Atomically Dispersed Vanadium Sites Anchored on N-Doped Porous Carbon for the Efficient Oxidative Coupling of Amines to Imines

Abstract

Single-atom catalysts effectively integrate the respective advantages of homogeneous and heterogeneous catalysts and are a pioneering research frontier in catalysis by virtue of their maximized utility of metal atoms and distinct atomic configuration. However, development of such catalysts is still in the early stages. Herein, atomically dispersed vanadium (V) sites that are coordinated by N atoms and inlaid within N-incorporated porous carbon networks were prepared through a top-down strategy by annealing a V-containing metal−organic framework, NH 2 -MIL-101(V), followed by acid etching. The resulting V−N− C-600 catalyst exhibits unexpected catalytic reactivity, selectivity, and robust stability for the direct aerobic oxidation of benzylamine to generate N-benzylidene benzylamine with molecular oxygen under mild conditions. The turnover frequency reaches 53.9 h −1 , which is much superior to those achieved over the commercial V 2 O 5 and state-of-the-art non-noble metal heterogeneous catalysts reported in the literature. Kinetic analysis reveals a low activation energy barrier (37 kJ mol −1 ) for the benzylamine oxidation and indicates that a carbocationic intermediate is involved in the reaction mechanism. The synergistic effect between the isolated V single-atomic sites and N-doped hierarchically porous carbon network boosts the performance of V−N−C-600. Moreover, V−N−C-600 exhibits a wide generality for the efficient synthesis of a set of symmetrical imines, unsymmetrical imines, and imine derivatives.

Visible-light-driven photocatalytic selective oxidation of amines and sulfides over a vanadium metal–organic framework

“…The MS spectra of the corresponding products can be found in our previous study. 30 The production of H 2 O 2 was detected by a well-established DPD/POD method. 27 Typically, the filtrate obtained after the photocatalytic reaction was added to the distilled water (20 mL), extracted with EtOAc (20 mL) three times to remove the organics, and then diluted to 100 mL with distilled water.…”

Visible‐Light Photocatalytic and Photo‐bactericidal Activity of Ni‐CuWO4/OTiO2 Composite†

“…This process involves the use of unstable aldehyde, Lewis acid catalyst, dehydrating agent as well as the prolonged reaction time and the harsh reaction conditions, which restrained the practically application of those processes. [ 9‐10 ] On the other hand, the photocatalysis route has been used as the selective oxidation of primary amines to the corresponding imines, many photocatalysts, such as dye sensitized TiO 2 , [ 11 ] noble metal/TiO 2 , [ 12‐13 ] BiOX (X = Cl, Br), [ 14‐15 ] flower‐like Bi 2 WO 6 , [ 16 ] metal sulfide, [ 17‐18 ] MOFs [ 19‐20 ] and bifunctional GO [ 21 ] were involved in these processes. In addition, some photocatalysts with excellent performance have been used in photocatalytic N 2 fixation [ 22‐24 ] and water oxidation, [ 25 ] etc .…”

Quantum Dot-Embedded Hybrid Photocatalytic Nanoreactors for Visible Light Photocatalysis and Dye Degradation

“…Recently, Ogawa and co-workers fabricated mesoporous silica and titania hybrids for the photocatalytic decomposition of benzene in water . In recent times, various structurally flexible photocatalytic nanoreactors have been designed to carry out a wide range of visible light-driven chemical transformations such as CO 2 reduction, , pollutant degradation, , hydrogen (H 2 ) production, , oxidation and reduction reactions, − etc. These include metal nanocages, , carbon nanotubes, , carbon hollow structures, , yolk-shell NPs, , metal–organic frameworks (MOFs), , covalent organic frameworks (COFs), , and synthetic coordination cages. , The spatial confinement of catalysts and substrates inside the microenvironment of these nanoreactors can significantly enhance their interactions, resulting in improved catalytic efficiency via modulation of intermolecular interactions.…”