The adsorption and dissociation of CO 2 on Rh

Abstract

The adsorption and dissociation of CO 2 on Rh were studied at temperatures between 80 and 1200 K with field emission microscopy. For this purpose a new microscope was used which is based on image processing. This DigiFEM has a very high spatial resolution. Because of this high resolution the surface structure specificity of adsorption and dissociation could be monitored in detail. CO 2 adsorption at 80 K starts on (210) followed by adsorption on (110), (321), (221), (551)-(711) and (310). At low surface coverages CO 2 dissociation starts around 165 K on (210). A little below this temperature also CO 2 rearrangement over the surface and some CO 2 desorption take place. Between 235 and 290 K CO recombines with O to form CO 2 which desorbs leaving a clean surface at 340 K. At higher coverages two processes take place simultaneously. Following CO 2 desorption around 120 K, CO 2 dissociation starts around 190 K. Some CO 2 is desorbed after recombination of CO with O, but CO 2 dissociation continues to be of importance. Oxygen formed at these higher temperatures and coverages is forced to diffuse into the bulk of Rh. CO desorption takes place with T max=450 K. O-atoms start to diffuse out of the bulk around 600 K. These O-atoms are desorbed as O 2 or RhO x between 1000 and 1200 K. In order to solve the processes taking place during the study of the interaction of CO 2 with Rh the results obtained were compared with results obtained for the adsorption of CO and O 2 on the same tip.