Methane activation by rhodium cluster argon complexes

Rhodium cluster argon complexes Rh⁺_n Ar_m are produced by laser vaporization followed by supersonic expansion, stored in an FT-ICR mass spectrometer, and their reactions with methane investigated. Ligand exchange reactions are observed, in which up to three argon atoms are replaced by methane. In addition, the solvated rhodium dimer and trimer cations are found to dehydrogenate methane. The efficiency of the dehydrogenation depends on the number of argons, with only the dimer exhibiting this reaction without ligands. This dependence of methane activation on the size of the cluster and number of "solvent" argon atoms is discussed, and compared with heterogenous catalysis on bulk surfaces, where activity and selectivity are controlled by pressure and temperature.