The mechanically alloyed amorphous alloys of the Tisub.45Zrsub.38Nisub.17 composition are known for their ability to form a quasicrystalline state after thermal treatment. It is also known that the ...amorphous and quasicrystal alloys belonging to the Tisub.45Zrsub.38Nisub.17 family are able to store hydrogen and yield gravimetric densities above 2 wt.%. In this contribution, we report the results of research on the Tisub.45Zrsub.38Nisub.17 system with vanadium doped instead of titanium. We found that the amorphous samples with moderate doping (x < 20) show the ability to absorb hydrogen while maintaining the amorphous state and they transform into the novel glassy-quasicrystal phase during annealing. Those materials with higher vanadium concentrations do not form entirely amorphous structures. However, they still can absorb hydrogen easily. It was also confirmed that the in situ hydrogenation of the amorphous alloys is a straightforward process without decomposition of the alloy. In this process, hydrogen does not attach to any particular constituent of the alloy, which would lead to the formation of simple hydrides or nanoclusters. Therefore, we were able to confirm the fully amorphous nature of the deuterides/hydrides of the Tisub.45−xVsub.xZrsub.38Nisub.17 with moderate V doping.
The pivotal role of CO2 hydrogenation in mitigating emissions and generating value-added fuels and chemicals underscores the significance of catalysts in achieving high efficiency in this process. ...The influence of metal-metal oxide interactions on catalyst performance has been widely acknowledged. In this study, Co-metal oxide interaction is tailored by calcining a mixed CoAl hydroxide (i.e., CoAl layered double hydroxide and Al hydroxide) at different temperatures and subsequently explored its impact on CO2 hydrogenation. The findings reveal that a moderate Co-metal oxide interaction results in a balanced Co0-Co2+ synergy. This synergy, in turn, facilitates CO2 conversion through a HCOO route at the Co0-Co2+ interface, leading to elevated turnover frequencies for CO2 conversion and the production of methane with a selectivity surpassing 98%, while methanol and ethanol are generated as minor byproducts.
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•Co-Co/Al oxide interaction is enhanced with increasing calcination temperature.•Optimized Co0-Co2+ synergy can be achieved with moderate Co-Co/Al oxide interaction.•Optimized Co0-Co2+ synergy leads to enhanced CO2 hydrogenation activity.
With the increasing energy crisis and environmental problems, there is an urgent need to seek an efficient renewable energy source, and hydrogen energy is considered one of the most promising energy ...carriers. Magnesium is considered a promising hydrogen storage material due to its high hydrogen storage density, abundant resources, and low cost. However, sluggish kinetic performance is one of the bottlenecks hindering its practical application. The kinetic process of hydrogenation/dehydrogenation can be influenced by both external and internal factors, including temperature, pressure, elementary composition, particle size, particle surface states, irregularities in particle structure, and hydrogen diffusion coefficient. The kinetic performance of the MgHsub.2/Mg system can be effectively improved by more active sites and nucleation centers for hydrogen absorption and desorption. Herein, we briefly review and discuss the experimentally observed nucleation and growth behavior of Mg/MgHsub.2 during de/hydrogenation of MgHsub.2/Mg. In particular, the nucleation and growth behavior of MgHsub.2 during the hydrogenation of Mg is discussed from the aspect of temperature and hydrogen pressure.
Consecutive, parallel reactions and equilibria affecting the selectivity in cyclohexanone oxime.
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•Nitrobenzene hydrogenation catalyzed by Pd/C in the presence of NH2OH HCl forms ...Aniline and cyclohexanone oxime.•The best solvent are ethers followed by dichloromethane and dimethylcarbonate.•NH2OH HCl hydrogenates to NH4Cl in the presence of Pd/C as a catalyst.•Aniline in the presence of NH2OH HCl gives cyclohexanone oxime and NH4Cl favors the selectivity to cyclohexanone oxime.•An imine intermediate on catalyst surface gives CON, COX and PCNA all in equilibrium.
We studied the influence of temperature, solvent, pressure, catalysts type on the selectivity of nitrobenzene hydrogenation to cyclohexanone oxime (COX) in the presence of NH2OH. The best reaction conditions are: pressure 0.8 MPa, temperature 333 K, solvent ethers, and catalyst Pd/C5%. Other hydrogenation metal catalysts did not give comparable results. The amount of Pd/C influences the yield in COX, which rises above to 90 % at the highest load. The reaction profile shows that aniline is the reaction intermediate. Indeed, aniline as a substrate gives COX, though in lower yield than that achieved employing nitrobenzene. The NH2OH parallel hydrogenation to NH4Cl, influences positively the selectivity to COX. It has been observed that COX, cyclohexanone and N-cyclohexylideneaniline are in equilibrium in the reaction solution and all likely derive from nucleophilic substitutions to a common imine intermediate formed on the Pd surface, whose high activity does not need any further metal catalyst.
N-formylation of amines utilizing CO2 in the presence of reducing agents constitute an important methodology in organic synthesis. Presented herein is a selective N-formylation of amines with CO2 and ...H2 catalyzed by complexes of Earth-abundant cobalt. A wide range of amines were converted to their corresponding formamides under CO2 and H2 pressure, catalyzed by Co-PNP pincer complex, generating water as the sole byproduct.
A stable Zr-based metal-organic framework (MOF), MOF-808, was used as a promising support to immobilize metallic Ru for the first time. The skeleton structure of MOF-808 can be well preserved during ...the immobilization process. Ru nanoparticles existed both inside and outside of the MOF cavities with good dispersion. The developed Ru/MOF-808 composite was found to be an efficient catalyst for the hydrogenation of biomass-derived levulinic acid (LA) to gamma-valerolactone (GVL). Under mild reaction conditions, full conversion of LA (100%) with high selectivity to GVL (> 99%) was achieved. The catalyst recycling and hot filtration experiments indicate that Ru/MOF-808 possesses a good catalytic stability for the LA hydrogenation reaction, although some catalyst structure changes were observed. The good immobilization effect of MOF-808 for Ru may be related to the high binding affinity between the Zr.sub.6 nodes and Ru particles. Graphic
Homogeneously catalyzed reactions often make use of additives and promotors that affect reactivity patterns and improve catalytic performance. While the role of reaction promotors is often discussed ...in view of their chemical reactivity, we demonstrate that they can be involved in catalysis indirectly. In particular, we demonstrate that promotors can adjust the thermodynamics of key transformations in homogeneous hydrogenation catalysis and enable reactions that would be unfavorable otherwise. We identified this phenomenon in a set of well-established and new Mn pincer catalysts that suffer from persistent product inhibition in ester hydrogenation. Although alkoxide base additives do not directly participate in inhibitory transformations, they can affect the equilibrium constants of these processes. Experimentally, we confirm that by varying the base promotor concentration one can control catalyst speciation and inflict substantial changes to the standard free energies of the key steps in the catalytic cycle. Despite the fact that the latter are universally assumed to be constant, we demonstrate that reaction thermodynamics and catalyst state are subject to external control. These results suggest that reaction promotors can be viewed as an integral component of the reaction medium, on its own capable of improving the catalytic performance and reshaping the seemingly rigid thermodynamic landscape of the catalytic transformation.
The rational design of metal–organic frameworks (MOFs) with hollow features and tunable porosity at the nanoscale can enhance their intrinsic properties and stimulates increasing attentions. In this ...Communication, we demonstrate that methanol can affect the coordination mode of ZIF‐67 in the presence of Co2+ and induces a mild phase transformation under solvothermal conditions. By applying this transformation process to the ZIF‐67@ZIF‐8 core–shell structures, a well‐defined hollow Zn/Co ZIF rhombic dodecahedron can be obtained. The manufacturing of hollow MOFs enables us to prepare a noble metal@MOF yolk‐shell composite with controlled spatial distribution and morphology. The enhanced gas storage and porous confinement that originate from the hollow interior and coating of ZIF‐8 confers this unique catalyst with superior activity and selectivity toward the semi‐hydrogenation of acetylene.
A mild phase transformation of ZIF‐67@ZIF‐8 core–shell structures is achieved under solvothermal conditions to generate unique hollow Zn/Co ZIF particles, which were used to generate Pd@MOF yolk‐shell composites. They exhibit enhanced gas storage and high catalytic activity and selectivity in the semi‐hydrogenation of acetylene.
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•Ruthenium N-heterocyclic carbenes are active catalysts for hydrogenation reactions.•Transfer and direct hydrogenation are covered, comprising asymmetric reductions.•Reduced ...substrates include ketones, aldehydes, olefins, nitriles, imines and esters.•Catalyst properties are easily tuned by varying wingtip and backbone substituents.•Inner and outer sphere mechanism can be evidenced, depending on the catalyst.
This review provides a brief overview of advances on ruthenium(II) N-heterocyclic carbene complexes (NHCs) applied for hydrogenation reactions undertaken during the last five years. Several structural motifs, containing mono-, bi-, tri- and tetradentate binding modes of the NHCs are discussed in combination with a variety of different wingtip substituents to provide active catalysts for hydrogenation reactions. While bidentate ligands afford the more active catalysts than their monodentate analogues, pincer ligands must be chosen carefully to enable the formation of a free coordination site in catalysis. Transfer hydrogenation and direct hydrogenation of ketones and aldehydes, olefins, nitriles, imines and esters are summarized, showing the trend towards hydrogen transfer from other sources than hydrogen gas. Recently developed chiral NHCs offer the opportunity for asymmetric transformations as a possible pathway to access natural products.
In this thesis, the diastereoselective α- and β-functionalisation of cyclic sulfoximines via lithiation-trapping and various cross-coupling reactions is described. Chapter 1 details recent ...developments in synthetic methodology used to obtain sulfoximine compounds. Chapter 2, covers the diastereoselective lithiation and trapping of four different cyclic sulfoximines with a range of electrophiles, giving the cis diastereomers. Further functionalisation of these compounds was explored using sequential lithiation-trapping reactions to give tri- and tetra-substituted sulfoximines. The diastereoselective synthesis of α- and β-aryl sulfoximines with cis stereochemistry is described in Chapter 3. Negishi cross-coupling of cyclic sulfoximines with aryl bromides was successful, giving a range of α-aryl sulfoximines. A second set of Negishi conditions was needed for the cross-coupling of heteroaromatic bromides. Different routes to vinyl sulfoximines and their cis-diastereoselective β-arylation via Hayashi-Miyaura cross-coupling are also presented in Chapter 3. Chapter 4 details the trans-diastereoselective synthesis of α- and β-aryl sulfoximines. α-Bromination of a vinyl sulfoximine and Suzuki-Miyaura cross-coupling was explored. Diastereoselective hydrogenation of the alkene gave the trans α-aryl sulfoximines. A route for the synthesis of a β-iodo vinyl sulfoximine is described. Suzuki-Miyaura cross-coupling and hydrogenation of the sulfoximine gave the trans β-aryl sulfoximines.
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