Highly Efficient Metal Sulfide Catalysts for Selective Dehydrogenation of Isobutane to Isobutene

Metal sulfide catalysts were highly efficient in the activation of C–H bond for isobutane dehydrogenation, and the dehydrogenation performance was better than that of the commercial catalysts Cr₂O₃/Al₂O₃ and Pt–Sn/Al₂O₃, providing a class of environmentally friendly and economical alternative catalysts for industrial application

Synthesis of Thermal Degradable Poly(alkoxyamine) through a Novel Nitroxide Radical Coupling Step Growth Polymerization Mechanism

The thermal degradable poly­(alkoxyamine) was synthesized through a novel nitroxide radical coupling step growth polymerization (NRC-SGP) mechanism. The monomers of 1,4-phenylene bis­(2-bromo-2-methylpropanoate) (monomer <b>1</b>) and 1,4-phenylene bis­(2-bromopropanoate) (monomer <b>1</b>′) with two bromide groups and 1,6-di­(4-(2,2,6,6-tetramethylpiperidine-1-oxyl))-hexa-2,4-diyne (monomer <b>2</b>) with two nitroxide radicals were first designed and synthesized. Then the NRC-SGP mechanism was investigated in detail by optimizing the factors such as polymerization time, temperature, solvents, catalysts, ligand, monomer concentration, and structures connected to halogen groups. The results showed that the termination by disproportionation was the major side reaction in the NRC-SGP mechanism, and the lower temperature (25 °C) would favor an important contribution. The proper combination of all factors could lead to an ideal NRC-SGP procedure. Finally, the thermal stability of formed poly­(alkoxyamine) was monitored by TG, DSC and SEC instruments, and the results showed that the poly­(alkoxyamine) would suffer a severe thermal degradation at the elevated temperature above 140 °C

Effect of Sn on Isobutane Dehydrogenation Performance of Ni/SiO₂ Catalyst: Adsorption Modes and Adsorption Energies of Isobutane and Isobutene

The reaction of isobutane over Ni/SiO₂ catalyst changes from hydrogenolysis to dehydrogenation when Sn is introduced. The adsorption modes and energies of isobutane and isobutene over the Ni/SiO₂ catalyst with and without Sn addition were determined by in situ FTIR and a novel transient response adsorption approach. In the absence of Sn, isobutane is adsorbed in a double-site mode with H atoms in two methyl groups of isobutane, facilitating hydrogenolysis of isobutane. After the addition of Sn, a single-site adsorption mode with the H atom in the methylidyne group is speculated instead, which is beneficial to the rupture of the C–H bond rather than the C–C bond. Moreover, the double-site adsorption mode of isobutene with the CC bond and the H atom in a methyl group is turned into single-site mode with the CC bond after the introduction of Sn. As for the adsorption energy of isobutene, the introduction of Sn leads to an obvious decrease from 74 to 50 kJ mol^–1 and facilitates the prompt desorption of isobutene, resulting in a high selectivity of 81.9 wt %

Promoting Effect of Sulfur Addition on the Catalytic Performance of Ni/MgAl₂O₄ Catalysts for Isobutane Dehydrogenation

Ni/MgAl₂O₄ catalysts with high NiO loadings were highly active for isobutane cracking, which led to abundant formation of methane, hydrogen and coke. The results of activity testing and XRD characterization jointly revealed that large ensembles of metallic nickel species formed during reaction notably catalyzed cracking instead of dehydrogenation. However, after introduction of sulfur into Ni/MgAl₂O₄ catalyst through impregnation with ammonium sulfate, undesired cracking reactions were effectively inhibited, and the selectivity to isobutene increased remarkably. Totally, up to ∼42 wt % isobutene could be obtained at 560 °C in a single pass after the modification. From the characterization results, it was also concluded that, after sulfur introduction, NiO particles became much smaller and better dispersed on the catalyst surface. NiS species, formed during the induction period of the reaction, not only facilitated isobutene desorption from the catalyst, but also constituted the active sites for isobutane dehydrogenation. In addition, due to the appearance of NiS species, Ni/MgAl₂O₄ catalyst after H₂S/H₂ sulfuration exhibited a high initial activity without experiencing an induction period, further confirming the crucial role that introduced sulfur played

Highly Enantio- and Diastereoselective Vinylogous Aldol Reaction by LiCl-Assisted BINOL–Titanium Species

The first highly enantio- and diastereoselective vinylogous aldol reaction between propionyl acetate-derived Brassard’s diene and aldehydes was accomplished by titanium–lithium combined Lewis acid, affording δ-hydroxy-γ-methyl-β-methoxy acrylates. This methodology was utilized in convenient and concise construction of the polypropionate moiety in cystothiazole A and melithiazole C

Roseosporol A, the first isolation of a novel sesquiterpenoid from <i>Streptomyces roseosporus</i>

<p>A novel sesquiterpenoid, roseosporol A (<b>1</b>), together with 12 known compounds (<b>2–13</b>) were isolated from the ethyl acetate extract of <i>Lsr2</i>-deletion mutant strain of <i>Streptomyces roseosporus</i>. Their structures were determined by spectroscopic methods, including NMR, HRMS, UV, IR and ECD.</p

Tissue-Specific Accumulation, Depuration, and Transformation of Triphenyl Phosphate (TPHP) in Adult Zebrafish (Danio rerio)

Understanding bioaccumulation and metabolism is critical for evaluating the fate and potential toxicity of compounds in vivo. We recently investigated, for the first time, the bioconcentration and tissue distribution of triphenyl phosphate (TPHP) and its main metabolites in selected tissues of adult zebrafish. To further confirm the metabolites, deuterated TPHP (d₁₅-TPHP) was used in the exposure experiments at an environmentally relevant level (20 μg/L) and at 1/10 LC₅₀ (100 μg/L). After 11–14 days of exposure to 100 μg/L of d₁₅-TPHP, the accumulation and excretion of d₁₅-TPHP reached equilibrium, at which point the intestine contained the highest d₁₅-TPHP (μg/g wet weight, ww) concentration (3.12 ± 0.43), followed by the gills (2.76 ± 0.12) > brain (2.58 ± 0.19) > liver (2.30 ± 0.34) ≫ muscle (0.53 ± 0.04). The major metabolite of d₁₅-TPHP, d₁₀-diphenyl phosphate (d₁₀-DPHP), was detected at significantly higher contents in the liver and intestine, at levels up to 3.0–3.5 times those of d₁₅-TPHP. The metabolic pathways of TPHP were elucidated, including hydrolysis, hydroxylation, and glucuronic acid conjugation after hydroxylation. Finally, a physiologically based toxicokinetic (PBTK) model was used to explore the key factors influencing the bioaccumulation of d₁₅-TPHP in zebrafish. These results provide important information for the understanding of the metabolism, disposition, and toxicology of TPHP in aquatic organisms

Time-scaled phylogeographic history of epidemic Japanese encephalitis virus (JEV) genotype I (GI).

Boxes with gradient shading indicate clades GIa and GIb; posterior probabilities for their ancestral nodes are shown. Tip colors represent different sampling locations, according to the map at upper left. The base layer of the modified maps are sourced from Natural Earth, and download in GeoJSON format from website (https://geojson-maps.ash.ms/).</p