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 Niδ+-O-Feδ+ in NiFe-350/TiO2, the dual-site synergy of which enhances CO2 activation and facilitates H2 heterolytic activation into Hδ- 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.