Natural kaolin-derived ruthenium-supported nanoporous geopolymer: a sustainable catalyst for CO2 methanation

To address the serious concern of excessive CO<inf>2</inf> emissions, the conversion of environmental CO<inf>2</inf> into methane via a CO<inf>2</inf> methanation reaction is promising. Methane can be used not only as a fuel but also as a hydrogen carrier. In this study, a geopolymer synthesized using natural kaolin (GNK) is explored as a support. This geopolymer support was used to disperse ruthenium (Ru) nanoparticles through a single-step hydrazine reduction method. The catalyst was characterized using various surface and bulk techniques. Furthermore, the catalytic performance of the ruthenium-supported geopolymer (Ru/GNK) for the CO<inf>2</inf> methanation process was explored with different Ru loadings (%) and at different flow rates. Catalyst stability was also investigated for 20 h by a time-on-stream isothermal experiment. The spent catalyst was characterized by O<inf>2</inf>-temperature programmed oxidation (O<inf>2</inf>-TPO) and X-ray photoelectron spectroscopy (XPS). Overall, the catalyst proved to be cost-effective and free from pretreatment requirements, in addition to exhibiting superior activity, high selectivity, and good stability.