The structure of well defined SiO2 supported MoO3 clusters during sulfidation : an in situ EXAFS-study

The sulfidation of a well defined MoO3/SiO2 catalyst has been examd. by means of TPS, EXAFS, and TEM. The oxidic clusters in a 5.6 wt% MoO3/SiO2 catalyst are transformed into almost completely sulfided particles (MoOxSy) by O-S exchange at RT. A molybdenum-sulfido particle that resembles the MoS3 structure is formed during sulfidation at 423 K. The MoS2 phase is formed at temps. between 523 and 573 K. The transition of MoS3 into MoS2 can be monitored by evolution of H2S from the catalyst, with simultaneous consumption of H2. The two dimensional size of the MoS2 slabs can be derived from the EXAFS Mo-Mo coordination no. by means of a theor. model. The stacking height of the slabs must be elucidated by TEM. [on SciFinder (R)