The striking difference in the behaviour of Rh and Pt towards their interaction with CO 2

Abstract

The interaction of CO 2 with both Rh and Pt was studied between 80 and 1200 K using field emission microscopy (FEM) and thermal desorption spectroscopy (TDS). On Rh the sticking probability at 80 K is high. Dissociation of CO 2 into CO and O starts around 165 K on (210). The influence of the surface structure on the dissociation is large. Starting with a low initial CO 2 coverage, CO recombines with O and desorbs as CO 2 between 300 and 340 K. At high initial CO 2 coverages, some O is forced 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 and 1200 K. Also CO desorption around 450 K was found. CO 2 is only weakly adsorbed on Pt at 80 K with an estimated heat of adsorption of at most 25 kJ mol . No dissociation was found on Pt surfaces. CO 2 desorbs around 90 K leaving a clean surface. The surface structure dependence of the adsorption of CO 2 on Pt and of the adsorption and dissociation of CO 2 on Rh will be discussed.