Catalytic reduction of aqueous nitrates by metal supported catalysts on Al particles

• Metal catalysts loaded on elemental Al effectively reduce nitrate.
• 0.4%Pd–4%Cu/Al presents the best nitrogen selectivity of 34.1% at pH 4.0 and 4 h.
• Nitrate converts to nitrite on Al and Cu surface, and to nitrogen on Pd surface.
• Intermediate nitrite and adsorbed H on Pd surface are crucial for nitrogen formation.

To facilitate the reduction of nitrate to nitrogen in water, a class of mono- or dual-catalyst particles was prepared by loading mono-metals (Cu, Ni) or bimetals (Pd–Cu, Pt–Cu, Au–Cu, and Ru–Cu) on Al particles. The prepared catalyst-loaded Al samples were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy analysis. Batch kinetic experiments indicate that 0.4%Pd–4%Cu/Al at pH 4.0 resulted in the highest selectivity for nitrogen (N2). Kinetic studies reveal that nitrate can be first reduced to nitrite on the Al and Cu surface at a relatively slow rate and subsequently was rapidly reduced to nitrogen on the noble metal surface and to ammonia on the Al and Cu surface. The selectivity for nitrogen formation can be influenced by the type of metals deposited and the concentration of intermediate nitrite and atomic hydrogen adsorbed on the Pd surface.

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