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

Pd/Ce0.5Zr0.5O2 catalyst was prepared by impregnation method and subjected to different cooling procedures (rapid cooling vs. slow cooling in O-2 or in He) after pretreated at 950 degrees 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 O-2. 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. (C) 2015 Elsevier B.V. All rights reserved.