Green synthesis of 2-L ferrihydrite supported on steel slags as catalyst for the reduction of nitroarenes

Nitroarenes are a class of environmental pollutants generated by various industrial processes such as dye and pharmaceutical production. This harmful waste1 can be possibly valorised by reducing the nitro group to amine to obtain substituted anilines, which are highly valuable chemical intermediates. This study deals with the reduction reaction of nitroarenes employing hydrazine monohydrate as reducing agent and iron-supported steel slags as a novel heterogeneous catalyst. Steel slags (SS) are a waste product of steelmaking industry, characterised by the presences of silicates, carbonates and hydroxides2. SS present high alkalinity and can act as reactive support for iron, triggering the formation of catalytically active iron oxides/hydroxides, starting from inexpensive iron salts. A systematic study will be described regarding the catalytic activity of SS modified with the following salts (or mixtures): FeSO4·7H2O, FeCl3·6H2O, FeCl2·4H2O. All iron-supported steel slags revealed active in the hydrogenation of nitrobenzene with the best results achieved by the catalyst prepared from FeCl3·6H2O (referred as Fe3), for which the scope of the reaction was explored. The iron species active in catalysis is the 2L-ferrihydrite.