CO OXIDATION ON RH/AL2O3 CATALYSTS

Results of an in situ FTIR study are reported for the reaction of CO and O2 over Rh/Al2O3. Particular attention has been paid to morphology changes occurring during the reaction. At low O2 : CO ratios, agglomeration of dispersed Rh occurs, leading to formation of Rh clusters with linear carbonyl adsorption sites, whereas at high ratios small clusters with bridging sites are formed. Substantial CO desorption from gem-dicarbonyl sites occurs under conditions of excess O2 but these species may be reformed in the presence of CO only. The gem-dicarbonyls are not active for the reaction while both linear and bridge-bonded species react. For all net-oxidising conditions, a rhodium oxide is formed, although this leads to substantial deactivation of the catalyst only for the most extreme cases studied here.