Enhanced catalytic performance of Ce-MCM-41-supported Rh for CO oxidation

Abstract

1wt%Rh/Ce-MCM-41 catalysts were prepared by the incipient wet impregnation method using mesoporous Ce-MCM-41 materials as supports where the Si/Ce molar ratios varied from 10 to 50. The structural properties and physicochemical features of the catalysts were characterized with a variety of techniques such as N2 physisorption, X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The CO adsorption–desorption behaviors on the catalysts were explored with in situ Fourier-transform infrared (FTIR) spectroscopic technique. The light-off curves of CO oxidation achieved on the Rh/Ce-MCM-41 catalysts significantly shifted toward lower temperature range compared to that achieved with the Rh/CeO2 and Rh/MCM-41 reference catalysts. The Rh/Ce-MCM-41 catalysts exhibited high activity with complete CO conversion at temperatures near 440 K. The in situ CO-FTIR spectra confirmed that several forms of Rh−O, Rh2−CO, Rh3−CO and Rh−(CO)2 carbonyl species with linear, bridged, hollow and gem-dicarbonyl bonds were formed. CO preferentially adsorbs on highly dispersed Rh clusters to form gem-dicarbonyl species. A reaction mechanism was proposed based primarily on the formation of intermediary species of CO adsorbed over Rh3+ clusters and the active O···OH oxygen species present on the surface in combination with the incorporation of Ce4+ ion into the framework of MCM-41 material. These findings suggest that the deposition of the Rh phase on the ceria-modified mesoporous supports could remarkably promote CO oxidation at low temperatures.