Pd Supported on CeO₂ Nanostructures Prepared by Planetary Ball Milling under a Modified Atmosphere for Catalytic...

Pd catalysts supported on CeO₂ (1 wt % Pd) were synthesized using dry mechanochemical and incipient wetness impregnation methods. The mechanochemical synthesis was conducted in a planetary ball mill for 10 min with YSZ milling jar and balls at velocities ranging from 100 to 1000 rpm under various atmospheres (air, N₂, O₂, and 5% H₂/N₂). Catalysts were evaluated for their performance in the CO oxidation reaction and characterized at the nanoscale using Raman spectroscopy, XPS, XRD, H₂-TPR, XRF, nitrogen adsorption/desorption, and HAADF-STEM-EDX. Increased catalytic activity was observed in samples milled at lower velocities (100-250 rpm) in air, outperforming that of the conventional sample prepared by impregnation. This improvement appears to be attributed to changes in the surface nanostructure related to the metal-support interaction rather than the presence of oxygen vacancies. XPS revealed a higher concentration of PdO _x -Ce species in the most active milled sample, suggesting this as a reason for its superior catalytic performance. On the other hand, HAADF-STEM-EDX showed the presence of 2-3 nm Pd nanoparticles as well as Pd atoms/clusters anchored on crystalline ceria in the most active milled sample. Samples milled at high velocity (850-1000 rpm) showed a high degree of structural defects in the ceria crystallites and increased Ce³⁺ species, but their catalytic performance was lower than the samples milled at low velocity. This study highlights the impact of milling conditions on the nanostructure and catalytic properties of Pd/CeO₂ catalysts, with low-velocity milling emerging as a promising approach for enhancing catalytic activity.