The dehydrogenation of perdeuterated cyclohexane and benzene on Pt/ZnO(0001)-O model catalysts were studied with temperature programmed desorption (TPD), ion scattering spectroscopy (ISS), and X-ray photoelectron spectroscopy (XPS). Pt grows as 2-dimensional (2D) islands on ZnO(0001)-O until they cover ~50% of the surface, and then 3D islands form. Thus, the reactivity of these Pt islands can be studied as a function of their thickness and lateral dimensions. On Pt(111), most of the adsorbed cyclohexane converts to benzene (> 300 K) decomposing to H@sub 2@ and adsorbed carbon. Two H@sub 2@ TPD peaks, at ~360K and ~540 K, are due to desorption of H lost in producing adsorbed benzene and C-H bond scission in benzene, respectively.@footnote 1@ Perdeuterated cyclohexane desorbs molecularly at ~200 K from Pt-free ZnO(0001)-O, and ~240 K from the Pt islands, where decomposition also occurs. The Pt island thickness affects the decomposition reaction of the resulting adsorbed hydrocarbons dramatically. @FootnoteText@ @footnote 1@ J. A. Rodriguez and C. T. Campbell, J. Phys. Chem. 1989, 93, 826-835.