Influence of Aluminium Doping on the Performance of Ni/HAP Catalyst in Dry Reforming of Methane

Dry reforming of methane (DRM) is a crucial route for the comprehensive utilization of CH4 and CO2 to produce synthesis gas. However, carbon deposition and sintering of active metals remain the primary challenges facing DRM catalysts. In this study, a series of aluminum (Al)-doped hydroxyapatite (HAP) supports were synthesized via co-precipitation, and the corresponding supported Ni/Al-HAP catalysts were prepared by the impregnation method. The influence of Al doping content on the catalyst structure, surface properties, and DRM performance was systematically investigated. The results indicate that the incorporation of Al3+ into the HAP lattice induces lattice distortion, which synergistically modulates the physicochemical properties of the catalyst in three aspects: (1) In terms of physical structure, it optimizes the pore structure, increasing the specific surface area and pore volume; (2) In terms of metal-support interaction, it enhances the interaction strength between Ni and the support, reducing the Ni particle size; (3) In terms of surface chemistry, it increases the number of acidic sites and weak basic sites, while decreasing the number of strong basic sites. These synergistic structural optimizations enhance the activity and stability of the catalyst. However, characterizations such as TG-DSC, Raman, TPD, and TPSR reveal that Al doping does not inhibit carbon deposition. Instead, the reduction in Ni particle size and the increase in surface acidic sites promote the deep cracking of CH4, while the decrease in the number of moderate CO2 adsorption sites leads to insufficient activation of CO2 into carbonates, resulting in increased carbon deposition. In situ infrared spectroscopy indicates that Al doping promotes the formation of key intermediates (HCO3* and CO3*) but does not alter the activation pathway of the reactants. We propose that Al doping is an effective strategy for enhancing reactant conversion and stability; however, addressing the issue of carbon deposition requires further modulation of the catalyst's surface chemistry to optimize the CO2 activation pathway.