Elucidating the promoting role of Ca on PdZn/CeO₂ catalyst for CO₂ valorization to methanol

The viability of catalyzed CO₂ conversion routes strongly depends on improving the catalytic performance and understanding of the process. Herein, we investigate the effect of Ca loading on PdZn/CeO₂ catalysts prepared using the sol–gel chelatization method for CO₂ hydrogenation to methanol. A remarkable improvement in catalyst performance was revealed with the optimum amount of Ca (0.5 wt%) in synergetic cooperation with the PdZn alloy (main active phase for the CO₂ hydrogenation to methanol reaction), compared to the Ca-free counterpart. The following key performance indicators are attained at 230 °C, 20 bar, and 2400 h⁻¹ GHSV for the optimized catalyst: 16 % CO₂ conversion, > 93 % methanol selectivity, and ∼ 124 g/kg_cat/h methanol space–time yield. The overall catalytic performance observed is attributed to the optimum Ce³⁺/Ce⁴⁺ ratio, Ca²⁺ promotion, surface area, pore volume, and basic sites, as revealed by various characterization techniques. Results shown here indicate that the presence of Ca in the vicinity of the PdZn active enhances basicity, creates oxygen vacancies, and phase may have improved the spill-over ability of H₂, consequently favoring CO₂ activation and methanol formation.