Natural goethite reduced with dithionite: evaluation of the reduction process by XANES and Mössbauer spectroscopy and application of the catalyst in the oxidation of model organic compounds

Abstract

Iron oxides have been used as catalyst in different industrial applications, prominently in the petrochemical field. Natural goethites are interesting materials since they have a high surface area compared to their synthetic counterparts and also have a high relative abundance in the environment. Chemical treatment with sodium dithionite may cause surface changes of the goethite improving its catalytic activity. In this work, a natural goethite was used after dithionite treatment in the catalytic oxidation of methylene blue and quinoline. Infrared spectroscopy (FTIR) and temperature programmed reduction (TPR) were utilized for characterization. Quinoline oxidation by-products were monitored by electrospray mass spectroscopy (ESI-MS). After treatment, hydrogen peroxide decomposition was enhanced, indicating a radical mechanism. The same mechanism can be ascribed for the catalytic oxidation of quinoline since hydroxylation intermediates were observed. The same kind of mechanism can also be proposed for the methylene blue oxidation.