The effect of well-defined palladium boundaries on the formation of reaction-diffusion patterns during the oxidation of CO on Pt(1 1 0) has been investigated. The Pd boundaries were created by microlithography technique. Reaction-diffusion patterns formed on this surface were observed by photoemission electron microscopy (PEEM). On a multilayer Pd-covered Pt(1 1 0) surface, depending on the partial pressures, Pd areas may act as a reservoir of CO for adjacent Pt regions. Therefore, patterns forming on the bare Pt areas exhibit a pronounced interaction with the artificial Pt/Pd boundaries. Copyright (C) 1998 Elsevier Science B.V.