RHEED STRUCTURE-ANALYSIS OF THE OSCILLATORY CATALYTIC CO OXIDATION ATPT(110) SURFACES

The catalytic CO oxidation at Pt(110) is observed with RHEED. Due to d ifferential pumping of the electron gun, rocking curves can be measure d up to pressures in the 10(-3) mbar range. This allows, for the first time, structural investigations with atomic resolution under time-dep endent reaction conditions. At very sharply defined values of CO and O pressures at 535 K, the intensities of the diffraction spots oscillat e with a frequency of about 0.6 Hz. These oscillations are associated with a periodic lifting of the (1 x 2) missing-row phase into a disord ered (1 x 1) phase, which takes place spatially homogeneously over the observed part of the surface. A multiple scattering scheme for RHEED intensity calculations is used to evaluate the rocking curves. The cha nges of the substrate structure and the variation of the coverages of several adsorption sites for CO and O are obtained. A simplified Versi on of differential rate equations allows the time-dependent sticking, desorption and reaction of the adsorbates during the oscillations to b e visualized and yields estimates of the relevant rate constants. (C) 1997 Elsevier Science B.V.