Explore the vast range of titles available.

The propagation speeds of premixed n-butane–air mixtures (2.0–5.7 vol%) were investigated under various initial conditions (pressures of 0.4–1.2 bar; temperatures of 289–500 K). The study consists of both, experimental measurements using two different enclosures (a sphere and a cylinder) and kinetic modeling via a dedicated computing program. The propagation speeds of premixed n-butane–air mixtures were obtained via the adiabatic model of flame propagation, which allows us to obtain these important parameters using the normal burning velocities and expansion coefficients. The expansion coefficients were calculated using thermodynamic data as the ratio of burnt to unburnt gas densities, assuming that an equilibrium was established in the flame front. The propagation speeds obtained based on the experimental burning velocities were analyzed for comparison with the computed velocities. Finally, the dependence of the propagation speed on the initial pressure and temperature was discussed.

The absence of catalytic asymmetric methods for synthesizing chiral (hetero)bicyclo[n.1.1]alkanes has hindered their application in new drug discovery. Here we demonstrate the achievability of an asymmetric polar cycloaddition of bicyclo[1.1.0]butane using a chiral Lewis acid catalyst and a bidentate chelating bicyclo[1.1.0]butane substrate, as exemplified by the current enantioselective formal (3 + 3) cycloaddition of bicyclo[1.1.0]butanes with nitrones. In addition to the diverse bicyclo[1.1.0]butanes incorporating an acyl imidazole group or an acyl pyrazole moiety, a wide array of nitrones are compatible with this Lewis acid catalysis, successfully assembling two congested quaternary carbon centers and a chiral aza-trisubstituted carbon center in the pharmaceutically important hetero-bicyclo[3.1.1]heptane product with up to 99% yield and >99% ee . The absence of catalytic asymmetric methods for synthesizing chiral (hetero)bicyclo[n.1.1]alkanes has hindered their application in new drug discovery. Herein the authors report an enantioselective formal (3 + 3) cycloaddition of bicyclobutanes with nitrones using a chiral Lewis acid catalyst for the synthesis of hetero-bicyclo[3.1.1]heptane.

The present work deals with the development of Co[sub.3]O[sub.4]-based catalysts for potential application in catalytic gas sensors for methane (CH[sub.4]) detection. Among the transition-metal oxide catalysts, Co[sub.3]O[sub.4] exhibits the highest activity in catalytic combustion. Doping Co[sub.3]O[sub.4] with another metal can further improve its catalytic performance. Despite their promising properties, Co[sub.3]O[sub.4] materials have rarely been tested for use in catalytic gas sensors. In our study, the influence of catalyst morphology and Ni doping on the catalytic activity and thermal stability of Co[sub.3]O[sub.4]-based catalysts was analyzed by differential calorimetry by measuring the thermal response to 1% CH[sub.4]. The morphology of two Co[sub.3]O[sub.4] catalysts and two Ni[sub.x]Co[sub.3−x]O[sub.4] with a Ni:Co molar ratio of 1:2 and 1:5 was studied using scanning transmission electron microscopy and energy dispersive X-ray analysis. The catalysts were synthesized by (co)precipitation with KOH solution. The investigations showed that Ni doping can improve the catalytic activity of Co[sub.3]O[sub.4] catalysts. The thermal response of Ni-doped catalysts was increased by more than 20% at 400 °C and 450 °C compared to one of the studied Co[sub.3]O[sub.4] oxides. However, the thermal response of the other Co[sub.3]O[sub.4] was even higher than that of Ni[sub.x]Co[sub.3−x]O[sub.4] catalysts (8% at 400 °C). Furthermore, the modification of Co[sub.3]O[sub.4] with Ni simultaneously brings stability problems at higher operating temperatures (≥400 °C) due to the observed inhomogeneous Ni distribution in the structure of Ni[sub.x]Co[sub.3−x]O[sub.4]. In particular, the Ni[sub.x]Co[sub.3−x]O[sub.4] with high Ni content (Ni:Co ratio 1:2) showed apparent NiO separation and thus a strong decrease in thermal response of 8% after 24 h of heat treatment at 400 °C. The reaction of the Co[sub.3]O[sub.4] catalysts remained quite stable. Therefore, controlling the structure and morphology of Co[sub.3]O[sub.4] achieved more promising results, demonstrating its applicability as a catalyst for gas sensing.

In this work, we report the temperature-dependent solid-state photoluminescence properties of the phosphine-supported copper(I) - halide dinuclear complexes, [(bdpb)CuX].sub.2 (bdpb = 1,4-bis(diphenyl-phosphaneyl)butane, X = I, 1; Br, 2; Cl, 3). The X-ray diffraction analyses reveal that the metal centers exhibit a distorted tetrahedral structure in three complexes, wherein the dinuclear centers are separated via two bridging halide anions with the long CuâCu distances [3.109(2) Å for 1, 3.200(2) Å for 2 and 3.181(2) Å for 3] in the X-ray structure. The luminescence properties of the three compounds were investigated in detail as a function of the temperature showing reversible luminescence thermochromism with an intense blue emission at low temperature.

Raman spectroscopy is a promising method for the analysis of natural gas. It is necessary to account for the broadening effects on spectral lines to improve measurement accuracy. In this study, the broadening coefficients for methane lines in the region of the ν[sub.2] band perturbed by propane, n-butane, and isobutane at room temperature were measured. We estimated the measurement errors of the concentration of oxygen and carbon dioxide in the case of neglecting the broadening effects on the methane spectrum by the pressure of C[sub.2]–C[sub.6] alkanes. The obtained data are suited for the correct simulation of the methane spectrum in the hydrocarbon-bearing gases and can be used to improve the accuracy of the analysis of natural gas by Raman spectroscopy.

Ceramic aerogels are highly efficient, lightweight, and chemically stable thermal insulation materials but their application is hindered by their brittleness and low strength. Flexible nanostructure-assembled compressible aerogels have been developed to overcome the brittleness but they still show low strength, leading to insufficient load-bearing capacity. Here we designed and fabricated a laminated SiC-SiO x nanowire aerogel that exhibits reversible compressibility, recoverable buckling deformation, ductile tensile deformation, and simultaneous high strength of up to an order of magnitude larger than other ceramic aerogels. The aerogel also shows good thermal stability ranging from −196 °C in liquid nitrogen to above 1200 °C in butane blow torch, and good thermal insulation performance with a thermal conductivity of 39.3 ± 0.4 mW m −1 K −1 . These integrated properties make the aerogel a promising candidate for mechanically robust and highly efficient flexible thermal insulation materials. Mechanically robust, flexible and thermally insulating ceramic aerogels are challenging to obtain due to the conflicting nature of these properties. Here the authors resolved these contradictions and developed a strong yet flexible aerogel, for application in extreme conditions, by laminated structure design.

The Deepwater Horizon (DWH) oil spill in the spring of 2010 resulted in an input of ∼4.1 million barrels of oil to the Gulf of Mexico; >22% of this oil is unaccounted for, with unknown environmental consequences. Here we investigated the impact of oil deposition on microbial communities in surface sediments collected at 64 sites by targeted sequencing of 16S rRNA genes, shotgun metagenomic sequencing of 14 of these samples and mineralization experiments using 14 C-labeled model substrates. The 16S rRNA gene data indicated that the most heavily oil-impacted sediments were enriched in an uncultured Gammaproteobacterium and a Colwellia species, both of which were highly similar to sequences in the DWH deep-sea hydrocarbon plume. The primary drivers in structuring the microbial community were nitrogen and hydrocarbons. Annotation of unassembled metagenomic data revealed the most abundant hydrocarbon degradation pathway encoded genes involved in degrading aliphatic and simple aromatics via butane monooxygenase. The activity of key hydrocarbon degradation pathways by sediment microbes was confirmed by determining the mineralization of 14 C-labeled model substrates in the following order: propylene glycol, dodecane, toluene and phenanthrene. Further, analysis of metagenomic sequence data revealed an increase in abundance of genes involved in denitrification pathways in samples that exceeded the Environmental Protection Agency (EPA)’s benchmarks for polycyclic aromatic hydrocarbons (PAHs) compared with those that did not. Importantly, these data demonstrate that the indigenous sediment microbiota contributed an important ecosystem service for remediation of oil in the Gulf. However, PAHs were more recalcitrant to degradation, and their persistence could have deleterious impacts on the sediment ecosystem.

Recently, global warming is proving to be an increasing challenge for the sustainable human survival on planet earth. Worldwide, researchers are putting their efforts into controlling carbon emissions and have set the aim to achieve levels of overall carbon neutrality. Different industrial processes, especially oil refinery processes, release large amounts of low-carbon alkanes as gaseous byproducts directly into the air and pollute clean environments, which is one of the major reasons for sudden climate changes, ocean acidification, loss of biodiversity, and rising sea levels. The conversion of lighter alkanes, especially n-butane, into value-added chemicals can be beneficial for green economies and green environments. Presently, heterogeneous vanadium phosphorus oxide catalysts (VPOs) are considered potential candidates for n-butane selective oxidation toward maleic anhydride (MA). In this research, we developed a VPO catalyst with the assistance of copper-based ionic liquids (Cu-ILs), including [Bmim][OAc]–[Cu(OAc)2], [Bmim][Cl]–[CuCl], and [Bmim][Cl]–[CuCl2]. We observed significant improvement in the MA selectivity; meanwhile, the COx (CO and CO2) selectivity was decreased. Compared to the unpromoted catalyst (Blank-VPO), the Cu-IL-promoted catalyst, i.e., [Bmim][Cl]–[CuCl2]-VPO remarkably increased the MA selectivity (11%) and n-butane conversion (9.2%) and minimized the COx selectivity (11%). In addition to this the ratio of CO/CO2 has been reduced from 2.01 to 1.32. Therefore, this can be a helpful process for achieving carbon neutrality goals.

The recent availability of shale gas has led to a renewed interest in C-H bond activation as the first step towards the synthesis of fuels and fine chemicals. Heterogeneous catalysts based on Ni and Pt can perform this chemistry, but deactivate easily due to coke formation. Cu-based catalysts are not practical due to high C-H activation barriers, but their weaker binding to adsorbates offers resilience to coking. Using Pt/Cu single-atom alloys (SAAs), we examine C-H activation in a number of systems including methyl groups, methane and butane using a combination of simulations, surface science and catalysis studies. We find that Pt/Cu SAAs activate C-H bonds more efficiently than Cu, are stable for days under realistic operating conditions, and avoid the problem of coking typically encountered with Pt. Pt/Cu SAAs therefore offer a new approach to coke-resistant C-H activation chemistry, with the added economic benefit that the precious metal is diluted at the atomic limit.