Cs-Induced Modulation of FeO x /FeC x Interfacial Environments for Selective CO2 Hydrogenation to Olefins on Iron-Based Catalysts

Abstract The selective conversion of CO2 into valuable C2+ olefins and higher hydrocarbons offers a cost-effective route to reduce fossil fuel dependence but remains a grand challenge in heterogeneous catalysis due to competing methanation and over-hydrogenation pathways. Here, we elucidate the role of highly electropositive cesium in tuning Fe-based catalysts for CO2 hydrogenation. Systematic variation of Cs/Fe ratios, coupled with XRD, Mössbauer spectroscopy, XPS, spatially resolved ELNES, in situ DRIFTS-MS, steady-state kinetics, and transient isotopic-labeling studies, revealed that Cs-containing species modify the FeOx/FeCx ensembles and shift the rate-limiting step in the coupled RWGS-FTS reaction network. At high Cs loadings (Cs/Fe = 0.2), catalysts achieve stable performance with ∼50% selectivity to C2=−C4= olefins and ∼29% to C5+ hydrocarbons, while suppressing methane formation. Operando studies and temperature-programmed reaction show that Cs enriches surface carbides, moderates H2 activation, and stabilizes CHx intermediates, thereby redirecting hydrocarbon selectivity toward olefins and heavier hydrocarbons. These findings provide molecular-level insights into alkali promotion, highlighting Cs as an electronic modulator and a geometric spacer of Fe active sites. More broadly, this work establishes alkali-induced modifications of FeOx/FeCx interfacial environment and the RWGS-FTS kinetic balance as control activity and selectivity in CO2-FTS to high-value chemicals and fuels.