High-pressure switch: Redirecting CO2 hydrogenation from hydrocarbons to carboxylic acids and alcohols

Abstract

The selective conversion of CO₂ into value-added chemicals remains a critical challenge in heterogeneous catalysis. Here, we demonstrate that reaction pressure governs a decisive mechanistic switch in CO₂ hydrogenation over potassium-promoted iron catalysts. Catalytic tests conducted from 0.1 to 10.0 MPa reveal that moderate pressure (3.5 MPa) favors Fischer-Tropsch-type pathways, yielding long-chain hydrocarbons through Fe₅C₂-mediated C–C coupling. In contrast, elevated pressures (≥ 7.0 MPa) suppress hydrocarbon formation and promotes the production of long-chain oxygenates, including higher alcohols and carboxylic acids. Comprehensive structural characterization indicates a clear pressure-dependent phase transformation: Fe₅C₂ progressively diminishes and evolves into FeCO₃, accompanied by increased Fe–O and carbonate surface species. Operando diffuse reflectance infrared Fourier transform spectroscopy reveals that FeCO₃-rich surfaces stabilize COO-containing intermediates and inhibit C–O bond scission, favoring direct COO insertion rather than Fischer-Tropsch chain growth. CO-temperature programmed surface reaction further confirms that FeCO₃ is catalytically inert toward CO activation, explaining the reduced CO₂ conversion observed at high pressure. The combined results establish FeCO₃ as a pressure-generated phase that redirects CO₂ hydrogenation from hydrocarbon-selective to oxygenate-selective pathways. This work provides mechanistic insight into pressure-driven catalyst restructuring and offers a new strategy for tuning oxygenate selectivity in CO₂ hydrogenation.