Rate oscillations during heterogeneous catalytic reactions often display self-similar mixed-mode oscillations that have also been found in various other experimental systems. Spatially nonuniform behavior is revealed by monitoring the surface temperature during complex oscillations in the kinetic regime of the CO oxidation on a Pd supported catalyst at atmospheric pressure. The experimental results demonstrate the influence of global coupling via the gas phase concentration of the deficient component. In addition, the local autonomous frequency appears to be spatially nonuniform. A simple discrete model, a set of globally coupled relaxation oscillators with a frequency distribution, captures qualitatively the experimentally observed behavior.