Nickel/Molybdenum Bimetallic Alloy for Dry Reforming of Methane: A Coverage-Dependence Microkinetic Model Simulation Based on the First-Principles Calculation

Ni-based catalysts have attracted much attention because of their high catalytic activity for dry reforming of methane (DRM) reaction and their low-cost characteristics. The deactivation caused by carbon deposition has become a major factor restricting its application. Mo doping is expected to improve the carbon deposition resistance of Ni-based catalysts. In this study, we used density functional theory (DFT) calculations and the microkinetic model to compare the catalytic activity of Ni and MoNi 4 (as a Mo-doped Ni-based catalyst model) for the DRM reaction. By calculating the surface energies, Ni(111) and MoNi 4 (001) were determined as the calculation models. The DFT calculation results show that MoNi 4 catalyst has a stronger adsorption capacity for intermediate species. Combining Bader charge analysis and charge density differences analysis, the stronger adsorption capacity comes from the stronger electron donating capacity brought about by the doping of Mo. According to our proposed reaction network, the energy barriers of 19 elementary reactions were calculated in detail. We found that there are similar CO 2 dissociation modes (direct dissociation) and C–O bond formation modes (CH 2 /CH–O oxidation) on Ni(111) and MoNi 4 (001). Both CH 4 dissociation and CO 2 dissociation on MoNi 4 (001) have a lower energy barrier, while CO formation through CH 2 /CH–O oxidation has a higher energy barrier. The total free energy barrier of the DRM is lower than that of carbon deposition formation on MoNi 4 (001), whereas the opposite on Ni(111), means MoNi 4 (001) shows strongly carbon resistance properties. At 1073.15 K and 2 bar, the microkinetic simulation results showed that when the reaction reaches equilibrium, MoNi 4 (001) is deactivated due to excessive O*. Accordingly, the influence of O* coverage on the activation energy of CO 2 dissociation was considered in the MoNi 4 microkinetic model. In this way, the DRM reaction can be carried out steadily and continuously on MoNi 4 (001). And the simulation results show that MoNi 4 catalyst has extremely high catalytic activity and selectivity and is basically not affected by carbon deposition and byproduct H 2 O. Under the same simulated conditions, MoNi 4 (001) showed better catalytic activity than Ni(111). In addition, degree of rate control (DRC) analysis showed that on MoNi 4 (001), the activation of CH 4 is the rate-limiting step of the whole reaction. Through our study, one might be proposed that alloying Ni with a small amount of active metals such as Mo can increase the carbon deposition resistance by increasing the activation of CH 4 and CO 2 in an equal ratio.