A reaction-diffusion model for CO oxidation on Pt(110) single crystals proposed by Krischer, Eiswirth, and Ertl is supplemented by an equation for the balance of CO partial pressure in the gas phase. This allows us to study the interaction of local and global coupling with the dynamics of the reaction in the oscillatory regime. In absence of global coupling a stability analysis of the homogeneous oscillatory state predicts parameter regions with negative values of the phase diffusion coefficient indicating the possibility of phase turbulence. In the globally coupled system without diffusion we observe the formation of phase-locked clusters of oscillators and irregular behavior. If both surface diffusion and global coupling through the gas phase are taken into account depending on the range of external parameters we get the following types of structures : phase flips, standing waves, spatially irregular coverage pattern, and the uniformly oscillating surface.