Hydroprocessing catalyst research focuses on Ni,Co/Mo,W catalysts.  Consequently, there is always a search for new alternatives.  The growing body of concerning the ability of nickel phosphide to catalyze hydroprocessing reactions has motivated this study.            Early literature preparations of nickel phosphide by the Oyama group utilized high temperature (~550oC) reduction of a nickel phosphate precursor creating bulk phosphide catalysts with surface areas less than 5 m2/g.  Attempts to support low loadings of the precursor on noninteracting supports with the same high temperature reductions has provided only slight advantages.  To date, an industrially viable simple route to high activity nickel phosphide catalysts remains elusive.                     Our goal was to find a route to a higher surface area nickel phosphide preferably by using low temperature reductions.  Since most hydrotreating units use sulfiding feeds in pretreatment, we looked at incorporating a component into the high surface area precursor that contained nickel and oxidized phosphorus and that would allow the dissociation of hydrogen even in the presence of H2S.   A logical choice would be use of MoS2 as a hydrogen dissociation component.  We also discovered that molybdenum can be structurally substituted into hydrothermally synthesized Ni H phosphite hydroxide precursors, with the molybdenum substitution enhancing the surface area of these precursors and the Ni phosphide phases formed on reduction in H2S/H2.  During this pretreatment, dispersed islands of MoS2 segregate from the precursor and provide a pathway for H2 dissociation that allows reduction of the phosphite precursor at substantially lower temperatures than in the absence of the MoS2.  We achieved surface areas of around 50 m2/g of well characterized Ni and Co-Ni bulk phosphides by this procedure, an order of magnitude higher than by the conventional approach.            We will discuss the implications of the catalytic data on what would be needed to achieve comparable activities to conventional catalysts.

Can nickel phosphides become viable hydroprocessing catalysts?

248th National Meeting (2014)

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