Small platinum clusters are readily generated by electron ionization of Pt-4(PF3)(8) in an FT-ICR mass spectrometer. Pt-n(+) (n = 1-4), cluster ions of a given n value may then be isolated and reacted with a variety of gaseous saturated and aromatic cyclic hydrocarbons. The present experiments thus illuminate catalytic dehydrogenation behavior intermediate between that of single-atom and bulk platinum. Extensive chemisorption (dehydrogenation of the hydrocarbon) and physisorption (nondissociative adsorption of intact neutral reagent molecule on the cluster) occur, depending on the particular reagent species. For example, each of the clusters exhibits chemisorption with at least one Ligand for every neutral reactant species except for hexafluorobenzene. In general, the extent of chemisorption increases with cluster size. Also, some of the reactions do not proceed by a previously proposed C-H bond insertion mechanism. The detailed reaction pathways and product relative yields depend on the metal cluster ion, the reagent neutral species, and the stability of the final product.