Cooperation of Ni and CaO at Interface for CO2 Reforming of CH4: A Combined Theoretical and Experimental Study

Dry reforming of methane (DRM) is a promising chemical approach to convert greenhouse gases CO2 and CH4 into valuable fuels. Previous experimental study has shown that the addition of alkaline earth can promote the activity and stability of the Ni-based catalyst. However, the physical structure of alkaline earth additives on supports and their interaction with Ni particles should have significant influence for the catalytic performance of catalysts. To clarify the synthesis-structure-activity relationship for further improving these catalysts, the underlying reaction mechanism for DRM over size-confined Ni-CaO catalysts on neutral supports and the structure/effect of CaO as promoter were investigated combining density functional theory (DFT) calculation and experimental studies. The favored active sites for all elementary reactions were identified, and the activation energies of the reactions were calculated for the determination of the primary reaction pathways. DFT results found a cooperation effect between Ni and CaO, where the interface dissociates CO2, Ni activates CH4 dehydrogenation, and CaO attracts CO2. The interface between Ni and CaO was found to provide another channel to activate CO2 and decrease the energy barrier of CHO formation, contributing to the high efficiency and long-term stability of the catalyst. On the basis of the DFT results, the optimum stacking order between Ni and CaO was proposed, in good agreement with the experimental studies that synthesized and compared four catalysts with different Ni-CaO structures. The proposed Ni-CaO composite catalyst should be a promising catalyst for potential application in industrial dry reforming processes.