Catalytic Activity of Tandem Catalysts Based on ZnGa2O4 and MFI Zeolite in CO2 Hydrogenation

A series of tandem catalysts based on a ZnGa2O4 spinel and on MFI-type acidic components with varying SiO2/Al2O3 ratios were prepared by mechanical mixing at a spinel to MFI weight ratio of 2 : 1. These catalysts were tested in the conversion of carbon dioxide to olefins at 380 degrees C and 27 bar. The hydrogenating component (ZnGa2O4) was prepared by co-precipitation of the corresponding hydroxides followed by heat treatment. The zeolites were synthesized by steam-assisted crystallization. A reference catalyst was prepared from ZnGa2O4 and a hydrothermally synthesized commercial zeolite CBV28014. The physicochemical properties of the catalysts and their components were characterized by low-temperature nitrogen adsorption-desorption, chemical analysis, NH3-TPD, H-2-TPR, XRD, and SEM. The sample with the highest SiO2/Al2O3 ratio (250) achieved the highest CO2 conversion; this parameter dropped as the aluminum content in the samples increased. The highest selectivity towards light olefins was observed for the catalyst with SiO2/Al2O3 = 172 in the acidic component, likely because this zeolite had an optimum acidity for the production of light olefins.