Effects of CeO2-ZrO2 present in Pd/Al2O3 catalysts on the redox behavior of PdOx and their combustion activity

The ceria-zirconium-modified alumina-supported palladium catalysts are prepared using impregnation method with H2PdCl4 as Pd source, hydrazine hydrate as reducing agent. The physicochemical properties of these catalysts are characterized by BET surface area (BET), X-ray powder diffraction (XRD), transmission electron microscopy (TEM), temperature programmed reduction (H-2-TPR) and temperature programmed oxidation (O-2-TPO) techniques, and their catalytic activities for the combustion of methane are examined. The results show that the palladium mainly exist in a highly dispersed PdO species on Ce-Zr-rich grains as well as Al2O3-rich grains surfaces, and a stable PdO species due to the strong interaction between PdO and CeO2-ZrO2 on the Ce-Zr/Al2O3 surfaces. The catalytic activity is strongly related to the redox behavior of PdO species highly dispersed on Ce-Zr-rich grains and Al2O3-rich grains surfaces, and the higher the reducibility of the PdO species, the higher the catalytic activity. The presence of Ce-Zr in Pd/Al2O3 catalyst would inhibit the site growth of PdOx particles and decomposition of PdO to Pd-0, and the reoxidation property of Pd-0 to PdOx is significantly improved, which obviously increases thermal stability and catalytic activity of Pd/Ce-Zr/Al2O3 catalyst for the methane combustion. (C) 2008 Elsevier B.V. All rights reserved.