Ambient-Pressure C-C Coupling of CO₂ Hydrogenation by NiFe/TiO₂ Bimetallic Catalyst

Catalytic upgrading of CO₂ to value-added C₂₊ products offers promising solutions to trim carbon emissions with additional economic benefits. Herein, we report a NiFe bimetallic catalyst showing efficient ambient-pressure C-C coupling performance subject to H₂ pretreatment temperature. An optimal performance was achieved after reducing NiFe/TiO₂ at 350 °C (NiFe-350/TiO₂), yielding 27.8% CO₂ conversion and 33.9% selectivity to C₂-C₃ hydrocarbon (primarily ethane) at 350 °C under atmospheric pressure. Combinatorial studies employing in situ characterizations, kinetic, intermediate control experiments and first-principles calculations indicate the formation of partially oxidized Ni^δ+-O-Fe^δ+ in NiFe-350/TiO₂, the dual-site synergy of which enhances CO₂ activation and facilitates H₂ heterolytic activation into H^δ- species that selectively hydrogenate *CO₂ into HCOO* and *CH₃O intermediates, thus suppressing CO byproduct formation and resulting in effective ambient-pressure C-C coupling likely via an asymmetric *CH₂-CH₃ coupling mechanism. In stark contrast, the fully reduced NiFe bimetallic catalyst favors a direct CO₂ dissociation pathway instead to form *CO that easily desorbs from the surface, as well as homolytic H₂ activation such that the C-C coupling process is unfavored. In brief, this work reports the ambient-pressure synthesis of C₂-C₃ paraffins from direct CO₂ hydrogenation and provides design rationales for efficient carbon chain propagation.