Renewable production of p-xylene from [4 + 2] Diels− Alder cycloaddition of 2,5-dimethylfuran (DMF) and ethylene with H−Y zeolite catalyst in n-heptane solvent is investigated. Experimental studies varying the solid acid catalyst concentration reveal two kinetic regimes for the p-xylene production rate: (i) a linear regime at low acid site concentrations with activation energy E a = 10.8 kcal/mol and (ii) a catalyst-independent kinetic regime at high acid site concentrations with activation energy E a = 20.1 kcal/mol. We carry out hybrid QM/MM calculations with a three-layer embedded cluster ONIOM model to compute the energetics along the main reaction pathway, and a microkinetic model is constructed for the interpretation of the experimental kinetic data. At high solid acid concentrations, p-xylene production is limited by the homogeneous Diels−Alder reaction, whereas at low acid concentrations, the overall rate is limited by the heterogeneously catalyzed dehydration of the Diels−Alder cycloadduct of DMF and ethylene because of an insufficient number of acid sites, despite the dehydration reaction requiring significantly less activation energy. A reduced kinetic model reveals that the production of p-xylene follows the general kinetics of tandem reactions in which the first step is uncatalyzed and the second step is heterogeneously catalyzed. Reaction orders and apparent activation energies of quantum mechanical and microkinetic simulations are in agreement with experimental values.

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The zeotypic Lewis acids Sn‐BEA, Zr‐BEA, and Ti‐BEA have recently been reported to catalyze the synthesis of p‐xylene by dehydrative aromatization of the Diels–Alder product between 2,5‐dimethylfuran and ethylene. Although it has been shown that these Lewis acids can catalyze the dehydration of the Diels–Alder cycloadduct, the tandem scheme precludes decoupling of the two steps needed to infer whether these same catalysts can catalyze the Diels–Alder step. We have employed electronic structure calculations and microkinetic modelling to investigate the Diels–Alder aromatization of 2,5‐dimethylfuran and ethylene to p‐xylene over the Lewis‐acidic zeotypes Sn‐, Zr‐, and Ti‐BEA. We show that there is only minor catalysis of the Diels–Alder reaction, solely attributable to confinement phenomena varying with the translational freedom allowed to the species inside the zeolite. Microkinetic modelling and sensitivity analysis of the computed rates show that the heterogeneous Diels–Alder pathway does not contribute to the overall rate, and that the homogeneous cycloaddition is rate‐limiting at high acid site concentrations. Only the partially hydrolyzed (“open”) Lewis acid sites are found to be catalytically active, with moderately Brønsted‐acidic silanol groups formed, which catalyze 2,5‐dimethylfuran hydrolysis. Of the Lewis acids tested in this work, Zr‐BEA and Sn‐BEA have similar activities, in agreement with experiment, whereas Ti‐BEA is found to be inactive, suggesting that the recently reported Ti‐BEA activity was likely a result of Brønsted‐acidic defect sites.