INFRARED STUDY OF CO OXIDATION OVER PT-RH/AL2O3 CATALYSTS

The oxidation of CO by oxygen over two alumina-supported Pt-Rh catalysts has been studied using FTIR and an in situ flow reactor cell. The catalysts were tested under light-off conditions (300-573 K) over a wide range of O2 : CO ratios (0.25-35 : 1). Invariance in the linear carbonyl stretching frequency during reaction was used as an indicator of the presence of ensembles containing only platinum atoms. Catalysts which were heated in CO at 573 K and rereduced prior to reaction showed an improvement in performance as a result of the formation of particulate rhodium at the expense of the inactive gem-dicarbonyl centres. This agglomeration of the dispersed rhodium phase was responsible for the incorporation of rhodium atoms into Pt or Pt-Rh particles. This led to the elimination of platinum only ensembles and subsequently to the formation of mixed CO/O adlayers during the reaction over catalyst prepared by coimpregnation of the metal salts. Ensembles containing only platinum atoms existed after these treatments for catalyst prepared by sequential impregnation of salts. © 1993 Academic Press, Inc.