Tailoring acid-base properties on metal-free zeolite from Indonesia kaolin to enhance the CO₂ hydrogenation to CH₄

The catalytic thermal conversion of carbon dioxide is essential for carbon capture, storage, and utilization, helping to reduce CO₂ emissions and potentially stimulating future economic activities. Zeolite Y, ZSM-5, BEA, and A were synthesized using the hydrothermal technique from Indonesian kaolin to examine the potential use of zeolite as a catalyst without metal nanoparticles. In the absence of metal, catalytic activity for CO₂ methanation relies solely on textural properties and basicity-acidity. Zeolite Y exhibits the highest CO₂ conversion at 36.64 % and attained 100 % of CH₄ selectivity at 400 °C. The exceptional CO₂ conversion of zeolite Y relies on a high basicity level of 1.02 mmol/g, as shown by CO₂-TPD analysis, and a relatively low acid site concentration of 1.48 mmol/g, as determined by NH₃-TPD analysis. ZSM-5, BEA, and zeolite A, demonstrated CO₂ conversion of 29.85 %, 23.86 %, and 12.15 %, respectively. Stability studies revealed ZSM-5 maintains methane (CH₄) selectivity of 94 %, which is only slightly lowered by 6 % for 30 hours, while zeolite Y achieved 90 % selectivity for 26 hours. The presence of mesopores in zeolite ZSM-5 reduced coke or carbon production, maintaining crystalline framework.