Raney nickel coupled nascent hydrogen as a novel strategy for enhanced reduction of nitrate and nitrite

Raney nickel (R–Ni) is a cost-effective hydrogenation catalyst, and nascent hydrogen (Nas-H2) generated in situ on the cathode trends to more reactive than commercial hydrogen (Com-H2). In the present work, nitrate and nitrite (NOX-) reduction via R–Ni/Nas-H2 catalytic system was investigated. The results show that hydrogenation of NOX- (C0 = 3.0 mM) follows pseudo-first-order reaction kinetics with kinetic constants of 5.18 × 10-2 min-1 (NO3-) and 6.46 × 10-2 min-1 (NO2-). The saturation demand for Nas-H2 is only 0.8 mL min-1 at a fixed R–Ni dosage of 1.0 g L-1. The experiments reveal that both Nas-H2 and hydrogen adatoms (Hads∗) can drive the reduction of NOX-. The improved reduction ratios of NOX- are attributed to two aspects: (1) the micro/nano-sized Nas-H2 bubbles exhibits increased reactivity due to the fine dispersion of the hydrogen molecules; (2) the alkaline environment formed by the cathode positively maintain R–Ni activity, thus, Nas-H2 bubbles were more readily activated to generate powerful Hads∗. The results give insight into NOX- hydrogenation via introducing fine hydrogen resource, and can develop an efficient catalytic hydrogenation technique without noble metals.