-catalysed reactions. This reaction takes place in a number of basic zeolites, including alkali metal-exchanged X and Y zeolites. The optimisation of such processes demands a sophisticated understanding of the interactions between the zeolite surfaces and the reactant methanol molecules, including the transport properties of the reagent within the catalyst micropores. Here we investigate the microscopic diffusion mechanism of this adsorbate in the zeolites NaY by means of molecular dynamics simulations. To achieve this, a new potential for reproducing the interaction between the extra-framework cations Na and the oxygen of methanol was derived from our results of ab initio calculations [3]. The resultant forcefield was then used to carry out the NaY molecular dynamics calculations. These results were then compared with those obtained for the purely siliceous zeolite Y (DAY) in order to emphasise the difference in methanol diffusion in a “cation-free” zeolite.