DEHYDROGENATION OF XYLENE ISOMERS ON NIOBIUM CLUSTER CATIONS NB-N(-26)() (N=2)

The dehydrogenation of the mono-, di-, and trimethyl-substituted benze nes (toluene, o-, m-, p-xylene, and mesitylene) on niobium cluster cat ions Nb-n(+), n = 2,..., 26, in the gas phase was investigated in an F T-ICR mass spectrometer. While most Nb-n(+) clusters dehydrogenate the compounds completely, a partial dehydrogenation is observed for very small clusters with n less than or equal to 6 and clusters in the rang e 15 less than or equal to n less than or equal to 19. Selectively deu terated xylenes are used to clarify the mechanisms of the isomer speci fic dehydrogenation reactions, and the observed results and trends are discussed.