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

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.