Hydrotreating catalyst structure and reactivity

HDS catalysts have been characterized extensively with a wide variety of tools, and several extensive reviews of the subject have been presented (85,88-91). Substantial effort has been aimed at relating catalytic activity and selectivity to microscopic properties such as catalyst composition, electronic structure, and geometric structure. EXAFS investigations of working catalysts have provided information about the composition, average local coordination, and interatomic distances of atoms in the catalyst clusters. It has been concluded that the active phase under operating conditions is MoS2-like particles with a dimension of 10—20 A (92-94). 

Notwithstanding the impressive number of investigations of HDS catalysts, many fundamental questions remain unanswered, and most of them are obviously related to the fact that traditional spectroscopic techniques are not capable of unequivocally mapping the real-space atomic structure. For instance, what is the preferential shape of the M0S2 crystallites The basal planes of the M0S2 slabs are chemically inert, and it is therefore clear that the HDS activity is associated with the 

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Volume 48 Structure and Reactivity of Surfaces. Proceedings of a European Conference, Trieste, September 13-16, 1988 edited by C. Morterra, A. Zecchina and G. Costa Volume 49 Zeolites Facts, Figures, Future. Proceedings of the 8th International Zeolite Conference, Amsterdam, July 10-14, 1989. Parts A and B edited by P.A. Jacobs and R.A. van Santen Volume 50 Hydrotreating Catalysts. Preparation, Characterization and Performance. 

X-Ray Absorption Fine Structure, Mossbauer, and Reactivity Studies of Unsupported Cobalt-Molybdenum Hydrotreating Catalysts... 

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