The surface structure and catalytic properties of model silica-supported nickel catalysts have been investigated with infrared reflection-absorption spectroscopy (IRAS) and reaction kinetics of ethane hydrogenolysis and carbon monoxide methanation. Nickel particles in the range 15-80 Angstrom were vacuum deposited onto silica thin films using established preparation procedures. Specific rates and activation energies for ethane hydrogenolysis and carbon monoxide methanation over the model catalysts are remarkbly similar to the corresponding values for both traditional silica-supported nickel catalysts and nickel single crystals. The turnover frequency for CO methanation is independent of particle size for the dimensions studied. The ethane hydrolysis rate, however, increases with particle size to a maximum at similar to 25 Angstrom and then decreases. This reactivity trend is found to parallel a change in the percentage of bridging CO on the nickel particles as determined by IRAS.