Brazilian limonite for the oxidation of quinoline: high activity after a simple magnetic separation

Abstract

Natural limonite, after a simple magnetic separation, was investigated as a low-cost catalyst in a Fenton-like system. The materials were characterized with temperature-programmed reduction (TPR), infrared spectroscopy, N2 adsorption/desorption, and 57Fe Mössbauer spectroscopy. Results showed that the main iron oxide phases in the materials were goethite (αFeOOH) and maghemite (γFe2O3) before and after the magnetic separation, respectively. The catalytic tests were carried out using quinoline as a model compound because it simulates the behavior of an important class of pollutants present in the fuel, i.e., nitrogen-containing compounds from contaminated petroleum. Quinoline was found to be oxidized through a successive hydroxylation mechanism. These results strongly suggest that highly reactive hydroxyl radicals, generated during the reaction involving H2O2 on the catalyst surface, are responsible for this oxidation and confirm that the material is an efficient heterogeneous Fenton-like catalyst.