Structural and Catalytic Properties of Rh–CeO2/MWCNT Composite Catalysts

Composite catalysts consisting of Rh–CeOx structures supported on the surface of multi-walled carbon nanotubes (MWCNTs) are studied. For supported active components (Rh, Ce) the rhodium content is maintained constant on the MWCNT surface and the cerium concentration is varied in the range Rhat/Ceat = 0.085-0.34. The obtained samples are investigated by a combination of structural (X-ray diffraction, transmission electron microscopy (TEM)), spectral (X-ray photoelectron spectroscopy (XPS)), and kinetic (temperature-programmed reaction with CO (TPR-CO) and CO+O2 (TPR-CO+O2)) techniques. Highly dispersed CeO2 and RhOx particles are found to form in all samples studied. When the Rhat/Ceat ratio is changed, structures are formed that exhibit the catalytic activity in the CO oxidation reaction for different temperature ranges. At low Rhat/Ceat ratios (< 0.17) the CO conversion is observed at temperatures above 100 °C. When the Rhat/Ceat ratio increases, centers exhibiting the catalytic activity at temperatures below 0 °C are formed in Rh–CeO2/MWCNT catalysts. HR-TEM and TPR-CO studies of composite catalysts with a high Rhat/Ceat ratio reveal that structures based on dispersed oxidized rhodium particles modified by Ce3+ ions can be active species.