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

• Pd/Ce1 − xZrxO2 catalysts were applied for nitrite reduction.
• Introduction of Zr into ceria lattice led to the formation of oxygen vacancy.
• The number of oxygen vacancies was dependent on the Zr content.
• The nitrite reduction activity was affected by the amount of oxygen vacancies.

In this study, we tested Pd/Ce1 − xZrxO2 catalysts (x = 0, 0.3, 0.5 and 0.7) for nitrite reduction in water. The Ce1 − xZrxO2 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/Ce0.3Zr0.7O2 (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/Ce1 − xZrxO2 catalysts were investigated by X-ray diffraction (XRD), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) analyses.

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