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

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 degrees C, above 40 % CO2 conversion and essentially 100 % methane selectivity could be achieved at a reaction temperature of 200 degrees C (P = 1 bar and GHSV = 8,000 mL & sdot;gcat.- 1 & sdot;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.