Ab initio selection of zeolite topology for biomass conversion to para-xylene based on transition state selectivity

Abstract

Recent reports have pointed out a sustainable and highly selective formation route via the Diels–Alder (DA) cycloaddition between biomass-derived 2, 5-dimethylfuran (DMF) and ethene over zeolitic catalysts to produce para-xylene (p-xylene). Here, a systematic multi-scale simulation was carried out to identify candidate zeolite frameworks with potentially better catalytic activities than previously reported catalysts, through a combination of “ab initio” synthesis, thermodynamic and kinetic analysis, and adsorption/diffusion simulations. We first screened representative zeolites based on the limiting dimensions of their voids (windows, cages, channels) for reactants and products, the extent of stabilization of the key transition states by organic structure directing agents, and the synthesis difficulty informed by literature knowledge. Subsequently, the intrinsic and apparent free energy barriers of the rate-determining step (i.e., cycloaddition) obtained from density functional theory calculations were used to predict reaction kinetics of the potentially useful zeolites. Finally, three final candidates (MOR, MOZ, and IFR) and two experimentally validated zeolites (FAU and BEA) were employed to compare the adsorption and diffusion performance of DMF and p-xylene as the final criterion by grand canonical Monte Carlo and molecular dynamics simulations. In summary, MOR shows the fastest diffusion, IFR shows the lowest apparent energy barrier, and MOZ shows the lowest intrinsic energy barrier. Altogether, this study not only predicts MOR, IFR, and MOZ zeolites to have a good catalytic performance for the DA-dehydration process of DMF and ethene to p-xylene but also illustrates the potential of ab initio selection, through combined theoretical assessments of adsorption, reaction and diffusion, for the rational selection and design of optimal catalysts for targeted catalytic transformations.