Turning methanation into chain growth: Na-induced mechanistic bifurcation on Co-ZrO_x catalyst

Direct hydrogenation of CO₂ to long-chain hydrocarbons represents a promising route for carbon-neutral fuel production, yet achieving high selectivity and catalyst stability remains a formidable challenge. In this study, we systematically investigate the promotional effect of alkali metals (Li, Na, K) on cobalt-zirconia catalysts, revealing that the nature of the alkali promoter governs both redox stability and product distribution. While unpromoted and K-promoted catalysts undergo extensive surface reoxidation during CO₂ hydrogenation, suppressing C–C coupling and favoring methane formation, the Na-promoted catalyst preserves the metallic Co0 phase and achieves exceptional C₅₊ hydrocarbon selectivity (39.4%) and yield (22.4%) under industrially relevant conditions. Mechanistic investigations reveal that Na uniquely facilitates the formation of hydroxyl and formyl intermediates conducive to C–C bond formation, while avoiding carbonate passivation observed in the Li-promoted catalyst. This work highlights a previously unrecognized role of Na in simultaneously stabilizing active sites and directing reaction pathways, offering a rational strategy for designing robust, selective cobalt-based catalysts for CO₂ conversion to liquid hydrocarbons that can be used as sustainable transportation fuel.