Inhibition of Xylene Isomerization in the Production of Renewable Aromatic Chemicals from Biomass-Derived Furans

Inhibition of p-xylene isomerization in the presence of H-Y (Si/Al 2.6) and H-BEA (Si/Al 12.5) zeolites was studied under conditions relevant to p-xylene production from 2,5-dimethylfuran (DMF) and ethylene. Through examination of the reaction components, it was shown that both DMF and 2,5-hexanedione inhibit transalkylation and methyl shift reactions of p-xylene, while other reaction components, water and ethylene, do not. Retention of Bronsted acid sites after the reaction was shown through the use of ²⁷Al NMR for both H-Y and H-BEA zeolites, but with a reduction in the ratio of tetrahedrally coordinated aluminum (strong acid sites) to octahedrally coordinated aluminum (Lewis acid sites) coinciding with the disappearance of the framework aluminum. Diffuse reflectance spectroscopy has shown preferential adsorption of DMF and 2,5-hexanedione (DMF + H₂O) relative to p-xylene to the Bronsted acid sites located in the super and sodalite cages of the H-Y. Desorption characteristics for DMF and p-xylene in H-Y and H-BEA were determined by thermogravimetric analysis, consistent with adsorption energetics of individual chemical species and dimeric complexes evaluated by an ONIOM method. Evaluation of three mechanisms, allowing for production of p-xylene from DMF and ethylene while also inhibiting p-xylene isomerization, supports high surface coverage of the active site with 2,5-hexanedione, supported by electronic structure calculations.