Deep hydrogenation of tetralin in the presence of dibenzothiophene over PtPd catalysts : influence of fluorine

Abstract

Deep hydrogenation can greatly enhance the quality of diesel fuel by removing poly-aromatic content to meet environmental regulations. Alumina-supported Pt, Pd and Pt-Pd catalysts are well known as noble metal catalysts which are widely used in the hydrogenation reaction at low temperatures, but these catalysts are very sensitive to sulfur. Thus, the aim of this work is to develop these catalysts to enhance the S-tolerance by adding controlled amounts of fluorine both before and after metal loading. Dibenzothiophene (DBT) is used as the S-containing molecule. All of the catalysts were prepared by incipient wetness impregnation and tested at a reaction temperature of 300C with a total pressure of 500 psig. The results showed that in the absence of sulfure, the addition of F before metal enhanced catalytic activity but the addition of F after metal reduced catalytic for all actalysts. The atomic surface composition obtained by XPS revealed that the oxygen concentration decreased with the addition of F because the incorporation of F replaces O or OH of the oxide catalysts. Noticeably, the concentration of residual CI on the surface, from the metal precursors, was reduced when F was added. XPS results showed that the addition of F before the metal gave higher metal dispersion (Pd:Al ratio) than the addition of F after the metal. In the presence of DBT, the F-promoted catalysts gave a higher tetralin conversion and higher sulfur tolerance than unpromoted catalysts. For the order of impregnation, the addition of F before the metal give a higher sufur tolerance than the addition of F after the metal.