In order to aid in the search for fundamental understanding of the particle size effect in catalysis, a model system has been developed. The system consists of Pt vapor deposited onto the basal plane of highly oriented pyrolytic graphite, HOPG(bp). The electronic structure of Pt/HOPG(bp) has been probed with X-ray photoemission spectroscopy. It was found that there is a small decrease in the Pt 4f binding energy with Pt coverage (∼0.1eV in going from a 1% to a 50% monolayer coverage surface). There is a further decrease in binding energy of ∼0.1eV after the surface has been heated to ∼1000K. The morphology of the Pt islands has been studied with an ambient scanning tunneling microscope, STM. STM shows that Pt deposited on a 300K HOPG(bp) surface forms islands that are ∼5nm across and ∼0.4nm high. The height of the islands is insensitive to the Pt coverage between 1% and 50% of a monolayer. Heating the surface causes the island height to increase by a factor between 5 and 10 times. The gas phase chemical behavior of Pt/HOPG(bp) has been probed with temperature programmed desorption, TPD, using O₂ and CO as adsorbates. The O₂ TPD peak increases in temperature by ∼25K when the Pt/HOPG(bp) surface is pre-heated to ∼1000K. The CO spectra show a broad series of pea ks whose population shifts from the high temperature end to the low temperature end when the Pt/HOPG(bp) surface is pre-heated. Preliminary studies of the liquid phase chemical behavior of Pt/HOPG(bp) have been performed using both an in-situ and an ex-situ electrochemical cell. The in-situ work shows that an 80% Pt/HOPG(bp) surface displays a cyclic voltammogram in 0.1M KOH very similar to bulk Pt. A 5% Pt/HOPG(bp) surface was found to display stable behavior upon potential cycling in 0.1M KOH. The voltammogram had some but not all of the bulk Pt characteristics. The ex-situ work shows that 10% Pt/HOPG(bp) is capable of catalyzing CO oxidation. In addition, titration of the CO oxidation peak yields an active site density equal to one half the Pt coverage estimate by XPS.