Noble metal promoted molybdenum oxide

We begin with the structure of a noble metal catalyst. The emphasis is on the preparation of rhodium on aluminum oxide and the nature of the metal-support interaction. Next we focus on a promoted surface in a review of potassium on noble metals. This section illustrates how single crystal techniques have been applied to investigate to what extent promoters perturb the surface of a catalyst. The third study deals with the sulfidic cobalt-molybdenum catalysts used in hydrotreating reactions. Here we are concerned with the composition and structure of the catalytically active... 

The conventional nickel-based catalysts could be modified by adding oxide promoters such as potassium, lanthanam, cerium, and molybdenum in the catalyst formulations. It is believed that the added promoters improve the dispersion of nickel metal on the catalyst surface, thereby reducing the chance of carbon accumulation. Noble metals such as Pd, Pt, Ru, and Ir have been found to be more carbon tolerant as the solubility of carbon is less in these metals.54-57 However, they are more expensive than nickel-based catalyst, and as a consequence, they are less attractive for large-scale commercial applications. Alloying of nickel with other base metals such as Cu, Co, or noble metals such as Au, Pt, and Re has also been found to decrease... 

A general explanation cannot be given, which is valid for different catalysts and reactions, even if these are limited to HDS. One of the characteristic examples is the essential difference in the mechanism of catal3dic effect on sulfided noble metals in comparison with that of molybdenum and tungsten-oxide based catalyst, due to large differences in the energy of their sulfide formation. This difference in HDS mechanism is also well seen from the rather different effect of sulfidation on precious metal promoted MoOx, in comparison with CoMoOx, in the initial period of sulfidation. 

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