Full Selectivity Control over the Catalytic Hydrogenation of Nitroaromatics Into Six Products.

A full selectivity control over the catalytic hydrogenation of nitroaromatics leads to the production of six possible products, i.e., nitroso, hydroxylamine, azoxy, azo, hydrazo or aniline compounds, which has however not been achieved in the field of heterogeneous catalysis. Currently, there is no sufficient evidence to support that the catalytic hydrogenation of nitroaromatics with the use of heterogeneous metal catalysts would follow the Haber's mechanistic scheme based on electrochemical reduction. We now demonstrate in this work that it is possible to fully control the catalytic hydrogenation of nitroaromatics into their all six products using a single catalytic system under various conditions. Employing SnO2-supported Pt nanoparticles facilitated by the surface coordination of ethylenediamine and vanadium species enabled this unprecedented selectivity control. Through systematic investigation into the controlled production of all products and their chemical reactivities, we have constructed a detailed reaction network for the catalytic hydrogenation of nitroaromatics. Crucially, using oxygen-isolated characterization techniques is essential for identifying unstable compounds such as nitroso, hydroxylamine, hydrazo compounds. The insights gained from this research offer invaluable guidance for selectively transforming nitroaromatics into a wide array of functional N-containing compounds, both advancing fundamental understanding and fostering practical applications in various fields.

Heterogeneous Hydrogenation with Hydrogen Spillover Enabled by Nitrogen Vacancies on Boron Nitride-Supported Pd Nanoparticles.

Heterogeneous hydrogenation with hydrogen spillover has been demonstrated as an effective route to achieve high selectivity towards target products. More effort should be paid to understand the complicated correlation between the nature of supports and hydrogenation involving hydrogen spillover. Herein, we report the development of the hydrogenation system of hexagonal boron nitride (h-BN)-supported Pd nanoparticles for the hydrogenation of aldehydes/ketones to alcohols with hydrogen spillover. Nitrogen vacancies in h-BN determine the feasibility of hydrogen spillover from Pd to h-BN. The hydrogenation of aldehydes/ketones with hydrogen spillover from Pd proceeds on nitrogen vacancies on h-BN. The weak adsorption of alcohols to h-BN inhibits the deep hydrogenation of aldehydes/ketones, thus leading to high catalytic selectivity to alcohols. Moreover, the hydrogen spillover-based hydrogenation mechanism makes the catalyst system exhibit a high tolerance to CO poisoning.

Hierarchically Ordered Porous Carbon with Atomically Dispersed FeN4 for Ultraefficient Oxygen Reduction Reaction in Proton-Exchange Membrane Fuel Cells.

The low catalytic activity and poor mass transport capacity of platinum group metal free (PGM-free) catalysts seriously restrict the application of proton-exchange membrane fuel cells (PEMFCs). Catalysts derived from Fe-doped ZIF-8 could in theory be as active as Pt/C thanks to the high intrinsic activity of FeN4 ; however, the micropores fail to meet rapid mass transfer. Herein, an ordered hierarchical porous structure is introduced into Fe-doped ZIF-8 single crystals, which were subsequently carbonized to obtain an FeN4 -doped hierarchical ordered porous carbon (FeN4 /HOPC) skeleton. The optimal catalyst FeN4 /HOPC-c-1000 shows excellent performance with a half-wave potential of 0.80 V in 0.5 m H2 SO4 solution, only 20 mV lower than that of commercial Pt/C (0.82 V). In a real PEMFC, FeN4 /HOPC-c-1000 exhibits significantly enhanced current density and power density relative to FeN4 /C, which does not have an optimized pore structure, implying an efficient utilization of the active sites and enhanced mass transfer to promote the oxygen reduction reaction (ORR).

The DUF288 domain containing proteins GhSTLs participate in cotton fiber cellulose synthesis and impact on fiber elongation.

Cotton is one of the most important economic crops in the world, with over 90 % cellulose in the mature fiber. However, the cellulose synthesis mechanism in cotton fibers is poorly understood. Here, we identified four DUF288 domain containing proteins, which we designated GhSTL1-4. These four GhSTL genes are highly expressed in 6 days post anthesis (dpa) and 20 dpa cotton fibers. They are localized to the Golgi apparatus, and can rescue the growth defects in primary cell wall (PCW) and secondary cell wall (SCW) of cellulose synthesis of the Arabidopsis stl1stl2 double mutant at varying degrees. Silencing of GhSTLs resulted in reduced cellulose content and shorter fibers. In addition, split-ubiquitin membrane yeast two-hybrid analysis showed that GhSTL1 and GhSTL4 can interact with PCW-related GhCesA6-1/6-3 and SCW-associated GhCesA7-1/7-2. GhSTL3 can interact with SCW-related GhCesA4-3. These interactions are further confirmed by firefly luciferase complementation imaging assay. Together, we demonstrate that GhSTLs can selectively interact with both the PCW and SCW-associated GhCesAs and impact on cellulose synthesis and fiber development. Our findings provide insights into the mechanism underlying cellulose biosynthesis in cotton fibers, and offer potential candidate genes to coordinate PCW and SCW cellulose synthesis of cotton fibers for developing elite cotton varieties with enhanced fiber quality.

Rational Design of Hierarchical, Porous, Co-Supported, N-Doped Carbon Architectures as Electrocatalyst for Oxygen Reduction.

Developing highly active nonprecious-metal catalysts for the oxygen reduction reaction (ORR) is of great significance for reducing the cost of fuel cells. 3D-ordered porous structures could substantially improve the performance of the catalysts because of their excellent mass-diffusion properties and high specific surface areas. Herein, ordered porous ZIF-67 was prepared by forced molding of a polystyrene template, and Co-supported, N-doped, 3D-ordered porous carbon (Co-NOPC) was obtained after further carbonization. Co-NOPC exhibited excellent performance for the ORR in an alkaline medium with a half-wave potential of 0.86 V vs. reversible hydrogen electrode (RHE), which is higher than that of the state-of-the-art Pt/C (0.85 V vs. RHE). Moreover, the substantially improved catalytic performance of Co-NOPC compared with Co-supported, N-doped carbon revealed the key role of its hierarchical porosity in boosting the ORR. Co-NOPC also exhibited a close-to-ideal four-electron transfer path, long-term durability, and resistance to methanol penetration, which make it promising for large-scale application.

Soft-templated mesoporous carbon-modified glassy carbon electrode for sensitive and selective detection of aristolochic acids.

In this study, ordered mesoporous carbon (OMC) was synthesized by applying a soft template method, and its mesoporous structure was characterized by scanning electron microscopy, transmission electron microscopy, and nitrogen adsorption-desorption techniques. X-ray diffraction and Raman spectroscopic analyses were conducted to demonstrate the high graphitization and topological defects at the sample surface. An electrochemical sensor based on an OMC-modified glassy carbon electrode (OMC/GCE) was constructed to detect aristolochic acids (AAs) using cyclic voltammetry and linear sweep voltammetry. The dependence of the experimental parameters including solution pH, scan rate, and accumulation time were examined and optimized. Under the optimal conditions, the response of OMC/GCE was linear over wide concentration ranges of AAs (0.6-10 µM and 10-50 µM), with sensitivities of -1.77 and -0.31 µA/µM, respectively. The limit of detection was calculated to be 0.186 µM (at S/N = 3). Furthermore, the proposed OMC/GCE was applied to detect AAs in Asarum sieboldini and the content of AAs was calculated to be 8.9 µg/g with high accuracy and precision. In addition, the modified electrode also exhibited good selectivity, reproducibility, and stability. Therefore, the OMC/GCE can be used as a platform for the determination of AAs.

Differential pulse voltammetry detection of Pb(ii) using nitrogen-doped activated nanoporous carbon from almond shells.

Almond shell-based charcoal was prepared by carbonizing almond shells in a nitrogen atmosphere. Nanoporous carbon (NPC) was formed via activating the obtained charcoal using potassium hydroxide as an activating agent, followed by the synthesis of nitrogen-doped nanoporous carbon (N-NPC) via a hydrothermal reaction using urea as the nitrogen source. The obtained N-NPC possessed a large surface area (1075 m2 g-1), narrow pore-size distribution (1-2 nm) and nitrogen content reaching 2.23 wt%. Using N-NPC with Nafion to modify a glassy carbon electrode, a highly sensitive electrochemical sensor was fabricated for the determination of Pb(ii) in aqueous solutions with differential pulse anodic stripping voltammetry (DPASV). The peak current of Pb(ii) showed linearity over concentrations from 2.0 to 120 µg L-1 and the detection limit (S/N = 3) was estimated to be 0.7 µg L-1 for Pb(ii), which was 15-fold lower than the guideline value of drinking water given by the World Health Organization (WHO). The experimental data indicated that this easy and low-cost method is an accurate and fast method for the detection of trace Pb(ii).