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Here, 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 Brønsted 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 coordinatedmore » 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 Brønsted 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.« less