Efficient Promoters and Reaction Paths in the CO₂Hydrogenation to Light Olefins over Zirconia-Supported Iron Catalysts

Abstract

Hydrogenation into light olefins is an attractive strategy for CO₂fixation 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 CO₂hydrogenation 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 CO₂hydrogenation 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 CO₂conversion, 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 CO₂conversion. 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.