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.

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The synthesis of monodisperse 5-10 nm Pd5P2 catalytic particles by encapsulation in a mesoporous silica network, along with preliminary data on hydrodesulfurization (HDS) activity, is reported. Precursor Pd-P amorphous nanoparticles are prepared by solution-phase reaction of palladium(II) acetylacetonate with trioctylphosphine at temperatures up to 300 °C. Direct crystallization of Pd5P2 in solution by increasing the temperature to 360 °C leads to sintering, but particle size can be maintained during the transformation by encapsulation of the amorphous Pd-P particles in a mesoporous silica shell, followed by treatment of the solid at 500 °C under a reducing atmosphere, yielding Pd5P2@mSiO2. The resultant materials exhibit high BET surface areas (>1000 m(2)/g) and an average pore size of 3.7 nm. Access to the catalyst surface is demonstrated by dibenzodithiophene (DBT) HDS testing. Pd5P2@mSiO2 shows a consistent increase in HDS activity as a function of temperature, with DBT conversion approaching 60% at 402 °C. The ability to control particle size, phase, and sintering is expected to enable the fundamental catalytic attributes that underscore activity in Pd5P2 to be assessed.

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