Low-temperature CO2 methanation over SiO2 supported Ni catalysts derived from sol-gel precursors: Effect of pretreatment process

Abstract

CO₂ methanation is a promising approach for simultaneously valorizing CO₂ while displacing fossil-derived methane. Although Ni is a well-known earth-abundant methanation catalyst, achieving high activity at low reaction temperatures requires a combination of well-dispersed Ni, proper basicity, and abundant surface oxygen vacancies that is often difficult to achieve over an inert support such as SiO₂. Here, we demonstrate the synthesis of active, selective, and stable SiO₂-supported Ni (Ni/SiO₂) catalysts for low-temperature methanation via the direct H₂ reduction of dried sol–gel precursors. At the optimal H₂ reduction temperature of 400 °C, above 40 % CO₂ conversion and essentially 100 % methane selectivity could be achieved at a reaction temperature of 200 °C (P = 1 bar and GHSV = 8,000 mL⋅g_cat.⁻¹⋅h⁻¹). A comprehensive suite of characterizations revealed well-dispersed Ni together with moderate basicity engendered by Ni-O-Si sites. Notably, these Ni-O-Si sites are lost upon air calcination or partially destroyed under higher-temperature H₂ pretreatment, highlighting the important effect of pretreatment conditions on catalyst performance. Further, in-situ DRIFTS analysis linked the superior performance of the best catalyst to a high concentration of surface carbonyl intermediates. Overall, these findings not only provide valuable insights into sol–gel syntheses and low-temperature CO₂ methanation, but also reveal a simple, scalable, and cost-effective route towards low-temperature methanation catalysts with prospective industrial applications.