Spatial variations of the interface composition during surface chemical reactions

The spatial distribution of potassium under reaction conditions on a compos ite Pt/Rh catalyst has been studied employing photoelectron spectromicrosco py as in situ method during the H-2 + O-2 reaction. The composite catalyst consisted of a 70X70 mum(2) Pt domain on a Rh(110) surface predosed with a submonolayer coverage of potassium. This catalyst. was er;posed to an O-2 H-2 atmosphere in the 10(-7) mbar range. The combination of chemical speci fic imaging with a spatial resolution of 0.12 mum and micro-spot spectrosco py provided direct evidence for lateral re-distribution of potassium into a stationary concentration pattern under reaction conditions. The identity o f the adsorbed species in the pattern and the changes in the chemical state of the substrate were determined. (C) 2001 Elsevier Science B.V. All right s reserved.