Cs-Induced Modulation of FeO _<i>x</i> /FeC _<i>x</i> Interfacial Environments for Selective CO ₂ Hydrogenation to Olefins on Iron-Based Catalysts

The selective conversion of CO 2 into valuable C 2+ 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 CO 2 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 FeO x /FeC x 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 C 2 =−C 4 = olefins and ∼29% to C 5+ hydrocarbons, while suppressing methane formation. Operando studies and temperature-programmed reaction show that Cs enriches surface carbides, moderates H 2 activation, and stabilizes CH x 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 FeO x /FeC x interfacial environment and the RWGS-FTS kinetic balance as control activity and selectivity in CO 2 -FTS to high-value chemicals and fuels.