Methane dry reforming on N-doped carbon-supported Mo₂C catalysts: Impacts of N functionality and Ni addition

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Abstract

Nitrogen-doped carbon (NC)-supported Mo and Ni-Mo catalysts were synthesized via pyrolysis and impregnation strategies to investigate their performance in methane dry reforming (DRM). By modulating nitrogen content (1.65–13.25 at.%) and speciation (pyridinic/pyrrolic vs. graphitic N) in NC supports, we demonstrated that nitrogen functionalities critically influence MoO₂ reduction and Mo₂C stabilization. Higher N content in NC₂ and NC₃ enhanced metal-support interactions, promoting Mo₂C formation during H₂ reduction, while NC₁ (low N) favored metallic Mo. However, under DRM conditions, all catalysts deactivated due to Mo₂C oxidation to MoO₂, with stability marginally improved at 850 °C via improved "oxidation-re-carbonization" cycles. Introducing Ni (5–15 wt.%) via impregnation facilitated CH₄ dissociation and lowered MoO₂ reduction temperatures through hydrogen spillover, boosting initial CH₄/CO₂ conversions and H₂/CO ratios. Yet, Ni incorporation accelerated carbon support degradation (>50% mass loss) and induced inactive phases (NiO, Ni₃Mo₃N), offsetting its promotional effects. Combined XRD, H₂-TPR, Raman, and XPS analyses revealed the interplay between N defects, Mo speciation, and Ni-Mo interactions, underscoring the challenges in balancing activity and stability. This study highlights the dual role of nitrogen in stabilizing active phases and the limitations of Ni-Mo bifunctionality under oxidative DRM conditions, providing critical insights for designing robust, carbon-supported catalysts through defect engineering and structural optimization.