Application of Mössbauer Emission Spectroscopy to the Study of Cobalt-Molybdenum Hydrodesulfurization Catalysts

Abstract

The need for reducing sulfur pollution has made hydrodesulfurization an important catalytic process for removing sulfur from oil fractions. Hydrodesulfurization, HDS, is commonly carried out by passing oil, together with hydrogen, over a sulfided catalyst consisting of cobalt and molybdenum supported on a high surface area alumina. In this way the sulfur is removed as H2S. For many years the structure of HDS catalysts has been the subject of extensive research efforts. Nevertheless, until recently, the nature of the catalytically active phase has been a subject of great controversy [1–5]. The first investigation of HDS catalysts using Mössbauer spectroscopy was published in 1975 [6]. In this study part of the cobalt atoms in the catalysts were replaced by iron-57 atoms in order to allow absorption spectra to be obtained. In subsequent investigations the catalysts have been doped with cobalt-57 and used as sources in Mössbauer emission studies [7-14]. Catalysts in which all the cobalt has been replaced by iron have also been studied [9,12].