Catalytic reduction of nitrite in water over ceria- and ceria-zirconia-supported Pd catalysts

In this study, we tested Pd/Ce_{1 - x}Zr_xO₂ catalysts (x = 0, 0.3, 0.5 and 0.7) for nitrite reduction in water. The Ce_{1 - x}Zr_xO₂ was synthesized by the co-precipitation method, and Pd was impregnated on the support using the deposition-precipitation method. The introduction of Zr into the ceria lattice of the catalyst with x = 0.3 and 0.5 distorted the lattice structure, accordingly, both the catalysts easily reduced nitrite than the pure CeO₂ supported Pd catalyst. In contrast, the Pd/Ce_0.3Zr_0.7O₂ (x = 0.7) catalyst became difficult to reduce as the tetragonal ZrO₂ phase was dominant in the catalyst structure. These phenomena led to the difference in the amount of oxygen vacancies on the surface of the catalyst. In the nitrite reduction test, the catalyst containing more oxygen vacancies showed higher activity. The relationships between the catalytic activities and the surface properties with composition of the support over Pd/Ce_{1 - x}Zr_xO₂ catalysts were investigated by X-ray diffraction (XRD), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) analyses.