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Abstract
Motivated by increased awareness about nitrate contamination of surface waters and its deleterious effects in human and animal health, we sought an alternative, non-noble metal catalyst for the chemical degradation of nitrate. First-row transition metal phosphides recently emerged as excellent alternatives for hydrogen evolution and hydrotreating reactions. We demonstrate that a key member of this family, Ni2P readily hydrogenates nitrate (NO3-) to ammonia (NH3) near ambient conditions with very high selectivity (96%). One of the few non-precious metal-based catalysts for this transformation, and among ca. 1% of catalysts with NH3 selectivity, Ni2P can be recycled multiple times with limited loss of activity. Both nitrite (NO2-) and nitric oxide (NO) interme-diates are also hydrogenated. Density functional theory (DFT) indicates that—in the absence of a catalyst—nitrite hydrogenation is the reaction bottleneck. A variety of adsorbates (H, O, N, NO) induce surface reconstruction with top-layer Ni-rich surface stoi-chiometry. Critically, H saturation coverage on Ni2P(001) is only ca. 3 nm-2, significantly less than that on Pd(111) and Ni(111) of ca. 15-18 nm-2, which may play a key role in allowing coadsorption of NOx-. The ability of Earth-abundant, binary metal phos-phides such as Ni2P to catalyze nitrate hydrogenation could transform and help us better understand the basic science behind catalytic hydrogenation and, in turn, advance the next generation of oxyanion removal technologies.