Co-Mo Hydrodesulfurization Catalysts Studied by EXAFS

Abstract

Hydrotreating reactions, and in particular the hydrodesulfurization (HDS) reaction, are among the most important catalytic processes. This has, of course, inspired massive research efforts in order to understand the structural and chemical form of the elements in the catalysts used in such reactions (i. e. sulfided Co-Mo/Al₂O₃ and Ni-Mo/Al₂O₃ catalysts). Great efforts have been made to establish possible connections between such structural properties and the various catalytic functions. Despite the numerous studies, greatly diverging views on these properties exist (see e. g. [1, 2]). It has recently been shown that the promotion of the HDS activity of both supported and unsupported Co-Mo catalysts can be related to the presence of the Co promoter atoms in a so-called Co-Mo-S phase [3, 4]. The characterization of the Co-Mo-S phase was carried out by use of Mössbauer emission spectroscopy [5] and EXAFS at both the Co and Mo K edges [6–8]. These studies indicated that Co-Mo-S can be considered as Co atoms located at the edge positions of an MoS₂-like structure. Supporting evidence of this picture has recently been given by infrared and electron microscopy studies [9].