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 Mossbau er 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 formatio n of Co9S8-like species at the outer zeolite surface. In the presence of water, this process proceeds via the intermediate formation of a we ll-ordered ''CoS1+x'' phase (NiAs structure). Water removal prior to s ulfidation retards the formation of Co9S8-like species. This retardati on in Co9S8 formation is found to be more effective for CaY-zeolite th an for NaY-zeolite, which means that a larger part of the formed ''Co- sulfide'' is preserved in highly dispersed ''Co-sulfide'' particles. T hese findings are clearly different from those obtained earlier with i on exchanged CoNaY(ion ex) samples, for which drying prior to sulfidat ion resulted in very small ''Co-sulfide'' species with no resemblance to ''Co9S8''.