MECHANISMS OF THE CO OXIDATION ON THE PD(110)C(2X4)-O SURFACE

The Pd(110)c(2 x 4)-O surface was exposed to various amounts of CO at 90 K, and the reaction-rate-limited CO2 desorption was studied by ther mal desorption spectroscopy (TDS). The results were correlated with th ose of high resolution electron energy loss spectroscopy (EELS) and lo w-energy electron diffraction (LEED). As the temperature is increased (heating rate 4 K s(-1)), the sizes of the c(2 x 4)-O patches become s maller with the remaining O atoms located in the quasi-three-coordinat ed sites until the CO2 desorption is completed. The CO molecules are m obile beyond 200 K. The CO2 desorption occurs as soon as the CO admole cules obtain sufficient translational kinetic energy to approach O ada toms (at the peripheries of the c(2 x 4)-O patches) in close proximity . Three CO2 desorption peaks were observed which are directly correlat ed with three different adsorbed sites of CO. These results are quite different from the CO2 desorptions on Pd(111) and Pd(100) surfaces. Th e CO2 desorptions from CO on other oxygen-covered Pd(110) surfaces, i. e. (2 x 3)-1D, c(2 x 6). ''complex'' and pseudo-(2 x 1), were also bri efly investigated. The CO2 desorption peaks were observed which are co rrelated with unstable O and subsurface O. A CO2 desorption peak was a lso observed which occurs by the direct interaction of O-2 molecules w ith CO on the c(2 x 4)-O surface. (C) 1998 Elsevier Science B.V.