Characteristics of Rh-SiO2 catalyst prepared using microemulsion - An investigation from the behavior of adsorbed CO species

Spectroscopic investigations were conducted to elucidate the difference in surface properties between two kinds of Rh-SiO2 catalysts prepared by using microemulsion and by the conventional impregnation method, by means of FT- IR measurements using CO as a probe molecule. The gem-dicarbonyl species ad sorbed on isolated Rh-I sites were observed in the IR spectra of the Rh-SiO 2 catalyst prepared by using microemulsion even at a temperature as high as 300 degrees C, while it was not observed at this temperature in the spectr a of the Rh-SiO2 catalysts prepared by the impregnation method. This result suggested that the disruption of Rh clusters caused by CO gas, leading to the formation of isolated Rh-I sites, still occurred prominently on the Rh- SiO2 catalysts prepared by using microemulsion even at such a high temperat ure that agglomeration occurred on the catalyst prepared by the impregnatio n method. It is quite likely that the disruption occurred prominently becau se the Rh particles of the catalyst existed in an oxidized state. Therefore , the oxidation state of Rh particles was investigated by XPS measurements, which showed that there were more Rh atoms in an oxidized state in the Rh- SiO2 catalyst prepared by using microemulsion. It is concluded, therefore, that the Rh-SiO2 catalyst prepared by using microemulsion had significant f eatures attributed to a strong interaction between Rh particles and SiO2 su pport.