Liquid phase hydrogenation and hydrodenitrogenation of aromatic nitrogen-containing environmental pollutants

Carcinogenic aromatic nitro-compounds are hydrogenated at 80–140 °C in the presence of a silica sol–gel entrapped combined palladium-[Rh(cod)Cl]2 catalyst to give hydroaromatic amines and nitrogen-free hydrocarbons. The process involves initial transformation of the nitro to an amino function. Further hydrogenation causes denitrogenation and saturation of the aromatic moieties. Using 1-aminonaphthalene as a model substrate reveals simultaneous formation of 1- and 5-aminotetralin. While the former amine is readily converted into tetralin and 1-aminodecalins, the 5-aminotetralin gives, in a slow process, only the aminodecalins. The latter compounds are slowly denitrogenated to decalins. The catalytic hydrogenation of the aromatic compounds is accompanied by NH3 elimination by which secondary amines are formed in a reversible fashion. The entrapped catalyst is leach-proof and recyclable. However, its catalytic activity in the different steps changes during the recycling. The high activity of the combined catalyst results from synergism between the two different metal nuclei.

Graphical abstractIn the presence of a silica sol–gel entrapped catalyst composed of metallic palladium and [Rh(cod)(μ-Cl)]2 under 27.6 bar H2 at 80–140 °C carcinogenic nitro- and amino-polycyclic aromatic hydrocarbons are hydrodenitrogenated. Using 1-nitronaphthalene as a model compound, it was found that initially the nitro-compounds are reduced to mixtures of primary and secondary amines that ultimately form polycylic alicylic hydrocarbons and ammonia.Figure optionsDownload full-size imageDownload as PowerPoint slide