AN EXAFS STUDY ON THE SO-CALLED CO-MO-S PHASE IN CO/C AND COMO/C, COMPARED WITH A MOSSBAUER EMISSION-SPECTROSCOPY STUDY

EXAFS measurements were performed on four sulfided catalysts with the same composition as their Co-57-containing counterparts which were previously characterized by Mossbauer emission spectroscopy. It was shown that the Co species in Co(373)/C catalysts with a "Co-Mo-S"-like Mossbauer emission spectrum after sulfidation at 373 K is similar to the species with the Co-Mo-S spectrum in CoMo/C catalysts. In both cases the Co atoms are present in a very highly dispersed Co species. In the catalyst without Mo this sulfidic Co species strongly sinters during sulfidation at 673 K, resulting in a Co9S8-type phase. In the CoMo/C catalyst, the Mo hinders sintering of the Co species.