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Molybdenum sulfide catalysts have long been used for hydrotreating petroleum fractions. In most industrial uses, the catalysts contain nickel or cobalt as a promoter and are supported on porous materials such as alumina. Such promoters significantly enhance the catalytic activities of molybdenum sulfide catalysts, so the structures of the promoted catalysts, namely Ni_Mo (W) or Co_Mo binary sulfides supported on alumina, have been intensely studied for both scientific and practical interests. By 1980, at least three structural models1)~3) had been proposed as the active catalytic sites of the binary sulfide systems. In all the models, coordinatively unsaturated sites (CUS) of molybdenum (or tungsten) disulfide with a layered structure act as the active center for hydrodesulfurization (HDS) or hydrogenation (HYD), although the function of the nickel or cobalt differs between the three models. Subsequently, the “Co(Ni)MoS” phase4),5) has been widely accepted as the active catalytic center of the binary sulfide catalysts. In the Co(Ni)MoS phase, Co or Ni atoms are located at the edges of the MoS2 sheets. The sulfur atoms bonded to the Co or Ni are more easily dissociated than those bonded to Mo and thus form highly active catalytic sites. In fact, the function of the Co or Ni atoms is not a catalyst promoter but as an active catalytic center. The common conclusions of the old structural models and the CoMoS model indicate that the dispersion and morphology of MoS2 structures on the catalyst supports are important factors to improve the catalytic performances of binary sulfide catalysts. Our group has been studying the catalytic performances and structures of molybdenum sulfide-based catalysts, aiming at the development of high performance hydrotreating catalysts for heavy hydrocarbon feedstocks. During the course of the study, we found that the catalyst support species significantly affected the catalytic functions of the molybdenum sulfide catalysts. Therefore, we speculated that the morphology and dispersion of the molybdenum sulfide were controlled by the electronic interactions and geometric relationships between the catalysts and supports. The present review introduces a series of our studies on the relationship between the catalytic functions and the 46 Journal of the Japan Petroleum Institute, 59, (2), 46-58 (2016)

Morphology, Dispersion and Catalytic Functions of Supported Molybdenum Sulfide Catalysts for Hydrotreating Petroleum Fractions