A synthetic protocol developed to produce phase-pure, nearly monodisperse Ni 2-x Co x P nanoparticles (x≤1.7) is described. The Ni 2-x Co x P particles vary in size, ranging from 9-14 nm with standard deviations of <20% (based on TEM analysis) and the actual metal ratios obtained from EDS 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. In order 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 morphol0gy (hollow vs. dense).

An in situ method for the preparation of nickel phosphide (Ni 2 P) 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 hyphosphorus acid (H 3 PO 2), allowing the impregnation of nickel hypophosphite (Ni(H 2 PO 2) 2) onto the oxide supports in the absence of salt byproducts. Temperature-programmed reduction (TPR) in flowing hydrogen at 573-773 K yields phase pure Ni 2 P on the supports with small average particle sizes (3-4 nm) as measured using transmission electron microscopy. The conversion of Ni(H 2 PO 2) 2 to Ni 2 P and related reactions were probed using TPR with on-line mass spectral analysis of the gas effluent. Unsupported Ni(H 2 PO 2) 2 reacts in flowing hydrogen to produce PH 3 and H 2 O at 468 and 482 K, respectively; the reaction is shifted to increasingly higher temperatures for Ni(H 2 PO 2) 2 supported on SiO 2 , Al 2 O 3 and ASA. The hydrodenitrogenation (HDN) and hydrodesulfurization (HDS) properties of the Ni 2 P catalysts were probed using a mixed feed containing carbazole and benzothiophene. While Ni 2 P/SiO 2 catalysts prepared by the different methods exhibited similar HDN and HDS activities, the in situ prepared Ni 2 P/Al 2 O 3 and Ni 2 P/ASA catalysts were substantially more active than their ex situ counterparts prepared from hypophosphite-and phosphate-based precursors.

We have measured several IR bands of FCH2CN-BF3 and ClCH2CN-BF3 in solid nitrogen, argon, and neon. These bands include the B-F asymmetric stretch (νBF(a)), the B-F symmetric stretch (νBF(s)), the BF3 symmetric deformation or "umbrella" mode (δBF(s)), and the CN stretch (νCN). For both complexes, the frequencies of these modes shift across the various media, particularly the B-F asymmetric stretching band, and thus they indicate that the inert gas matrix environments significantly alter the structural properties of FCH2CN-BF3 and ClCH2CN-BF3. Furthermore, the frequencies shift in a manner that parallels the dielectric constant of these media, which suggests a progressive contraction of the B-N distances in these systems and also that it parallels the ability of the medium to stabilize the increase in polarity that accompanies the bond contraction. We have also mapped the B-N distance potentials for FCH2CN-BF3 and ClCH2CN-BF3 using several density functional and post-Hartree-Fock methods, all of which reveal a flat, shelflike region that extends from the gas-phase minimum (near 2.4 Å) toward the inner wall (to about 1.7 Å). Furthermore, we were able to rationalize the medium effects on the structure by constructing hybrid bond potentials composed of the electrostatic component of the solvation free energy and the gas-phase electronic energy. These curves indicate that the solvation energies are greatest at short B-N distances (at which the complex is more polar), and ultimately, the potential minima shift inward as the dielectric constant of the medium increases.

We have conducted an extensive computational study of the structural and energetic properties of select acetonitrile-Group IV (A & B) tetrahalide complexes, both CH3CN-MX4 and (CH3CN)2-MX4 (M = Si, Ge, Ti; X = F, Cl). We have also examined the reactivity of CH3CN with SiF4, SiCl4, GeCl4, and TiCl4, and measured low-temperature IR spectra of thin films containing CH3CN with SiF4, GeCl4, or TiCl4. The six 1:1 complexes fall into two general structural classes. CH3CN-TiCl4, CH3CN-TiF4, and CH3CN-GeF4, exhibit relatively short M-N bonds (~2.3 Å), an intermediate degree of distortion in the MX4 subunit, and binding energies ranging from 11.0 to 13.0 kcal/mol. Conversely, CH3CN-GeCl4, CH3CN-SiF4, and CH3CN-SiCl4, are weakly bonded systems, with long M-N distances (>3.0 Å), little distortion in the MX4 subunit, and binding energies ranging from 3.0 to 4.4 kcal/mol. The structural features of analogous 2:1 systems resemble those of their 1:1 counterparts, whereas the binding energies (relative to three isolated fragments) are roughly twice as large. Calculated M-N potential curves in the gas phase and bulk, dielectric media are reported for all 1:1 complexes, and for two systems, CH3CN-GeF4 and CH3CN-SiF4, these data predict significant condensed-phase structural changes. The effect on the CH3CN-SiF4 potential is extreme; the curve becomes quite flat over a broad range in dielectric media, and at higher ε values, the global minimum shifts inward by about 1.0 Å. In bulk reactivity experiments, no reaction was observed between CH3CN and SiF4, SiCl4, or GeCl4, whereas CH3CN and TiCl4 were found to react immediately upon contact. Also, thin-film IR spectra indicate a strong interaction between CH3CN and TiCl4, yet only weak interactions between CH3CN and GeCl4 or SiF4 in the solid state.

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Nickel phosphide nanoparticles encapsulated in mesoporous silica (Ni2P@mSiO2) 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 Ni2P@mSiO2 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@mSiO2 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) × 10–5 s–1 (TOFNi) and (4.7–8.4) × 10–5 s–1 (TOFCO) for the Ni2P@mSiO2 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), the Ni2P/SiO2 catalyst prepared from a hypophosphite-based precursor was over two times more active than the Ni2P@mSiO2 nanocatalysts and the Ni2P/SiO2 catalyst prepared from a phosphate-based precursor. The Ni2P@mSiO2 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@mSiO2 and Ni2P/SiO2 catalysts strongly favored products of the hydrogenation pathway for sulfur removal as did the sulfided Ni–Mo/Al2O3 catalyst.

The FCHCN-BCl and ClCHCN-BCl complexes were investigated by quantum-chemical computations and low-temperature, matrix-isolation-IR spectroscopy. Theory predicts two stable equilibrium structures, with distinctly different B-N distances, for both complexes. One set of structures, which correspond to the global energy minima, exhibit B-N distances of 1.610 and 1.604 Å for FCHCN-BCl and ClCHCN-BCl, respectively (via M06-2X/aug-cc-pVTZ). The corresponding binding energies are 5.3 and 6.3 kcal/mol. For the metastable structures, the B-N distances are 2.870 and 2.865 Å for FCHCN-BCl and ClCHCN-BCl, respectively, and the corresponding binding energies are 3.2 and 3.3 kcal/mol. Also, the barriers between these structures on the B-N distance potentials are 2.5 and 2.8 kcal/mol, respectively, relative to the secondary, long-bond minima. In addition, several IR bands of both FCHCN-BCl and ClCHCN-BCl were observed in nitrogen matrices, but the assigned bands are consistent with M06-2X predictions for the short-bond, minimum-energy structures. None of the observed IR bands could be assigned to the metastable, long-bond structures.

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