Efficient Promoters and Reaction Paths in the CO₂ Hydrogenation to Light Olefins over Zirconia-Supported Iron Catalysts

Hydrogenation into light olefins is an attractive strategy for CO2 fixation into chemicals. In this article, high throughput experimentation and extended characterization were employed to identify the most efficient promoters and to elucidate structure-performance correlations and reaction paths in the CO2 hydrogenation to light olefins over zirconia-supported iron catalysts. K, Cs, Ba, Ce, Nb, Mo, Mn, Cu, Zn, Ga, In, Sn, Sb, Bi, and V were added in the same molar concentrations to zirconia-supported iron catalyst and evaluated as promoters. The CO2 hydrogenation proceeds via intermediate formation of CO followed by surface polymerization. Over the iron catalysts containing alkaline promoters, initially higher selectivity to light olefins shows a significant decrease with the CO2 conversion, because of further surface polymerization and the formation of longer chain hydrocarbons. A relatively low selectivity to light olefins over the promoted catalysts, without potassium, is not much affected by the CO2 conversion. Essential characteristics of iron catalysts to obtain a higher yield of light olefins seem to be a higher iron dispersion, a higher extent of carbidization, and optimized basicity. The strongest promoting effect is reported for the alkaline metals. A further increase in the light olefin selectivity is observed after simultaneous addition of potassium with copper, molybdenum, gallium, or cerium.