Influence of Surface Formate Species on Methane Selectivity for Carbon Dioxide Methanation over Nickel Hydroxyapatite Catalyst

Absence of mechanistic understanding of carbon dioxide (CO2) methanation reaction on nickel hydroxyapatite (NiHAP) and the nature of nickel chemical state hampers the enhancement of catalytic activity and selectivity for such material. A varying amount of oleic acid (OA) addition on NiHAP is found to have a strong influence on the chemical state of nickel as evidenced from x-ray spectroscopy (XPS) and x-ray absorption spectroscopy (XAS). The chemical state of nickel influences the amount of surface intermediate species which affects methane formation as observed in infra-red spectroscopy. This suggests that varying amount of OA can influence the chemical state of nickel which is important in influencing the type of reaction intermediates on the NiHAP surface. Langmuir-Hinshelwood model is validated for proposed reaction mechanism for the better performing catalyst. The findings reported here is useful for designing a hydroxyapatite-based catalyst for CO2 utilization.