An efficient reduction of unsaturated bonds and halogen-containing groups by nascent hydrogen over Raney Ni catalyst

Presence of unsaturated bonds and halogen-containing groups is the most common characteristic of toxic and harmful environmental pollutants. Herein, catalytic hydrogenation was chosen as a water quality control method for such contaminants. Considering the safety, availability and activity of the hydrogen source, electrochemical in situ hydrogen generation was introduced. Under the combined action of Raney Ni (R-Ni) and nascent hydrogen (Nas-H₂), three compounds (50 mg L^-1, 90 ml), i.e., acrylamide, 2, 6-dibromo-4-nitrophenol and 2-chloro-4-fluorobenzonitrile achieved complete hydrogenation reduction in a short time. The improved system realized the quantitative consumption of hydrogen source and the efficient operation of hydrogenation reaction under mild conditions. Additionally, the alkaline environment formed by hydrogen evolution reaction (HER) avoided secondary pollution caused by catalyst dissolution. Atomic hydrogen (H·) produced from R-Ni and Nas-H₂ was the active free radical of the reaction. The hydrogenation activities of different functional groups were obtained according to the following order: Ph-NO₂ ＞ -C = C- ＞ Ph-C≡N ＞ Ph-Br ＞ Ph-Cl ＞ Ph-F. This work indicates that the catalytic hydrogenation system consisting of R-Ni and Nas-H₂ is a promising technology to reduce unsaturated bonds and halogen-containing groups.