OXYGEN AND CARBON-MONOXIDE INTERACTIONS ON RH(110) STUDIED BY REAR-TIME X-RAY PHOTOEMISSION SPECTROSCOPY

The interaction of CO with a (2 x 1)p2mg oxygen layer on (1 x 1)-Rh(11 0) and a c(2 x 8) oxygen layer on (1 x 4)-Rh(110) has been studied by synchrotron radiation real-time X-ray photoelectron spectroscopy, low energy electron diffraction and mass spectrometry. The structure and c omposition of the surface layer were continuously monitored during the reaction performed at 200, 290 and 350 K. The intensity of the compon ents of the O 1s spectra reflected the changes in the oxygen and CO co verages during the reaction. The intensity decrease of the O 1s peak a t binding energies <530.3 eV, corresponding to the adsorbed oxygen, wa s used as a measure of the CO oxidation rate. The emergence and increa se of a second O 1s peak at binding energies > 531.0 eV identified the CO uptake. The changes in the CO2 partial pressure during titration o f the oxygen layers with CO were also monitored by a mass spectrometer . The observed difference in the reactivity of the (2 x 1)p2mg and c(2 x 8) layers was related to the structural differences of the two surf aces: the (1 x 4) reconstruction creates adsorption sites where oxygen is more strongly bonded and less reactive. The effect of the structur al changes on the reaction rate was observed during the titration reac tion at 350 K. (C) 1997 Elsevier Science B.V.