Ceria-modified high pore volume Ni/Al2O3 spheres for enhanced low-temperature CO2 methanation

Abstract

CO₂ transformation poses a key challenge due to its thermodynamic stability and chemical inertness. Low-temperature methanation offers near-equilibrium CO₂ conversion to methane at ambient pressure, a promising strategy for carbon neutrality. However, effectively catalyzing CO₂ activation at low temperatures presents a key challenge due to the kinetic constraints of the hydrogenation intermediates. This study investigates the influence of high pore volume and Ce loading on the catalytic performance of Ni/Al₂O₃ spheres prepared by the wet impregnation method. Initially, high pore volume Al₂O₃ spheres were synthesized in microchannels, and their catalytic performance was compared with that of two commercially available Al₂O₃ supports. Ni/Al₂O₃ spheres with high specific surface area (267 m²/g) and pore volume (0.97 mL/g) showed 73 % CO₂ conversion compared to 59 % and 55 % on commercial-1 and commercial-2 supports at 325 °C and a GHSV of 16000 mL⋅g_cat⁻¹⋅h⁻¹. Then, various amounts of Ce were doped on Ni/Al₂O₃ spheres to further enhance CO₂ methanation performance, and results revealed NiCe_7.5/Al₂O₃ possessed 86 % CO₂ conversion, 99.9 % CH₄ selectivity and a methane STY of 122 mmol. gcat⁻¹.h⁻¹ at 250 °C. Advanced in-situ characterization approaches, featuring in-situ Raman, quasi in-situ XPS, and HAADF-STEM revealed that the incorporation of Ce promotes Ni dispersion, decreases particle size, and promotes abundant oxygen vacancies resulting in efficient CO₂ methanation. In-situ DRIFTS and DFT studies revealed that the NiCe_7.5/Al₂O₃ follows the CO₂ hydrogenation formate pathway to produce CH₄. This efficient low-temperature CO₂ methanation demonstrates the superior catalytic performance is associated with higher pore structure and Ce doping on Ni/Al₂O₃ spheres.