Pt nanoparticle array model catalysts with 28+/-2 nm diameters and 100+/-2 nm interparticle spacing have been fabricated with electron beam. lithography on alumina supports. A novel method for cleaning the Pt nanoparticle arrays, involving low dosages of NO2 and CO and mild temperature flashing, was established. This cleaning procedure was crucial for measuring reaction rates over the nanoparticle arrays. The reactivity of the Pt/Al2O3 arrays was compared to a Pt(111) single crystal for the ethylene hydrogenation reaction. The activation energy and the pressure dependence of the H-2, and C2H4 on the nanoparticle array were in excellent agreement with the kinetic data on the Pt(111) single-crystal model catalyst. Because the ethylene hydrogenation reaction is structure insensitive, the rate equation for Pt(111) can be applied to the Pt nanoparticle arrays. The calculated turnover frequency led to a calculated active metal surface area that compared very well with an active metal surface area on the basis of geometry. This reaction can therefore be used to determine the active metal surface area of the Pt nanoparticle array model catalysts. The arrays were characterized with AFM, SEM, XPS, and AES before and after being exposed to reaction conditions.