Pd Supported on CeO Nanostructures Prepared by Planetary Ball Milling under a Modified Atmosphere for Catalytic Oxidation of CO.

Pd catalysts supported on CeO (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, N, O, and 5% H/N). Catalysts were evaluated for their performance in the CO oxidation reaction and characterized at the nanoscale using Raman spectroscopy, XPS, XRD, H-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 -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 Ce 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/CeO catalysts, with low-velocity milling emerging as a promising approach for enhancing catalytic activity.