A comparative study of nickel–silica catalyst architectures for CO2 methanation: insights into structure–performance relationships

Abstract

An attractive alternative for CO₂ utilization is its conversion into methane via the CO₂ hydrogenation reaction. Catalysts with different structures represent promising materials for achieving higher CO₂ conversions and CH₄ selectivity. Four distinct nickel–silica catalysts were synthesized using different methods. High-resolution microscopy combined with EDS analysis confirmed the diverse structural features of the catalysts: a supported material (SUP), an encapsulated (embedded) structure (EMBD), a multi-core–shell morphology (SPHERE), and a nanoring morphology (RING). X-ray fluorescence (XRF), X-ray diffraction (XRD), Hydrogen Temperature-Programmed Reduction (H₂-TPR), nitrogen physisorption, and in situ DRIFTS revealed the distinct properties of these materials and provided insights into their internal structures and reaction mechanism. All catalysts showed the formation of well-dispersed nickel particles, with diameters in the range of 2–3 nm. The embedded catalyst stood out due to its stronger metal–support interaction and an encapsulated structure, which were attributed to its specific synthesis method. These characteristics contributed to its superior CH₄ selectivity (83.35%) for the CO₂ hydrogenation reaction at 300 °C, 1 atm, a CO₂ : H₂ ratio of 1 : 4, and a GHSV of 120 000 mL g_cat⁻¹ h⁻¹. At 14 833 mL g_cat⁻¹ h⁻¹, the EMBD catalyst remained stable for 50 h, with 60% CO₂ conversion and a methane selectivity of 97%. The ability of the EMBD catalyst to direct the reaction toward methane was related to the combination of the encapsulation effect and the presence of nickel phyllosilicates, which strengthened metal–support interactions while also facilitating CO re-adsorption and conversion to methane.