The impact of surface size on two minimalistic models for the bistable CO oxidation is
analytically studied. A simple model for the catalytic CO oxidation on nanoscale surfaces
is analyzed by the chemical master equation. The analytical results predict a shift of the
bistable region and cusp point in the global bifurcation diagram as a function of surface
size. A reaction diffusion stochastic model consisting of a collection of reactive subdomains
locally coupled by CO diffusion is also considered. A local description of fluctuations can be obtained after applying a Weiss-type mean-field approximation. This approximation predicts, for infinitely many subdomains, a break of ergodicity and a bifurcation behavior like in first-order phase transitions as a function of surface size and coupling parameter. Analytical results are compared with Gillespie-type Monte Carlo simulations.