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

Composite catalysts consisting of Rh–CeO_x 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 Rh_at/Ce_at = 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 RhO_x particles are found to form in all samples studied. When the Rh_at/Ce_at ratio is changed, structures are formed that exhibit the catalytic activity in the CO oxidation reaction for different temperature ranges. At low Rh_at/Ce_at ratios (< 0.17) the CO conversion is observed at temperatures above 100 °C. When the Rh_at/Ce_at 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 Rh_at/Ce_at ratio reveal that structures based on dispersed oxidized rhodium particles modified by Ce³⁺ ions can be active species.