THE STRIKING DIFFERENCE IN THE BEHAVIOR OF RH AND PT TOWARDS THEIR INTERACTION WITH CO(2)

The interaction of CO2 With both Rh and Pt was studied between 80 and 1200 K using field emission microscopy (FEM) and thermal desorption sp ectroscopy (TDS). On Rh the sticking probability at 80 K is high. Diss ociation of CO2 into CO and O starts around 165 K on (210). The influe nce of the surface structure on the dissociation is large. Starting wi th a low initial CO2 coverage, CO recombines with 0 and desorbs as CO2 between 300 and 340 K. At high initial CO2 coverages, some O is force d to diffuse into the bulk. Using a newly developed digital FEM set-up it could be shown that oxygen diffuses out of the bulk between 600 an d 1200 K. Also CO desorption around 450 K was found. CO2 is only weakl y adsorbed on Pt at 80 K with an estimated heat of adsorption of at mo st 25 kJ/mol. No dissociation was found on Pt surfaces. CO2 desorbs ar ound 90 K leaving a clean surface. The surface structure dependence of the adsorption of CO2 on Pt and of the adsorption and dissociation of CO2 on Rh will be discussed.