Abstract
The present study investigates the effect of Ni and Mg oxide incorporation methods into Li₄SiO₄ synthesized from natural zeolite of the Taizhuzgen deposit on the structure and catalytic performance in CO₂ methanation. Ni/Li₄SiO₄, Ni-Mg/Li₄SiO₄ prepared by capillary impregnation (CI), and Ni-Mg/Li₄SiO₄ synthesized via solution combustion (SC) at a Li: Si ratio of 1.5:1 were evaluated in the CO₂ + 4 H₂ → CH₄ + 2 H₂O reaction at 250-550 °C. XRD, SEM-EDS, H₂-TPR, CO₂-TPD, XPS, TEM/HRTEM, and TGA analyses revealed correlations between phase composition, reducibility of Ni species, basicity, and catalytic behavior. Li₄SiO₄ formed predominantly as orthosilicate (~ 93 wt%) and acted as an effective support for Ni and Ni-Mg catalysts. The Ni-Mg/Li₄SiO₄ (CI) catalyst, characterized by uniformly dispersed Ni particles and balanced medium and strong basic sites, achieved 75-78% CO₂ conversion and 87-88% CH₄ selectivity at 450-500 °C. In contrast, the more porous Ni-Mg/Li₄SiO₄ (SC) catalyst with predominantly strong basic sites reached complete CO₂ conversion but showed lower CH₄ selectivity (20-50%) due to enhancement of the RWGS pathway. Stability tests showed higher coke formation for the Ni-Mg/Li₄SiO₄ (CI) catalyst, whereas the Ni-Mg/Li₄SiO₄ (SC) catalyst exhibited lower carbon deposition and greater stability.