Re-dispersion of Pd on Ce0.5Zr0.5O2 upon cooling in the presence of oxygen

• Re-dispersion of Pd on Ce0.5Zr0.5O2 was observed during slow cooling in oxidizing atmosphere.
• Sufficient cooling time, O2, and active support were the essential factors for re-dispersion.
• Sintered Pd particles were re-oxidized to PdOx and re-dispersed under the driving of the formation of PdOCe bonds.

Pd/Ce0.5Zr0.5O2 catalyst was prepared by impregnation method and subjected to different cooling procedures (rapid cooling vs. slow cooling in O2 or in He) after pretreated at 950 °C for 30 min. The obtained catalysts were characterized by CO chemisorption, transmission electron microscope (TEM), CO temperature-programmed oxidation (CO-TPO), X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis (TGA). The results revealed that Pd species on Ce0.5Zr0.5O2 (CZ) suffered severe sintering during high-temperature calcination, but the Pd dispersion increased remarkably after slow cooling in O2. Further investigations ascribed this phenomenon to the Pd re-dispersion process, which needed three essential factors, i.e. sufficient cooling time, oxidizing atmosphere and active support which had strong interaction with Pd species. The re-dispersion process was proved to be mainly due to both the re-oxidization of the sintered Pd particles and the slow migration of the PdOx under the driving of the interaction between Pd and CZ.

Scheme of the re-dispersion process of Pd on the Ce0.5Zr0.5O2 support in O2 at different cooling rates.Figure optionsDownload high-quality image (114 K)Download as PowerPoint slide