Regulating Hydrogenation Chemoselectivity of α,β-Unsaturated Aldehydes by Combination of Transfer and Catalytic Hydrogenation

Identifying Highly Active and Selective Cobalt X-Ides for Electrocatalytic Hydrogenation of Quinoline

Earth-abundant Co X-ides are emerging as promising catalysts for the electrocatalytic hydrogenation of quinoline (ECHQ), yet challenging due to the limited fundamental understanding of ECHQ mechanism on Co X-ides. This work identifies the catalytic performance differences of Co X-ides in ECHQ and provides significant insights into the catalytic mechanism of ECHQ. Among selected Co X-ides, the Co3O4 presents the best ECHQ performance with a high conversion of 98.2% and 100% selectivity at ambient conditions. The Co3O4 sites present a higher proportion of 2-coordinated hydrogen-bonded water at the interface than other Co X-ides at a low negative potential, which enhances the kinetics of subsequent water dissociation to produce H*. An ideal 1,4/2,3-H* addition pathway on Co3O4 surface with a spontaneous desorption of 1,2,3,4-tetrahydroquinoline is demonstrated through operando tracing and theoretical calculations. In comparison, the Co9S8 sites display the lowest ECHQ performance due to the high thermodynamic barrier in the H* formation step, which suppresses subsequent hydrogenation; while the ECHQ on Co(OH)F and CoP sites undergo the 1,2,3,4- and 4,3/1,2-H* addition pathway respectively with the high desorption barriers and thus low conversion of quinoline. Moreover, the Co3O4 presents a wide substrate scope and allows excellent conversion of other quinoline derivatives and N-heterocyclic substrates.

Microwave-assisted rapid synthesis and activation of ultrathin trimetal-organic framework nanosheets for efficient electrocatalytic oxygen evolution

Ultrathin metal-organic frameworks (MOFs) nanosheets have been considered as one of promising electrocatalysts for oxygen evolution reaction due to their unique structures. However, the preparation process is subject to the low-yield exfoliation and time-consuming synthetic methods. And it still requires to be explored to develop an efficient strategy for regulation of surface electronic states of MOFs to enhance their electrocatalytic activities. Herein, we report a facile microwave-assisted synthesis of NiCoFe-based trimetallic metal-organic framework (MOF) nanosheets, which can achieve simultaneously rapid synthesis and activation of MOF for OER. The as-prepared Ni₄Co₄Fe₂-MOF nanosheets exhibit excellent OER activity and electrochemical stability, which can deliver a current density of 10 mA cm^-2 at a low overpotential of 243 mV with a small Tafel slope of 48.1 mV dec^-1. This work provides a facile method for the rapid synthesis of MOF nanosheets and also demonstrates an effective approach for regulating the electronic structure of MOFs for electrocatalysis.

Ultrathin Trimetal-Organic Framework Nanosheet Electrocatalysts for the Highly Efficient Oxygen Evolution Reaction

Synthesis of ultrathin metal-organic framework (MOF) nanosheets for highly efficient oxygen evolution reaction (OER) is prevalent, but still many challenges remain. Herein, a facile and efficient three-layer method is reported for the synthesis of NiCoFe-based trimetallic MOF nanosheets, which can be directly used for the oxygen evolution reaction in alkaline conditions. The physical characterization and morphology of trimetallic MOF nanosheets were characterized by powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). By optimizing the molar ratio of Ni/Co/Fe atoms, a series of MOFs with different metal proportions were synthesized. Among them, the as-prepared (Ni₃Co₁)₃Fe₁-MOF nanosheets can deliver a current density of 10 mA cm^-2 at a low overpotential of 245 mV with a small Tafel slope of 50.9 mV dec^-1 in an alkaline electrolyte and exhibit excellent stability. More importantly, through the characterization of the intermediates in the OER process, the possible source of the catalytic active species is the electrochemically transformed metal hydroxides and oxyhydroxides.

Metal-Organic Frameworks: Synthetic Methods and Potential Applications

Metal-organic frameworks represent a porous class of materials that are build up from metal ions or oligonuclear metallic complexes and organic ligands. They can be considered as sub-class of coordination polymers and can be extended into one-dimension, two-dimensions, and three-dimensions. Depending on the size of the pores, MOFs are divided into nanoporous, mesoporous, and macroporous items. The latter two are usually amorphous. MOFs display high porosity, a large specific surface area, and high thermal stability due to the presence of coordination bonds. The pores can incorporate neutral molecules, such as solvent molecules, anions, and cations, depending on the overall charge of the MOF, gas molecules, and biomolecules. The structural diversity of the framework and the multifunctionality of the pores render this class of materials as candidates for a plethora of environmental and biomedical applications and also as catalysts, sensors, piezo/ferroelectric, thermoelectric, and magnetic materials. In the present review, the synthetic methods reported in the literature for preparing MOFs and their derived materials, and their potential applications in environment, energy, and biomedicine are discussed.

Hydrogenation of pentenal over supported Pt nanoparticles: influence of Lewis-acid sites in the conversion pathway

The superb TOF and high selectivity of Pt/CeAl are associated with the surface properties (e.g. medium Lewis acidic site). The unsaturated Ce4+/Al3+ cations pairs act as the acid sites and electron acceptors to polarize the CO bonds.

Transfer hydrogenation of alkynes into alkenes by ammonia borane over Pd-MOF catalysts

Ammonia borane with both hydridic and protic hydrogens in its structure acted as an efficient transfer hydrogenation agent for selective transformation of alkynes into alkenes in non-protic solvents.

Ultrathin two-dimensional metal-organic framework nanosheets-an emerging class of catalytic nanomaterials

The development of ultrathin two-dimensional metal-organic framework nanosheets (2D MONs) has recently attracted increasing interest due to their extensive application potential originating from their ultrathin thickness, large surface area, and innumerable accessible surface-active sites. In this frontier article, we highlight the recent developments of 2D MONs for highly efficient heterogeneous catalysts; they can be grouped into three sections in terms of their functions: (i) as catalysts capable of showing outstanding intrinsic reactivity, (ii) as support materials for prevalent catalysts, and (iii) as catalysts with multifunctional catalytic activity for diverse organic transformations. In addition, the present challenges and future opportunities in this field are also discussed.