Activation of methane and methane-d4 by ionic platinum clusters

Bimolecular reactions of cationic platinum clusters Ptn+, n = 1–24, and anionic platinum clusters Ptn−, n = 3–22, with CH4 and CD4 are studied under low pressure conditions in an FT-ICR mass spectrometer, using an isotopically enriched 195Pt sample. Strongly size-dependent dehydrogenation and formation of PtnCH2+/− is observed for both charge states. Starting with n = 12, cationic clusters also afford stabilization of a [Ptn, CH4]+ adduct, presumably the HPtnCH3+ insertion compound. Deuteration shifts the lower limit for adduct formation to n = 8. It is suggested that the strong reactivity fluctuations over a wide size range are the gas phase fingerprint of a good heterogeneous catalyst material.