Room-Temperature Catalytic Reduction of Aqueous Nitrate to Ammonia with Ni Nanoparticles Immobilized on an Fe3O4@n-SiO2@h-SiO2–NH2 Support

Abstract

Efficient and selective catalytic reduction of aqueous nitrate to ammonia was achieved over Ni nanoparticles immobilized on Fe3O4@n-SiO2@h-SiO2–NH2 [a magnetic hierarchical mesoporous amine-functionalized (M-HMAF) silica] by using hydrazine hydrate as a reducing agent. The high hierarchical mesoporous structure (surface area of 416 m2 g–1 and pore size of 3.7 nm) and Fe3O4 core (ca. 7 nm) of the M-HMAF silica support resulted in a high dispersion of Ni nanoparticles over the support and easy recovery of the catalyst, respectively. Interestingly, the Ni/M-HMAF silica catalyst exhibited an excellent catalytic turnover (275 mmol gmetal–1 h–1) compared with most of the existing catalysts for the conversion of nitrate ions at room temperature. The mechanistic study using UV/Vis spectroscopy revealed that the catalytic conversion of nitrate ions to ammonia proceeded through in situ generated nitrite ions. Subsequently, the ammonia produced from nitrate ions was isolated and analyzed by 1H and 15N NMR spectroscopy, whereas the N2 gas released as a byproduct of hydrazine was characterized by GC–MS. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim