Green synthesis approach for preparing zeolite based Co-Cu bimetallic catalysts for low temperature CO₂ hydrogenation to methanol

In this study, zeolite based Cu-Co bimetallic catalysts were synthesized by green deposition precipitation method. To investigate the optimum metal-metal ratio, catalysts with different Cu-Co metal weight ratios were evaluated for CO₂ hydrogenation to methanol. The XRD analysis revealed crystalline nature of zeolite support with deposition of highly dispersed Cu-Co metal oxides. The FESEM observation showed well dispersed morphology of zeolite based Cu-Co bimetallic catalysts. The nitrogen adsorption-desorption studies showed that surface area of Cu-Co bimetallic catalysts was slightly decreased by increasing Cu content in bimetallic catalysts. Temperature program reduction studies exhibited synergism between the Cu-Co metals which resulted variation in reduction behavior of zeolite based Cu-Co bimetallic catalysts. Similarly, XPS studies revealed metal-metal interaction by shifting XPS peaks to higher binding energies regions. Temperature program desorption investigations showed the existence of three types of basic sites on the surface of zeolite based Cu-Co bimetallic catalysts. Activity profiles of zeolite based Cu-Co bimetallic catalysts were examined for low temperature CO₂ hydrogenation to methanol in slurry reactor. The activity studies documented enhancement in methanol synthesis rate from 7.5 to 25.6 g/Kg_cat.h by increasing the Cu content in catalysts. Based on the physico-chemicals findings and activity data, structure-activity patterns were elaborated in details.