THE ADSORPTION AND DISSOCIATION OF CO2 ON RH

The adsorption and dissociation of CO2 on Rh were studied at temperatu res between 80 and 1200 K with field emission microscopy. For this pur pose a new microscope was used which is based on image processing. Thi s DigiFEM has a very high spatial resolution. Because of this high res olution the surface structure specificity of adsorption and dissociati on could be monitored in detail. CO2 adsorption at 80 K starts on (210 ) followed by adsorption on (1 10), (321), (221), (511)-(711) and (310 ). At low surface coverages CO2 dissociation starts around 165 K on (2 10). A little below this temperature also CO2 rearrangement over the s urface and some CO2 desorption take place. Between 235 and 290 K CO re combines with O to form CO2 which desorbs leaving a clean surface at 3 40 K. At higher coverages two processes take place simultaneously. Fol lowing CO2 desorption around 120 K, CO2 dissociation starts around 190 K. Some CO2 is desorbed after recombination of CO with O, but CO2 dis sociation 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 diffus e out of the bulk around 600 K. These O-atoms are desorbed as O2 or Rh O(x) between 1000 and 1200 K. In order to solve the processes taking p lace during the study of the interaction of CO2 with Rh the results ob tained were compared with results obtained for the adsorption and deso rption of CO and O2 on the same tip.