Consecutive Reduction of Five Carbon Dioxide Molecules by Gas-Phase Niobium Carbide Cluster Anions Nb 3 C 4 - : Unusual Mechanism for Enhanced Reactivity by the Carbon Ligands.

Studying the cleavage of the C═O bond during CO ₂ activation at room temperature is highly significant for comprehending the CO ₂ conversion processes. Herein, mass spectrometry experiments and density functional theory calculations indicate that the niobium carbide anions Nb ₃ C ₄ ^- can continuously convert five CO ₂ molecules to CO under thermal collision conditions, while the other clusters with less carbon ligands Nb ₃ C _1-3 ^- reduce fewer CO ₂ molecules. Size-dependent reactivity of Nb ₃ C _1-4 ^- cluster anions toward CO ₂ is observed. Interestingly, the carbon atoms in Nb ₃ C ₄ ^- not only act as highly active adsorption sites for CO ₂ but also serve as electron donors to reduce CO ₂ . The stored electrons are released through a carbon-carbon coupling process. Our findings on the role of carbon ligands in enhancing transition metal carbide reactivity can offer new insights for designing active sites on catalysts with both high activity and selectivity.