Methane dehydrogenation and oxidation process over Ni-based bimetallic catalysts

Abstract

The possible reaction path for methane dehydrogenation and oxidation process on three Ni-based bimetallic catalysts (Ni2, NiCo and NiCu) was investigated in detail by using the density functional theory (DFT) calculation with the B3LYP method. In addition, the optimized geometric structures, activation energies and reaction rate constants were evaluated to compare the differences between the three Ni-based bimetallic catalysts. The results indicate that the reaction path on NiCo and Ni2 are the same to each other but very different from that on NiCu. The reaction path on Ni2 and NiCo is mainly based on O as oxidant, with a smaller barrier. While the reaction path on NiCu is OH, with a larger barrier. The methane dehydrogenation and oxidation process on the NiCo catalyst is the same as that on the Ni2 catalyst (CH4 → CH3 → CH2 → CH → CHO → CO → CO2), but different with the reaction path on the NiCu (CH4 → CH3 → CH2 → CH2OH → CHOH → CHO → CO → COOH → CO2). The reaction rate constant for the rate-determining step on the three catalysts follows the order: NiCo (k = 8.63 × 104 s−1) > Ni2 (k = 7.44 × 104 s−1) > NiCu (k = 2.40 × 10−1 s−1). Through the comprehensive comparison, we conclude that NiCo shows better performance than do the other two catalysts in the catalytic combustion of methane, owing to its high activity and high anti-carbon deposition capacity.