A critical requirement of a hydrotreating catalyst is resistance to deactivation by sulfur under the harsh reaction conditions found in a hydrotreating reactor. Transition metal phosphides exhibit high activities for heteroatom (S, N, O) removal reactions with nickel phosphide (Ni2P) reported to be more active than commercial sulfided Co-Mo/Al2O3 and Ni-Mo/Al2O3 catalysts, yet the importance of sulfur poisoning for metal phosphides remains poorly understood. In the current study, the effect of particle size on sulfur resistance of Ni2P catalysts for dibenzothiophene hydrodesulfurization (HDS) was assessed using well-defined Ni2P nanoparticles (5.9, 11.2 and 17.1 nm) encapsulated in mesoporous silica (Ni2P@mSiO2). The Ni2P@mSiO2 nanocatalysts were characterized by a range of techniques including CO chemisorption to determine active site densities and sulfur analysis to determine the S content following HDS measurements and treatment in a mixture of H2S/H2. The extent of sulfur deactivation depended strongly on Ni2P particle size, with Ni2P@mSiO2-5.9 nm showing no change in HDS turnover frequency (TOF) before and after co-feeding H2S, while Ni2P@mSiO2-17.1 nm exhibited a significant decrease in HDS activity and TOF after co-feeding H2S. The composition of the surface phosphosulfide layer formed on the Ni2P nanoparticles also changed with particle size, with the surface S/Ni ratio increasing as the particle size increased. Further insights into how Ni2P particle size affects sulfur deactivation will be presented, as well as the ramifications for deep HDS processing over Ni2P-based catalysts.

Probing the effect of particle size on sulfur deactivation of nickel phosphide hydrotreating catalysts

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