Preparation of Sustainable Ni/SiO₂ Catalysts from Rice Husk by Different Methods for CO₂ Methanation

Silicon dioxide (SiO₂) from rice husk can be extracted and be used as support for Ni-based catalysts. The impregnation method (IM) is usually used for preparing Ni/SiO₂ catalysts, but its catalytic activity in CO₂ hydrogenation to CH₄ remains unsatisfactory. In this work, we explored alternative preparation methods, using ammonia evaporation method (AEM) and hydrothermal method (HM) to prepare the catalysts. The results showed that the catalysts prepared by AEM and HM were significantly superior to that prepared by IM. Notably, the catalyst synthesized by AEM from sustainable silica exhibited the best performance, achieving 81.69 % CO₂ conversion and over 99 % methane selectivity at low reaction temperature of 300 °C. The characterization techniques indicate that the Ni/SiO₂-AEM catalyst can form nickel phyllosilicate with lamellar structure, leading to better Ni dispersion and higher specific surface area. Furthermore, the results of in-situ DRIFTS have revealed the potential catalytic mechanism over Ni/SiO₂ catalysts, indicating that it involves pathways with both the CO* and HCOO* as the key intermediates.