Identification of 'Co-sulfide' species in sulfided Co and CoMo catalysts

An investigation is presented on the identification of Co-sulfide species present in sulfided Co and CoMo catalysts. Both Mossbauer emission spectroscopy (MES) and x-ray absorption spectroscopy (EXAFS, XANES) were applied. As the structure of the catalyst is influenced by the treatment applied to it, a systematic study was undertaken in which measurements are performed in series. Between successive measurements only one external parameter was changed so that obsd. changes can be related to that particular parameter. By changing in this way the sulfidation temp., the Co-loading, the absence/presence of Mo, the support material (carbon or alumina) and (in the case of an alumina-support) the calcn. procedure, a framework of data was obtained. Based on trends obsd. in the MES and EXAFS results, a model is proposed for supported Co(-Mo) catalysts that can explain all the authors' results. In this model the Co in a sulfidic CoMo catalyst is present in very small particles in which part of the Co atoms may be four- and part six-fold coordinated with sulfur atoms. [on SciFinder (R)]