Green methanol fuel production by CO2 conversion over Cr2O3-based Al2O3-promoted Cu-ZnO catalysts

Precipitation method was employed to synthesize catalysts featuring Cu-ZnO on Cr2O3 support. Aluminum oxide (AI2O3) was incorporated in varying amounts to investigate its role as a promoter. Various analytical techniques assessed the physicochemical characteristics of calcined catalysts. X-ray diffraction suggested a highly effective distribution of Cu and Zn metal oxides upon the Cr2O3 surface, also verifying the crystalline quality of the Cr2O3 catalyst support. BET surface analyses demonstrated the mesoporosity of Al2O3-promoted Cu-ZnO/Cr2O3 catalysts. Furthermore, the incorporation of Al2O3 improved the BET surface area of the catalysts. X-ray photoelectron spectroscopy (XPS) application uncovered the surface chemistry of Al2O3-promoted Cu-ZnO/Cr2O3 catalysts, advocating highly dispersed form of catalysts components. Temperature program desorption of ammonia (TPD-NH3) studies revealed the enrichment of acidic profile of Cu-ZnO/Cr2O3 catalysts by Al2O3 incorporation. Activity results indicated that Al2O3-promoted Cu-ZnO/Cr2O3 catalysts exhibited efficiency in CO2 hydrogenation to methanol in a liquid-phase slurry reactor. The introduction of Al2O3 to the parent Cu-ZnO/Cr2O3 catalyst enhanced the methanol synthesis rate. The same trend in methanol synthesis rate was continued with further Al2O3 promotion until maximum methanol synthesis rate with magnitude of 19 g.MeOH/kg.cat.h was observed with maximum Al2O3 content. The distribution of catalyst components, improved acidic profile and the increased BET surface area due to aluminum oxide promotion are pivotal in determining the kinetics and selectivity of methanol synthesis, as evidenced by structure-activity analyses. The comparative studies of the current catalysts with other slurry phase methanol synthesis catalysts also advocated the significance of the work.