Rational Design of Nickel Phosphide Hydrodesulfurization Catalysts: Controlling Particle Size and Preventing Sintering

The size-dependent catalytic activity of Ni 2 P for hydrodesulfurization (HDS) remains unstudied because the traditional temperature programmed reduction (TPR) method used in catalyst preparation results in highly polydisperse Ni 2 P particles. The ability to control the Ni 2 P particle size in the range 5–20 nm by varying the quantity of oleylamine in solution-phase arrested precipitation reactions is reported. Particles were introduced to a high surface area silica support (Cab-O-Sil, M-7D grade, 200 m 2 /g) via incipient wetness, and HDS activity was probed against dibenzothiophene (DBT). All samples were less active than TPR prepared materials, and the smallest particles were the least active, contrary to expectation. This is attributed in part to particle sintering under HDS conditions. Sintering occurs independently of wt% loading of catalyst, time, incipient wetness procedure, and ionic additives, at all temperatures greater than 200 °C. Sintering is minimized by encapsulation of Ni 2 P nanoparticles in a mesoporous silica shell, achieved by sol–gel silica formation around Ni 2 P-containing surfactant liquid crystal assemblies and subsequent calcination, resulting in a doubling of HDS activity.