The catalytic reduction of NO by hydrogen is investigated at T = 650 K and p approximate to 10(-6) mbar on a microstructured Rh/Pt(100) surface consisting of Pt(100) domains surrounded by a 600 Angstrom thick Ph film. Synchrotron radiation scanning photoemission microscopy (SPEM), using photons focused into a spot of less than 0.2 mu m diameter, is employed as a spatially and chemically resolving in situ technique. The chemical waves which arise in the bistable system NO + H-2/Rh are imaged with SPEM monitoring the N ls and O ls photoelectrons. The reaction fronts initiate transitions from an inactive oxygen-covered surface (Theta(O) approximate to 0.25 ML) to a reactive nitrogen-covered surface (Theta(N) approximate to 0.06 ML). At the Pt/Ph interface, synergetic effects can be observed: the chemical waves on the Ph film nucleate preferentially at the Pt/Ph interface. This nucleation is poisoned by carbon contamination on the Pt area but is prevented in the vicinity of the Pt/Ph interface by the adjacent clean Ph film. No segregation of Pt to the surface was observed for the 600 Angstrom thick Ph film.