Аннотация:The article examines consistent mathematical micro- and macro-level models of CO oxidation on platinum-group metals. New mechanisms responsible for the excitation of oscillations are studied in detail by simulation. Micro-level oscillations may arise in parameter-space regions where the corresponding macro model has a limiting cycle, a bistability, or a unique stable steady-state solution. In the latter case, necessary conditions for the excitation of oscillations include fluctuations in the concentration of adsorbed particles, which are characteristic of micro models of small-volume systems, and a special arrangement of the macro-model trajectories on the phase plane producing sensitivity to small perturbations or excitability of the medium.