Impact of the K and Fe insertion methods in KFeCeZr catalysts on the CO2 hydrogenation to C2/C3 olefins at room pressure

Abstract

Light olefins, traditionally sourced from petroleum, are currently being investigated through alternative routes, such as CO₂ hydrogenation, aligning with CCUS policies. Alkali-promoted Fe-based catalysts have shown promise in coupling reverse water–gas shift and Fischer-Tropsch processes to produce light olefins from CO₂ directly. The in-situ generated Fe₅C₂ phase is commonly associated with the high activity of these catalysts. However, the preparation methods employed can lead to distinct catalyst properties, which considerably impact the performance during the reaction. Here, we investigate different strategies to introduce K and Fe in the KFeCeZr system and correlate catalyst properties with catalytic activity during CO₂ hydrogenation at ambient pressure. The catalyst prepared by one-pot precipitation of Fe, Ce, and Zr followed by K impregnation showed the most promising results in terms of conversion and productivity of light olefins. The effective incorporation of Fe in the CeZrO_x structure during synthesis was essential for maintaining the high dispersion of metallic Fe particles after reduction, improving reactant chemisorption. Under reaction conditions, this catalyst showed the most remarkable propensity to form iron carbides (Fe_xC_y), mainly composed of Fe₅C₂ phase. In general, this work highlights the impact that the construction steps of a multifunctional catalyst have on the physicochemical properties and, consequently, on the catalytic activity.