Modification of PdO/CeO2–ZrO2 catalyst by MnO x for water–gas shift reaction: redox property and valence state of Pd

Abstract

A PdO/MnO x /CeO2–ZrO2 catalyst was prepared by a two-step impregnation method. PdO/CeO2–ZrO2, PdO/Al2O3, PdO/MnO x /Al2O3, CeO2–ZrO2, and MnO x /CeO2–ZrO2 catalysts were also prepared for reference. The textural and surface properties of the catalysts were characterized by X-ray diffraction, Brunauer–Emmett–Teller, Raman spectroscopy, X-ray photoelectron spectroscopy, ultraviolet visible spectroscopy, and CO chemisorption. The redox properties and catalytic activity of the catalysts were evaluated by H2 temperature-programmed reduction (H2-TPR) and water–gas shift (WGS) reaction measurements, respectively. The addition of manganese oxide enhances the WGS activity of PdO/CeO2–ZrO2 catalyst significantly. It is ascribed to the improved redox property of the catalyst arising mainly from the Mn–Ce interaction at the interface and the formation of metallic Pd species that resulted from interacting with manganese oxide.