11 Search Results

Oxidative dehydrogenation of propane (ODHP) to propylene could have a significant impact on the production of this critical chemical intermediate, if appropriate catalysts can be discovered. Recently, heterogeneous catalysts based on boron (oxides and nitrides) have been demonstrated to be promising for ODHP, but their active sites have not been conclusively identified. Here, we report that the deposition of differently sized boronic acids into the micropores of silica supports results in different distributions of surface borate species after calcination. Furthermore, these materials, in turn, display a wide range of rates in ODHP but similar selectivity, suggesting that they differ onlymore » in the numbers of active sites. Features identified by in situ Raman, IR, and magic-angle-spinning ¹¹B solid-state NMR spectroscopies are compared to catalyst activity. This correlation identifies the S2 borate species, a hydroxylated nonring boron, as the likely active site and provides a target for directed syntheses of future catalysts.« less

Tandem catalysis couples multiple reactions and promises to improve chemical processing, but precise spatiotemporal control over reactive intermediates remains elusive. We used atomic layer deposition to grow In ₂ O ₃ over Pt/Al ₂ O ₃ , and this nanostructure kinetically couples the domains through surface hydrogen atom transfer, resulting in propane dehydrogenation (PDH) to propylene by platinum, then selective hydrogen combustion by In ₂ O ₃ , without excessive hydrocarbon combustion. Other nanostructures, including platinum on In ₂ O ₃ or platinum mixed with In ₂ O ₃ , favor propane combustion because they cannot organize the reactions sequentially.more » The net effect is rapid and stable oxidative dehydrogenation of propane at high per-pass yields exceeding the PDH equilibrium. Tandem catalysis using this nanoscale overcoating geometry is validated as an opportunity for highly selective catalytic performance in a grand challenge reaction.« less

The microstructure of EBR-II neutron-irradiated austenitic stainless steel 304 and nickel-base alloy X-750 was investigated. Both alloys were irradiated at low dose rates (~2 × 10^-8 dpa/s) to a neutron fluence of 6.9 × 10²² n/cm² (E > 0.1 MeV) at 371–389 °C. Different types of defects, including Frank loops, cavities, and γ' precipitates were characterized. The Frank loops in Type 304 stainless steel (SS) are larger in size (~50 nm in diameter) and lower in number density (2.58 × 10²¹ m^-3), compared to most previous higher dose rate neutron irradiation studies. The Frank loops in X-750 have an averagemore » size 26.0 nm of and a number density of 9.44 × 10²¹ m^-3. In 304 SS and X-750, cavities are of ~20 nm and ~14 nm in diameter, respectively. The swelling of both alloys was found to be insignificant. In 304 SS, Ni and Si were found enriched at the cavity surfaces and Ni,Si-rich precipitates were also found. Multivariate statistical analysis using non-negative matrix factorization reveals that these Ni,Si-rich precipitates contain only ~5.7 at.% Si, differing from the Ni₃Si γ' precipitates found in several previous studies. In X-750, L1₂-structured γ' precipitates were found, and multivariate statistical analysis confirmed the 3:1 stoichiometry (Ni₃(Ti,Al)) of the precipitates and the superlattice reflections confirmed the stability of the crystal structure of these γ' precipitates, indicating higher-than-expected precipitate stability under high-dose neutron irradiation.« less

Unprotected E-hydrazone esters are prized building blocks for the preparation of 1H-indazoles and countless other N-containing biologically active molecules. Despite previous advances, efficient and stereoselective synthesis of these compounds remains nontrivial. Here, we show that Pt single atoms anchored on defect-rich CeO₂ nanorods (Pt₁/CeO₂), in conjunction with the alcoholysis of ammonia borane, promotes exceptionally E-selective hydrogenation of α-diazoesters to afford a wide assortment of N-H hydrazone esters with an overall turnover frequency of up to 566 hours^-1 upon reaction completion. The α-diazoester substrates could be generated in situ from readily available carboxylic esters in one-pot hydrogenation reaction. Utility is demonstratedmore » through concise, scalable synthesis of 1H-indazole–derived pharmaceuticals and their ¹⁵N-labeled analogs. The present protocol highlights a key mechanistic nuance wherein simultaneous coordination of a Pt site with the diazo N=N and ester carbonyl motifs plays a central role in controlling stereoselectivity, which is supported by density functional theory calculations.« less

Fluid-feeding insects, such as butterflies, moths, and flies (20% of all animal species), are faced with the common selection pressure of having to remove and feed on trace amounts of fluids from porous surfaces. Insects able to acquire fluids that are confined to pores during drought conditions would have an adaptive advantage and increased fitness over other individuals. Here we performed feeding trials using solutions with magnetic nanoparticles to show that butterflies and flies have mouthparts adapted to pull liquids from porous surfaces using capillary action as the governing principle. In addition, the ability to feed on the liquids collectedmore » from pores depends on a relationship between the diameter of the mouthpart conduits and substrate pore size diameter; insects with mouthpart conduit diameters larger than the pores cannot successfully feed, thus there is a limiting substrate pore size from which each species can acquire liquids for fluid uptake. In conclusion, given that natural selection independently favored mouthpart architectures that support these methods of fluid uptake (Diptera and Lepidoptera share a common ancestor 280 mya that had chewing mouthparts), we suggest that the convergence of this mechanism advocates this as an optimal strategy for pulling trace amounts of fluids from porous surfaces.« less

The field-driven magnetization dynamics of a multiskyrmion cluster in a nanodisk is investigated by micromagnetic simulation and analytical calculation. Under a weak in-plane static magnetic field, the multiskyrmion cluster shows an oscillatory motion around an equilibrium position, which resembles the dynamical behavior of the conventional torsional pendulum. We show that this oscillation is induced by restoring torque acting on the skyrmion generated by the potential energy determined by the angle of the skyrmion orientation. Moreover, the multiskyrmion cluster can be driven to rotate by an in-plane rotating magnetic field. The rotation directions and frequencies are fully determined by the numbermore » of the skyrmions.« less