Ethylcyclohexane Hydroconversion in EU-1 Zeolite: DFT-based Microkinetic Modeling Reveals the Nature of the Kinetically Relevant Intermediates

The transformation of cycloalkanes is a key-reaction in refining and petrochemistry. Herein, we unravel the mechanism and the kinetics of the transformation of ethylcyclohexane, considering a bifunctional catalyst composed of platinum and of the EU-1 zeolite, by experiments, density functional theory (DFT) calculations and DFT-based microkinetic modeling. The simulated mechanisms involve carbenium intermediates. DFT shows the central kinetic role of the pi-complexes corresponding to secondary carbenium ions. Cycle contractions and expansions appear to be rate-limiting. The DFT-based microkinetic model includes a limited number of kinetic parameters optimized by regression with respect to the experimental data. The agreement with experimental results is very good, showing that the mechanisms proposed, the nature of the intermediates, and the values of the computed rate constants, are relevant. The reaction starts by the cycle contraction of 1-ethylcyclohexene, then shifts to a second sequence of cycle expansion-contraction reactions by intercalated methyl-shifts.

Automated summary

The mechanism and kinetics of the transformation of ethylcyclohexane using a bifunctional catalyst of platinum and EU-1 zeolite were studied through experiments, DFT calculations, and microkinetic modeling. The mechanism involves carbenium intermediates with pi-complexes playing a central kinetic role. The agreement between the DFT-based microkinetic model and experimental data was very good, confirming the relevance of the proposed mechanisms and computed rate constants.