First-principles microkinetic analysis of dehydrogenation of cyclohexene on the Pt/Cu/Pt (111) surface
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ORIGINAL PAPER
First-principles microkinetic analysis of dehydrogenation of cyclohexene on the Pt/Cu/Pt (111) surface Shou Chun Feng 1 & Hong Yan Ma 1 & Peng Peng Hao 1 Received: 25 January 2020 / Accepted: 23 March 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Three kinds of Pt-Cu bimetallic catalysts (Cu/Pt (111), Pt/Cu/Pt (111), and Pt4Cu5/Pt (111)) have been researched employing density functional theory (DFT) calculation, using dehydrogenation of cyclohexene to benzene as a probe reaction. The adsorption energies are basically in the sequence: Pt4Cu5/Pt (111) > Cu/Pt (111) ≈ Pt/Cu/Pt (111). The key step is C6H9 → C6H8 on Cu/ Pt (111) (0.85 eV) and Pt/Cu/Pt (111) (0.87 eV). On Pt4Cu5/Pt (111), the key step is C6H7 → C6H6 (1.17 eV). The selectivity for gas phase benzene is in the order of Cu/Pt(111) > Pt/Cu/Pt(111) > Pt4Cu5/Pt(111), according to the energy difference between the barrier of benzene dehydrogenated to phenyl and benzene desorption. The co-adsorbed hydrogen atoms lead to improved selectivity for gas phase benzene on Cu/Pt (111) and Pt/Cu/Pt (111), by making benzene desorption easy but dehydrogenation difficult. However, the barrier of benzene dehydrogenation decreases with the increase of H coverage on the Pt4Cu5/Pt (111) due to obvious destabilized benzene, and thus the effect on Pt4Cu5/Pt (111) is closely related to the concentration of surface H. Attributed to thermodynamic stability, high activity, and selectivity for gas benzene, the Pt/Cu/Pt (111) structure is suggested as reasonable dehydrogenation catalyst, and the dehydrogenation process on Pt/Cu/Pt(111) has been further studied by microkinetic modeling. A volcano-like relationship is found between the adsorption of cyclohexene and the TOF (turnover frequency) of gas phase benzene. Secondly, two apparent activation energies are obtained: 0.77 eV (250~350 K) and 0.45 eV (350~650 K), implying the RDS (rate-determined step) changes with temperature. Keywords Microkinetic simulation . Cyclohexene dehydrogenation . Turnover frequency . Pt-Cu bimetallic catalyst
Introduction Cyclohexene is a raw material in organic synthesis, and it could be used as solvent, extractant, and stabilizer. The dehydrogenation of cyclohexene to benzene on the single crystal Pt
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00894-020-04363-y) contains supplementary material, which is available to authorized users. * Shou Chun Feng [email protected] Hong Yan Ma [email protected] Peng Peng Hao [email protected] 1
Tianjin University, RenAi College, Tianjin 301636, People’s Republic of China
surface is a typical catalytic reforming process, which has been investigated by various surface science methods [1–5]. A sequential dehydrogenation mechanism [1] was suggested. The π-allyl c-C6H9 [1–3] and cyclohexadiene [1, 2] were found as meta-stable intermediates. The Pt was so active that the carbons were produced by 800 K [5], which deactivated the Pt catalyst. Recently, an experiment
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