Nickel phosphide nanoparticles encapsulated in mesoporous silica (Ni2P@mSiO(2)) were used to probe particle size effects in the deep hydrodesulfurization (HDS) of 4,6-dimethyldibenzothiophene, (4,6-DMDBT). The HDS properties of the well-defined nanoparticle catalysts were compared to those of Ni2P/SiO2 catalysts prepared by different methods and having different particle sizes. The Ni-2 PpmSiO(2) nanocatalysts had Ni2P particle sizes of 6.3, 11.4, and 16.0 nm, while the Ni2P/SiO2 catalysts had particle sizes of 3.2 and 5.7 nm. Linear correlations of CO chemisorption capacity and 4,6-DMDBT HDS activity with calculated Ni2P surface area were observed for the Ni2P@mSiO(2) nanocatalysts. The CO chemisorption measurements yield a value of 0.28 CO molecules per surface Ni atom, with some Ni sites likely blocked by the mesoporous silica shell that encapsulates Ni2P nanoparticles, as well as possibly by excess P at the particle surfaces. HDS turnover frequencies (TOFs), normalized on the basis of surface Ni sites and CO chemisorption, yield values of (1.1-2.1) x 10(-5) s(-1) (TOFNi) and (4.7-8.4) x 10(-5) s(-1) (TOFCO) for the Ni2P@mSiO(2) nanocatalysts at a reaction temperature of 553 K. The TOFNi values are similar to or higher than those measured for the Ni2P/SiO2 catalysts. With respect to sites titrated by CO (TOFCO), theNi(2)P/SiO2 catalyst prepared from a hypophosphite-based precursor was over two times more active than the Ni2P@mSiO(2) nanocatalysts and the Ni2P/SiO2 catalyst prepared from a phosphate-based precursor. The Ni2P@mSiO(2) nanocatalyst having 6.3 nm Ni2P nanoparticles and the Ni2P/SiO2-hypo catalyst had higher HDS activities than a commercial sulfided Ni-Mo/Al2O3 catalyst; the results indicate that a catalyst composed of 3-5 nm Ni2P particles would have a 4,6-DMDBT HDS activity competitive with commercial Co-Mo/Al2O3 and Ni-Mo/Al2O3 catalysts. The Ni2P@mSiO(2) and Ni2P/SiO2 catalysts strongly favored products of the hydrogenation pathway for sulfur removal as did the sulfided Ni-Mo/Al2O3 catalyst.

An in situ method for the preparation of nickel phosphide (Ni2P) on silica, alumina, and amorphous silica alumina (ASA) supports is described. The synthesis avoids the use of nickel and phosphorus salts by employing the reaction between nickel hydroxide (Ni(OH)(2)) and hypophosphorus acid (H3PO2), allowing the impregnation of nickel hypophosphite (Ni(H2PO2)(2)) onto the oxide supports in the absence of salt by-products. Temperature-programmed reduction (TPR) in flowing hydrogen at 573-773 K yields phase pure Ni2P on the supports with small average particle sizes (3-4 nm) as measured using transmission electron microscopy. The conversion of Ni(H2PO2)(2) to Ni2P and related reactions were probed using TPR with on-line mass spectral analysis of the gas effluent. Unsupported Ni(H2PO2)(2) reacts in flowing hydrogen to produce PH3 and H2O at 468 and 482 K, respectively; the reaction is shifted to increasingly higher temperatures for Ni(H2PO2)(2) supported on SiO2, Al2O3 and ASA. The hydrodenitrogenation (HDN) and hydrodesulfurization (HDS) properties of the Ni2P catalysts were probed using a mixed feed containing carbazole and benzothiophene. While Ni2P/SiO2 catalysts prepared by the different methods exhibited similar HDN and HDS activities, the in situ prepared Ni2P/Al2O3 and Ni2P/ASA catalysts were substantially more active than their ex situ counterparts prepared from hypophosphite- and phosphate-based precursors. (C) 2015 Elsevier Inc. All rights reserved.

Metal phosphide nanoparticles encapsulated in mesoporous silica provide a well-defined system for probing the fundamental chemistry of the hydrodesulfurization (HDS) reaction over this new class of hydrotreating catalysts. To investigate composition effects in bimetallic phosphides, the HDS of dibenzothiophene (DBT) was carried out over a series of Ni-rich Ni2-xMxP@mSiO(2) (M = Co, Fe) nanocatalysts (x <= 0.50). The Ni2-xMxP nanoparticles (average diameters: 11-13 nm) were prepared by solution-phase arrested precipitation and encapsulated in mesoporous silica, characterized by a range of techniques (XRD, TEM, IR spectroscopy, BET surface area, CO chemisorption) and tested for DBT HDS activity and selectivity. The highest activity was observed for a Ni1.92Co0.08P@mSiO(2) nanocatalyst, but the overall trend was a decrease in HDS activity with increasing Co or Fe content. In contrast, the highest turnover frequency (TOF) was observed for the most Co- and Fe-rich compositions based on sites titrated by CO chemisorption. IR spectral studies of adsorbed CO on the Ni2-xMxP@mSiO(2) catalysts indicate that an increase in electron density occurs on Ni sites as the Co or Fe content is increased, which may be responsible for the increased TOFs of the catalytic sites. The Ni2-xMxP@mSiO(2) nanocatalysts exhibit a strong preference for the direct desulfurization pathway (DDS) for DBT HDS that changes only slightly with increasing Co or Fe content. (C) 2015 Elsevier B.V. All rights reserved.

A synthetic protocol developed to produce phase-pure, nearly monodisperse Ni2–xCoxP nanoparticles (x ≤ 1.7) is described. The Ni2–xCoxP particles vary in size, ranging from 9–14 nm with standard deviations of <20% (based on transmission electron microscopy analysis), and the actual metal ratios obtained from energy-dispersive spectroscopy closely follow the targeted ratios. With increasing Co, samples with larger size distributions are obtained and include particles with voids, attributed to the Kirkendall effect. To probe the mechanism of ternary phosphide particle formation, detailed studies were conducted for Ni:Co = 1:1 as a representative composition. It was revealed that the P:M ratio, heating temperature, and heating time have a large impact on the nature of both intermediate and final crystalline particles formed. By tuning these conditions, nanoparticles can be produced with different sizes (from ca. 7–25 nm) and morphologies (hollow versus dense).