Abstract
CO oxidation was studied on Pd-rich surfaces of a PdCu (110) single crystal alloy. The top layer contained initially ~100% Pd atoms. The techniques used were Auger electron spectroscopy, low energy electron diffraction and thermal desorption spectroscopy. The experiments were performed at constant CO and O 2 pressures while varying the temperature of the sample up to 575 K. Measurement of the rate of CO 2 production versus the temperature enabled the detection of regions of bistability and hystereses to be recorded. AES, with surface region analysis of ~ 4 layers, enabled the recording of an increase in the Cu Pd ratio from ⩽ 0.1 to ~ 0.7 after CO-oxidation experiments. This occurred due to the segregation of Cu from the bulk mostly into the three subsurface layers beneath the top layer. For this reason the type of lattice changed from fcc to bcc in the surface region. The (1 × 1) clean surface structure changed to c(2 × 2) after being exposed to intensive CO-oxidation treatment. Recording the CO- TDS after each measurement provided valuable information about the mechanism which controls the adsorption and desorption on the surface. The relative CO coverage versus the doses of CO demonstrated that after each CO-oxidation experiment less CO was able to adsorb on the surface. The results together fulfil one of the requirements of a system that could display surface kinetic oscillations.
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