Oscillatory states in ammonia oxidation catalyzed by a platinum wire occur around the stoichiometric ratio of the two reactants. The boundary of the oscillatory domain is identified as a soft (Hopf) bifurcation at low temperatures and a hard (global-saddle-node) bifurcation at higher temperatures. We use this information to construct a qualitative model. The oscillatory domain is composed of aperiodic motions interdispersed with bands of multipeak periodic state. Bifurcations in shape of the oscillation occur thorugh one of three routes leading to chaos: period doubling, quasiperiodicity, or intermittency.