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Arrangements of identical hard spheres confined to a cylinder with hard walls have been used to model experimental systems, such as fullerenes in nanotubes and colloidal wire assembly. Finding the densest configurations, called close packings, of hard spheres of diameter σ in a cylinder of diameter D is a purely geometric problem that grows increasingly complex as D/σ increases, and little is thus known about the regime for D > 2.873σ. In this work, we extend the identification of close packings up to D = 4.00σ by adapting Torquato-Jiao's adaptive-shrinking-cell formulation and sequential-linear-programming (SLP) technique. We identify 17 new structures, almost all of them chiral. Beyond D ≈ 2.85σ, most of the structures consist of an outer shell and an inner core that compete for being close packed. In some cases, the shell adopts its own maximum density configuration, and the stacking of core spheres within it is quasiperiodic. In other cases, an interplay between the two components is observed, which may result in simple periodic structures. In yet other cases, the very distinction between the core and shell vanishes, resulting in more exotic packing geometries, including some that are three-dimensional extensions of structures obtained from packing hard disks in a circle.

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Biodiesel combustion models demand detailed understanding of the reactions undertaken by the ester functional group in the molecule. Investigations of the chemistry of small methyl esters can contribute to this goal. We have thus chosen methyl propanonate (MP) as a representative ester molecule in a study combining theory, model, and experiments. As an advantage, its reactions are also amenable to high-level theoretical calculations. Based on recent theoretical calculations , a new kinetics model for small ester combustion was developed and validated. New experimental results were obtained here in an extensive range of conditions, including full speciation in laminar low-pressure flames at two different stoichiometries ( φ = 0.8 and 1.5) using electron ionization (EI) molecular-beam mass spectrometry (MBMS) and flame speed measurements in a spherical confined chamber (1-6 atm). Comparison of the experimental data to the present model shows overall improved performance. Some specific new reaction pathways to form methanol, methylketene, methyl acetate, and acetic acid from the fuel radicals were identified and will permit more detailed insights into the combustion properties of methyl propanoate.

Ammonia synthesis at 533 K and atmospheric pressure was investigated in a coaxial dielectric barrier discharge (DBD) plasma reactor without packing and with porous γ-Al2O3, 5 wt % Ru/γ-Al2O3, or 5 wt % Co/γ-Al2O3 catalyst particles. Gas-phase species were monitored in situ using an electron impact molecular-beam mass spectrometer (EI-MBMS). Gas-phase species NNH and N2H2 were first identified under common conditions of plasma-assisted ammonia synthesis and were present at levels comparable to that of NH3 in the plasma discharge. Concentrations of NNH, N2H2, and NH in a reactor packed with γ-Al2O3 or other particles were lower than those observed in an empty reactor, while the concentration of NH3 increased. These observations point to the importance of NNH and N2H2 in plasma-assisted surface reactions in ammonia synthesis. Reaction pathways of direct adsorption of gas-phase NNH and N2H2 on solid surfaces and subsequent reactions were proposed. This study demonstrated that in situ identification of gas-phase species via EI-MBMS provides a powerful approach to study the kinetics of plasma-assisted catalysis.

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TiO2-modified oxygen-functionalized activated carbon (TiO2@OAC)-loaded nickel-based catalysts (Ni/TiO2@OAC) were synthesized and applied in the hydrogenation of chloronitrobenzene (CNB) to chloroanilines (CANs). The characterization results indicate that introduction of TiO2 restrains nickel nanoparticles sintering and improves the stability of the catalysts by strong metal–support interaction. Additionally, the X-ray photoelectron spectroscopy results suggest that the electron donating effect of Ti3+ produces electron-rich Ni (Niδ−), which inhibits C–Cl moiety adsorption. The formed Niδ− species might induce electron-rich hydrogen (H–) generation which facilitates a nucleophilic attack on −NO2 rather than an electrophilic attack on the C–Cl bond. Furthermore, the electron-donating ability of −NH2 could be reduced because of the interaction between −OH in TiO2@OAC and −NH2 in CAN. Hence, the dechlorination is inhibited and the selectivity to m-CAN is up to 99.0%. The catalytic performance of Ni/TiO2@OAC could be maintained after five cycles.