Highly efficient hydrogenation reduction of nitrate to ammonia and nitrogen via a Ni-MOF-74 reduction-derived Ni-based catalyst

Abstract

The design of highly efficient catalysts is important for developing sustainable energy conversion techniques. Nickel-based MOF-derived catalysts are a class of materials synthesized by transforming metal organic frameworks containing nickel into heterostructures. In this work, a novel and efficient Ni-MOF-74-derived catalyst was developed for the catalytic hydrogenation reduction of nitrate to ammonia and nitrogen. The reaction factors, including reaction temperature, initial concentration, and interfering ions, were systematically investigated. The optimized catalyst exhibited high activity, with a nitrate removal rate of over 90% and an ammonia selectivity of 66.5% under mild conditions. The kinetic analysis results indicate that NO₃⁻ degradation conforms to a first-order kinetic reaction, and the apparent activation energy was 23.67 KJ mol⁻¹. The characterization results, including XRD, XPS and SEM, confirmed the formation of highly dispersed metallic nickel within the carbon carrier. The carbon support could stabilize Ni nanoparticles as well as improve electron transfer, and the presence of Ni²⁺ species could be conducive to enhancing NO₃⁻ adsorption and modulating the local reaction environment, which was responsible for its high activity and selectivity in the catalytic nitrate reduction to ammonia and nitrogen. Besides, the nitrate hydrogenation reduction mechanism undergoes a multi-step hydrogenation pathway to ammonia and nitrogen over the Ni-MOF-74-derived catalyst. This work highlighted the strong potential of Ni-MOF-74-derived catalysts for hydrogenation reduction and provided a promising approach to sustainable nitrate wastewater treatment coupled with resource recovery.