Comparative study of the impact of Al2O3, ZrO2, and CeO2 promoters on the structural and catalytic performance of Cu-ZnO catalysts for CO2 hydrogenation to methanol

This study compares the impact of Al 2 O 3 , ZrO 2 , and CeO 2 promoters on the morphology and catalytic activity of Cu-ZnO catalysts for CO 2 hydrogenation to methanol. The catalysts were prepared via co-precipitation under identical conditions. XRD analysis revealed that ZrO 2 and CeO 2 inhibit CuO crystallization, resulting in smaller CuO nanoparticles in the Cu-ZnO-ZrO 2 (CZZ) and Cu-ZnO-ZrO 2 -CeO 2 (CZZC) catalysts compared to the baseline Cu-ZnO-Al 2 O 3 (CZA) catalyst, wherein Al 2 O 3 promotes CuO crystallization. According to the TPR analysis, enhanced reducibility of CuO particles was observed with ZrO 2 and CeO 2 additions, facilitating more active Cu species for CO 2 hydrogenation. The results of the reaction tests at 250 ℃, H 2 /CO 2 = 3/1, GHSV = 5700 NmL·g -1 ·h -1 , and P = 4.5 MPa, proved that ZrO 2 is a more effective promoter than Al 2 O 3 or CeO 2 for enhancing CO 2 conversion and methanol yield. Crucially, this systematic study under unified conditions reveals that adding a secondary promoter (Al 2 O 3 or CeO 2 ) to a high-performing ZrO 2 -containing catalyst offers minimal to no improvement, with the ZrO 2 -Al 2 O 3 combination even exhibiting an antagonistic effect. CZZC demonstrated a high CO 2 conversion (28.7 %) with the highest yield for CO 2 hydrogenation to methanol, achieving 12.74 %, along with the greatest methanol selectivity of 44.3 % among all tested catalysts. This represents a remarkable improvement of approximately 18 % in CO 2 conversion, 57 % in methanol yield, and 33 % in methanol selectivity compared to the CZA catalyst.