Pd-Ce-Ox species on MWCNTs surface: Probing the structure-activity correlation in low-temperature CO oxidation

Abstract

Herein, the highly dispersed palladium and ceria species were deposted on the surface of multi-walled carbon nanotubes (MWCNTs) by co-deposition from acetone solutions. The use of MWCNTs allowed varying Pd/Ce atomic ratio in a wide range, while maintaining a high dispersion of the active components. Application of physicochemical methods revealed the formation of various palladium species. Single Pd2+ ions dispersed in CeO2 lattice were the main Pd-Ce-Ox species at low Pdat/Ceat ratio. With an increase of the Pd content in the samples the preferential formation of PdO particles in a tight contact with CeO2 nanoparticles was observed. The size of PdO and CeO2 primary particles was in a range of 1–5 nm.The Pd-Ce-Ox/MWCNTs samples showed high activity in the CO oxidation reaction already at room temperature with a temperature of 50% CO conversion below 100 °C. The Pd2+-CeO2 and PdO-CeO2 species demonstrated the comparable activity in “dry” CO oxidation. However, the presence of water vapor in the reaction mixture resulted in the immediate deactivation of Pd2+-CeO2 species, while PdO-CeO2 species retained a high activity at 20°С. The results of the work highlight the benefits of MWCNTs, Pd, and CeO2 combination for obtaining catalysts highly active in CO oxidation.