Investigation into the coking-related key reaction steps in dry reforming of methane over NiMgOx catalyst

Abstract

With pre-reduced NiMgOx catalyst, the structure evolution, catalytic performance, surface species and coking-related reaction steps are investigated in methane dry reforming (DRM) at selected temperatures. Satisfactory conversion of CH4 and CO2, H2/CO ratio, and anti-coke stability are achieved in long-term (78 h) reaction at 650 °C as a proper temperature. The characterizations evidence co-existence of metallic Ni0 and solid solution phases in the working catalysts. Combined catalytic evaluation and coke analysis reveal that, at 650 °C, endothermic CO2-free CH4 decomposition shows a high initial rate for H2 production but severe coke deposition for rapid deactivation, serving as the primary coking process. In contrast, exothermic CO disproportionation exhibits a lower reaction rate and a higher coke graphitization degree. The in-situ DRIFT spectra demonstrate that carbonates and bicarbonates serve as the primary adsorbates during CO2 dissociation process, whereas formate intermediates dominate in DRM reactions. Such evolution of the surface species verifies facile dissociation of both CH4 and CO2 in well-matched rates, promoting coke-resistance DRM reaction over NiMgOx catalyst.