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In this work, we will report the generation of Au clusters in a purely siliceous MCM-22 zeolite. The catalytic properties of these Au clusters have been tested for the selective oxidation of cyclohexane to cyclohexanol and cyclohexanone (KA-oil). The Au clusters encapsulated in the MCM-22 zeolite are highly active and selective for the oxidation of cyclohexane to KA-oil, which is superior to Au nanoparticles on the same support. These results suggest that Au clusters are highly active for the activation of oxygen to produce radical species. [ABSTRACT FROM AUTHOR]

The selective oxidation of cyclohexane (CHA) is still a significant challenge in the field of current catalysis chemistry and chemical industry. Here, nano-V2O5/Ti porous membrane electrodes with different morphologies, i.e., nanorods (NRs), nanosheets (NSs), and nanoparticles (NPs), were prepared by loading nano-V2O5 onto porous Ti membranes. Simultaneously, a nano-V2O5/Ti membrane electrode was employed to constitute an electrocatalytic membrane reactor (ECMR) for CHA oxidation. Results indicated that the electrochemical performance was significantly associated with the morphology of the nano-V2O5 catalysts on the membrane electrode. ECMR with V2O5 NSs/Ti electrode exhibited superior properties. Excellent electrochemical activity was obtained in the application of CHA oxidation with 28.4% conversion and 99.9% selectivity to cyclohexanone and cyclohexanol (KA oil), which is better than most noble-metal-based catalysts reported in the literature under aerobic reaction conditions. Further, a prominent catalytic activity (10.5% conversion and 99.5% selectivity to KA oil) was first achieved even under 0 °C. The preferable electrocatalytic performance of V2O5 NSs/Ti electrode for CHA oxidation was attributed to the large effective electrocatalytic surface area, high electron transfer rate, and high rate of hydroxyl radical (ṖOH) generation. Furthermore, the mechanism of CHA oxidation was explored. It was established that the valence change of V catalysts is an essential step during the selective oxidation of CHA by ECMR. Moreover, the V2O5 NSs/Ti electrode displayed excellent stability of oxidation during the selective oxidation of CHA. Therefore, our research opens up a new avenue toward the fundamental understanding and design of nanocatalysts in heterogeneous and electrochemical catalysis. [ABSTRACT FROM AUTHOR]

A porphyrinic metal–organic framework (MOF), PCN-222(Fe), was found to exhibit sound activity and selectivity to cyclohexanone and cyclohexanol (known as KA oil) toward cyclohexane oxidation. Remarkably, hydrophobicity engineering of the MOF pore walls led to significantly enhanced activity and selectivity to KA oil, far superior to that of the homogeneous porphyrin catalyst. [ABSTRACT FROM AUTHOR]

The highly selective aerobic oxidation of cyclohexane to cyclohexanone and cyclohexanol (KA-oil) under benign and green conditions is still a challenging topic. In this work, V2O5@TiO2 catalysts were prepared by V species deposited on TiO2 (P25) and characterized by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), powder X-ray diffraction (XRD), and UV-vis diffuse reflectance techniques. The selective aerobic oxidation of cyclohexane was carried out over V2O5@TiO2 catalysts with oxygen as an oxidant under simulated light irradiation. The influences of solvents, metals and mass of V species deposited on TiO2, pressure of oxygen, and reaction time on the reaction were investigated. It was found that the V species deposited on the TiO2 surface was very efficient for the photocatalytic oxidation of cyclohexane under simulated solar light irradiation. More interestingly, the selectivity of the reaction in an acetonitrile/water mixed solvent was much higher than that in other solvents. Under the optimized conditions, the selectivity to KA-oil products could be nearly 100% at a cyclohexane conversion of 18.9%. The possible pathway for the catalytic reaction was proposed. [ABSTRACT FROM AUTHOR]

Ag nanoparticles (with 2–5 nm size) supported on Mn3O4 nanorods were prepared in the presence of the cationic surfactant cetrimonium bromide using a hydrothermal method. The material was characterized in detailed by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, scanning transmission electron microscopy-mapping, Raman spectroscopy, Fourier-transformed infrared spectroscopy and inductively coupled plasma-atomic emission spectroscopy. Electron microscopy studies revealed the formation of 1D nanorods morphology. XRD revealed the formation of Mn3O4 spinel phase and TEM showed that ultrasmall-sized metallic Ag-nanoparticles deposited on Mn3O4 spinel (nanorods). This Ag/Mn3O4 nanomaterial exhibited excellent catalytic activity in the cyclohexane oxidation reaction at room temperature. The impacts of various reaction parameters (e.g. time, substrate : H2O2 molar ratio etc.) were investigated in detail. A detailed characterization study demonstrated the correlation between the physicochemical properties of the Ag–Mn oxide nanorods and their catalytic performance. A cyclohexane conversion of 88% with 75% cyclohexanone selectivity with an overall C6 selectivity (cyclohexanol + cyclohexanone) of 100% was accomplished at room temperature. The Ag/Mn3O4 catalyst hardly exhibited leaching up to eight reuses, proving its true heterogeneous nature. [ABSTRACT FROM AUTHOR]

A series of potentially tetradentate and pentadentate ligands modelled on BPMEN has been prepared and their iron(II) bis(triflate) complexes have been isolated and characterised by spectroscopic and crystallographic techniques (BPMEN = N,N'-bis(pyridylmethyl)ethylenediamine). Changes to the BPMEN ligand have invariably led to complexes with different coordination modes or geometries and with inferior catalytic efficiencies for the oxidation of cyclohexane with H2O2. The reaction of an iron(II) complex containing a pentadentate BPMEN-type ligand with O2 has resulted in ligand degradation via oxidative N-dealkylation and the isolation of a bis(hydroxo)-bridged dinuclear iron(III) complex with a picolinatetype ligand. [ABSTRACT FROM AUTHOR]

Two multinuclear complexes [Fe6(μ3-O)2(μ4-O2)L10(OAc)2(H2O)2]·2.625Et2O·2.375H2O (1) and [FeIII11Cl(μ4-O)3(μ3-O)5L16(dmf)2.5(H2O)0.5]·Et2O·1.25dmf·3.8H2O (2), where HL = 3,4,5-trimethoxybenzoic acid and dmf = dimethylformamide, have been prepared from trinuclear iron(iii) carboxylates via their structural rearrangement in dimethylformamide or diethyl ether–dimethylformamide 9 : 1, respectively, and slow vapor diffusion of diethyl ether into the reaction mixture. Both compounds have been characterized by X-ray diffraction, optical, Mössbauer spectroscopy, and magnetic measurements. Complex 1 possesses a hexanuclear ferric peroxido–dioxido {Fe6(O2)(O)2}12+ core unit, which adopts a recliner conformation, while complex 2 contains an unprecedented {Fe11O8Cl}16+ core, in which 9 ferric ions are six-coordinate and the remaining two are five-coordinate. Another structural feature of note of the undecanuclear core is the presence of a deformed cubane entity {Fe4(μ3-O)(μ4-O)3}4+. Both complexes act as catalyst precursors for the oxidation of cyclohexane to cyclohexanol and cyclohexanone with aqueous H2O2, in the presence of pyrazinecarboxylic acid. Remarkable TONs and TOFs (the latter mainly for 1) with concomitant quite good yields have been achieved under mild conditions. Moreover, 1 exhibits remarkably high activity in an exceptionally short reaction time (45 min), being unprecedented for any metal catalyzed alkane oxidation by H2O2. The catalytic reactions proceed via Fenton type chemistry. [ABSTRACT FROM AUTHOR]

A new binuclear oxovanadium(v) complex [{VO(OEt)(EtOH)}2L] (1) where H4L is bis(2-hydroxybenzylidene)terephthalohydrazide has been synthesized and fully characterized. The combination of 1 with pyrazine-2-carboxylic acid (PCA; a cocatalyst) affords a catalytic system for the efficient oxidation of saturated hydrocarbons, RH, with hydrogen peroxide and air in acetonitrile solution at 50 °C to produce alkyl hydroperoxides, ROOH, as the main primary products. Very high turnover numbers (TONs) have been attained in this reaction: for example, after 2220 min, TON = 44 000 and initial TOF (turnover frequency) = 3300 h−1 per molecule of complex 1. The estimated activation energy of the cyclohexane oxygenation in the presence of 1/PCA is Ea = 16 ± 2 kcal mol−1. This value is identical to that obtained for the cyclohexane oxidation with H2O2 catalyzed by the (n-Bu4N)[VO3]/PCA combination (17 ± 2 kcal mol−1). The dependences of initial oxidation rates W0 on the initial concentrations of all components of the reaction mixture have been determined. Based on these kinetic data and on the regio- and bond-selectivity parameters measured in the oxidation of linear and branched alkanes a mechanism of the oxidation has been proposed which includes the generation of hydroxyl radicals in the crucial stage. [ABSTRACT FROM AUTHOR]

A new binuclear oxovanadium(v) complex [{VO(OEt)(EtOH)}2L] (1) where H4L is bis(2-hydroxybenzylidene)terephthalohydrazide has been synthesized and fully characterized. The combination of 1 with pyrazine-2-carboxylic acid (PCA; a cocatalyst) affords a catalytic system for the efficient oxidation of saturated hydrocarbons, RH, with hydrogen peroxide and air in acetonitrile solution at 50 °C to produce alkyl hydroperoxides, ROOH, as the main primary products. Very high turnover numbers (TONs) have been attained in this reaction: for example, after 2220 min, TON = 44 000 and initial TOF (turnover frequency) = 3300 h−1 per molecule of complex 1. The estimated activation energy of the cyclohexane oxygenation in the presence of 1/PCA is Ea = 16 ± 2 kcal mol−1. This value is identical to that obtained for the cyclohexane oxidation with H2O2 catalyzed by the (n-Bu4N)[VO3]/PCA combination (17 ± 2 kcal mol−1). The dependences of initial oxidation rates W0 on the initial concentrations of all components of the reaction mixture have been determined. Based on these kinetic data and on the regio- and bond-selectivity parameters measured in the oxidation of linear and branched alkanes a mechanism of the oxidation has been proposed which includes the generation of hydroxyl radicals in the crucial stage. [ABSTRACT FROM AUTHOR]

Photocatalytic oxidation of cyclohexane (CHA) with molecular oxygen has been performed with hydrophobic Cr–Si mixed oxides as a catalyst under visible light irradiation (λ ＞ 400 nm). The Cr–Si catalysts with highly dispersed chromate species were prepared by hydrolysis of tetraethyl orthosilicate (TEOS), organoalkoxysilane (1,2-bis(triethoxysilyl)ethane: BTESE), and Cr(NO3)3 followed by calcination. All of the Cr–Si catalysts promote partial oxidation of CHA to cyclohexanol (CHA-ol) and cyclohexanone (CHA-one) with high selectivity (＞99%). Among the Cr–Si catalysts prepared with different TEOS and BTESE compositions, the catalyst prepared with 10% BTESE demonstrates the highest catalytic activity. The CHA vapor adsorption and electron spin resonance analysis reveal that the enhanced catalytic activity is due to the increased hydrophobicity of the catalyst surface, which enhances the access of CHA to the excited state chromate species. [ABSTRACT FROM AUTHOR]

The new mononuclear [Cu(Hbdea)2]·2Hdnba (1), dinuclear [Cu2(μ-Hbdea)2(N3)2] (2) and [Cu2(μ-Hbdea)2(pta)2]·2H2O (3), and 1D polymeric [Cu2(μ-Hbdea)2(μ-tpa)]n.2nH2O (4) copper(II) compounds have been prepared by self-assembly, in aqueous alkali medium and at ambient conditions, from Cu(II) acetate, N-butyldiethanolamine (H2bdea) and the corresponding auxiliary reagents, 3,5-dinitrobenzoic acid (Hdnba), sodium azide, p-toluic acid (Hpta) and terephthalic acid (H2tpa), respectively. They have been fully characterized by IR spectroscopy, FAB-MS+, elemental and single-crystal X-ray diffraction analyses, the latter also revealing intensive intermolecular hydrogen bonding in 2-4, resulting in the extension of the structural motifs and generation of tetrameric aggregates (in 2) and 1D(in 3) or 2D (in 4) supramolecular networks. All compounds constitute the first examples of Cu complexes derived from N-butyldiethanolamine, while 4 represents also the first coordination polymer bearing this ligand. Magnetic susceptibility measurements reveal that compound 1 follows the Curie-Weiss law, whereas 2-4 follow the Bleaney-Bowers dinuclear model displaying antiferromagnetic coupling. Compounds 1-4 act as valuable catalyst precursors for the mild peroxidative oxidation of cyclohexane, by aqueous H2O2 in acidic MeCN medium, to cyclohexanol and cyclohexanone with overall yields up to 38%. The effects of various acid additives (promoters) have been studied, showing the preferable use of trifluoroacetic (TFA), nitric and hydrochloric acids. [ABSTRACT FROM AUTHOR]