Influence of water on the Sulfidation of Co/NaY and Co/CaY prepared by impregnation, a Mossbauer emission spectroscopy and EXAFS study

The influence of physisorbed water on the sulfidation of impregnation type Co/NaY(imp) and Co/CaY(imp) catalysts which contain about 4 wt % Co and are prepared via pore volume impregnation is studied by Mossbauer emission spectroscopy and extended X-ray absorption fine structure. It is found that in the absence as well as in the presence of water, sulfidation of the impregnated samples finally results in the formation of Co9S8-like species at the outer zeolite surface. In the presence of water, this process proceeds via the intermediate formation of a well-ordered ''CoS1+x'' phase (NiAs structure). Water removal prior to sulfidation retards the formation of Co9S8-like species. This retardation in Co9S8 formation is found to be more effective for CaY-zeolite than for NaY-zeolite, which means that a larger part of the formed ''Co-sulfide'' is preserved in highly dispersed ''Co-sulfide'' particles. These findings are clearly different from those obtained earlier with ion exchanged CoNaY(ion ex) samples, for which drying prior to sulfidation resulted in very small ''Co-sulfide'' species with no resemblance to ''Co9S8''.