Ni/Hydroxyapatite Catalysts for CH4–CO2 Reforming: Enhanced Performance Through Impregnation-Induced Structural Carbonation

Hydroxyapatite (CaHAP) has emerged as an attractive support material for Ni-based dry reforming of methane (DRM) catalysts in recent years, owing to its excellent thermal stability and surface basicity. However, the role of its unique anion and cation exchange capabilities in modulating catalyst activity and stability remains poorly understood. In this work, Ni was loaded onto commercial CaHAP by precipitation-impregnation, with the impregnation duration before precipitation systematically varied to probe ion exchange effects on catalytic performance. The results show that simply altering the impregnation time does not significantly promote ion exchange between Ni2+ and Ca2+. However, with prolonged impregnation, the structural −OH and PO43– in CaHAP are progressively replaced by CO32–. This carbonation process strengthens the metal–support interaction (MSI) and improves Ni dispersion, leading to enhanced CH4 conversion. Meanwhile, the incorporation of CO32– is equivalent to directly implanting chemisorbed CO2 into the support structure, which markedly enhances its adsorption and activation capacity. Under the relatively harsh reaction conditions of T = 700 °C and WHSV = 48,000 mL·gcat–1·h–1, CH4/CO2 = 1:1 without inert gas dilution, the 5NC-6h catalyst with the longest impregnation time achieves the highest CH4 and CO2 conversions (70.3% and 80.6%, respectively), while exhibiting surface deposited carbon with the lowest degree of inertness. This work reveals that prolonged impregnation unexpectedly induces CaHAP carbonation, a straightforward route to synergistically enhance DRM performance.