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

The size-dependent catalytic activity of Ni2P for hydrodesulfurization (HDS) remains unstudied because the traditional temperature programmed reduction (TPR) method used in catalyst preparation results in highly polydisperse Ni2P particles. The ability to control the Ni2P 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 degrees C. Sintering is minimized by encapsulation of Ni2P nanoparticles in a mesoporous silica shell, achieved by sol-gel silica formation around Ni2P-containing surfactant liquid crystal assemblies and subsequent calcination, resulting in a doubling of HDS activity.