The biomass-conversion process has emerged as a renewable and carbon-neutral alternative to traditional fossil resources for producing chemicals and fuels. Nevertheless, for upgrading to liquid fuels and chemicals, extensive removal of oxygen-containing functionalities in biomass derivatives is required. In this context, dehydration, hydrogenation, and hydrogenolysis have been critical reactions for transforming biomass-derived oxygenates, e.g., alcohols, acid, ketone, aldehyde, furan.<br/>  For dehydration of alcohols, various acid catalysts, featured either or both Brønsted (BAS) and Lewis acid sites (LAS), have been employed. Zeolites are widely used as catalysts owing to their well-defined pore structure and BAS and LAS leading to high activity. To understand acid-catalyzed reactions in the micropore of zeolite catalysts, unraveling the molecular environment in the micropore of zeolite catalyst is crucial. Kinetic studies of HMFI-catalyzed dehydration of 1-propanol indicate that the rates for production of propene and dipropyl ether depend critically upon the concentration of either the monomer or the dimer 1-propanol species adsorbed on BAS. However, the structures of these relevant surface species remain unknown.<br/>  In this talk, I will present our study of (i) AIMD-based adsorption free energetics and adsorption isotherm of gas-phase 1-propanol on HMFI, and (ii) the structure of Al T-site after 1-propanol adsorption in HMFI obtained from in situ Al K-edge XAS, ensemble-averaged TD-DFT XANES and MD-EXAF calculations. This study demonstrates that the combination of the in-situ XAS and advanced computation can follow the changes in the environment about a BAS site as the thermodynamics conditions are varied. This provides an unprecedently detailed understanding of the speciation of organics around active sites within a zeolite pore.

Structure and adsorption free energetics of 1-propanol on Al T-site of zeolites from AIMD and XAS study

ACS Spring 2022

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