Observation of in situ reduction of ceria-supported rhodium catalysts by electron beam irradiation

Abstract

In rhodium catalysts supported on lanthanide oxides, significant difference in rhodium dispersions has been observed between cerium dioxide (CeO2) and sesquioxides (Ln2O3) by high resolution electron microscopy (HREM). This has been attributed to the different behaviors of the oxide supports during their impregnation with aqueous solution of rhodium nitrate (Rh(NO3)3). In the acid media, cerium dioxide has a higher reducibility while the sesquioxides have a higher solubility. So studying the catalyst precursor and the reduction process can provide an understanding of its interaction with the support during the impregnation stage and the metal dispersion on the oxide supports. Results on cerium dioxide support are presented here.The catalyst precursor was prepared by incipient wetness impregnation method as reported elsewhere. The rhodium loading was 2.4 wt%. The HREM work was performed in JEOL 4000EX electron microscope (point resolution of 1.7 Å). The typical current density used during observation was ∼6.5A/cm2 at the specimen. The vacuum in the column of the microscope was ∼10-7 torr.