A mathematical model is formulated to account for experimental infrared thermography observations of spatiotemporal patterns during catalytic oxidation of CO over Pd supported on a glass-fiber disk-shaped cloth in a continuous reactor with feed flowing perpendicular to and through the disk. The model predicts the following observed features: (a) The sustained pattern that the system exhibits is a breathing motion in which a hot spot expands and contracts continuously. This motion emerges due to the imposed cold-edge boundary condition and a qualitative analysis of the experiments supports this suggestion and rules out other mechanisms. (b) The emerging temporally complex patterns can be classified as mixed-mode oscillations with a large relaxation-type conversion peak superimposed with several smaller peaks. (c) The mathematical mechanism that accounts for the change in the number of smaller peaks with varying operating conditions (the reactor temperature) could be characterized as period adding. The mathematical model is based on a published oscillatory kinetics model, and is coupled here with an enthalpy and gas-phase balances with two adjusted parameters. Numerical simulations map the simple and the complex oscillations domains and characterizes the transition between them as either period doubling or period adding. (C) 2003 American Institute of Physics.