Effects of CeO 2-ZrO 2 present in Pd/Al 2O 3 catalysts on the redox behavior of PdO x and their combustion activity

Abstract

The ceria-zirconium-modified alumina-supported palladium catalysts are prepared using impregnation method with H 2PdCl 4 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 Al 2O 3-rich grains surfaces, and a stable PdO species due to the strong interaction between PdO and CeO 2-ZrO 2 on the Ce-Zr/Al 2O 3 surfaces. The catalytic activity is strongly related to the redox behavior of PdO species highly dispersed on Ce-Zr-rich grains and Al 2O 3-rich grains surfaces, and the higher the reducibility of the PdO species, the higher the catalytic activity. The presence of Ce-Zr in Pd/Al 2O 3 catalyst would inhibit the site growth of PdO x particles and decomposition of PdO to Pd 0, and the reoxidation property of Pd 0 to PdO x is significantly improved, which obviously increases thermal stability and catalytic activity of Pd/Ce-Zr/Al 2O 3 catalyst for the methane combustion.