Cu⁺ based active sites of different oxides supported Pd-Cu catalysts and electrolytic in-situ H₂ evolution for high-efficiency nitrate reduction reaction

Supported Pd-Cu NO₃⁻ reduction (NO₃R) under H₂ atmosphere is considered as a promising way to achieve NO₃⁻ removal directly in water through converting into N₂, which is a harmless product in environment. However, desirable NO₃R kinetics and N₂ selectivity remain challenges. In this research, 2.5 wt% Cu and 10 wt% Pd are loaded on various oxides supports and combine with electrolytic in-situ H₂ generation for NO₃R. Pd_10%Cu_2.5%/TiO₂ demonstrates a faster NO₃R rate constant than Pd_10%Cu_2.5%/γ-Al₂O₃ and even greater than Pd_10%Cu_2.5%/CeO₂. Pd_10%Cu_2.5%/γ-Al₂O₃ obtains better N₂ selectivity than the other two. Crucially, the oxygen vacancies (V_O) existing in TiO₂ and CeO₂ can reduce the nearby Cu²⁺ to Cu⁺, also Cu²⁺ can attract electrons from Pd⁰ to form Cu⁺ on the γ-Al₂O₃ surface. Verified by experiments and density functional (DFT) calculations, these Cu⁺ based active sites on the surface of substrates are vital for effective NO₃⁻ adsorption and high N₂ selectivity.