A charge-redistribution threshold governing methane dehydrogenation revealed by cerium oxide and nitride clusters

The extent of methane dehydrogenation is ultimately governed by how a catalyst accommodates the charge redistribution accompanying successive C-H bond cleavage. While thermodynamic and structural factors are often invoked to rationalize reactivity trends, the electronic requirement that defines the limit of complete methane dehydrogenation has not been quantitatively established. Here, we investigate the size- and composition-dependent reactivity of mass-selected cerium oxide and nitride cluster cations, Ce_nO_m⁺ and Ce_nN_m⁺ (3 ≤ n ≤ 5), toward methane. By combining ion-molecule reaction experiments with density functional theory calculations, we directly correlate the extent of methane dehydrogenation with the charge-accepting capacity of the cerium centres. For the cerium clusters examined here, complete C-H bond scission requires the cerium centres to accommodate an approximately +1e increase in net positive charge. Methane dehydrogenation terminates at partially hydrogenated intermediates on clusters that are unable to accommodate this degree of charge redistribution. Comparison between oxide and nitride coordination reveals how the nature of Ce-O and Ce-N bonding modulates the charge-accepting capacity of the cerium centres. These results identify charge-accepting capacity as a quantitative electronic criterion governing the methane dehydrogenation limit in cerium-based clusters and suggest its broader relevance to redox-active metal-ligand systems.