Activity For Aerobic Oxidation Research Articles

Deposition of N-doped carbon layers inside acidic ZrSBA-15: significant enhancement of catalytic performance of Pd NPs toward benzyl alcohol aerobic oxidation

Palladium-based catalysts with equably distributions of surface functionalities are synthesized by anchoring palladium nanoparticles onto N-doped carbon layers stabilized by mildly acidic platelet ZrSBA-15 framework with short mesochannels. The catalysts were fully characterized by X-ray diffraction, N2 adsorption-desorption isotherms, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy and transmission electron microscopy. Simultaneously, the Pd–NC–ZS catalysts exhibited the expectable activity in aerobic oxidation of benzyl alcohol with 82% conversion and absolute selectivity to benzaldehyde. Inappreciable loss in catalytic performance under solvent- and base-free conditions after ten times recycle demonstrated that there was strong interaction between palladium nanoparticles and the modified framework. Namely, a synergistic effect can be certified due to the surface acidic sites of ZrSBA-15 and N-doped carbon layers, which could strengthen the interaction between palladium nanoparticles and support, thus facilitating the anchoring and stabilization of palladium nanoparticles onto the pore walls of the NC–ZS.

Effect of ligand structure of Schiff base oxovanadium(IV) complexes on their catalytic activity in aerobic oxidation of alcohols

Two kinds of immobilized bidentate Schiff base oxovanadium(IV) complexes are prepared via polymer reactions and coordination reactions with chloromethylated cross-linked polystyrene (CMCPS) microspheres as matrix. Benzaldehyde (BA)-functionalized CPS microspheres, BA-CPS microspheres, were prepared through nucleophilic substitution with CMCPS microsphere as precursor and p-hydroxy benzaldehyde as reagent, and then Schiff base reactions were carried out with 3-aminopyridine (AP) and glycine (GL) as reagents, respectively, obtaining two kinds of bidentate Schiff base ligand-bonded microspheres, BAAP-CPS microspheres and BAGL-CPS microspheres. Finally, through coordination reactions with vanadyl sulfate (VOSO4) as reagent, the two kinds of immobilized bidentate Schiff base oxovanadium(IV) complex microspheres, CPS-[VO(BAAP)2] and CPS-[VO(BAGL)2], were obtained. The two immobilized complexes, VO(BAAP)2 and VO(BAGL)2, are N,N- and N,O-type bidentate Schiff base oxovanadium(IV) complexes and their ligands have different chemical structures. The two catalyst microspheres were used in oxidation of cyclohexanol and benzyl alcohol with molecular oxygen as oxidant and their catalytic activities are compared. The experimental results show that both solid catalysts can catalyze the transformation reactions of cyclohexanol and benzyl alcohol to their corresponding carbonyl compounds under mild conditions. However, CPS-[VO(BAAP)2] microspheres have much higher catalytic activity and better stability than CPS-[VO(BAGL)2] microspheres. For the immobilized bidentate Schiff base oxovanadium(IV) catalysts, the catalytic property is closely related to the chemical structures of the ligands, and for this, a theoretical explanation is given.

Dioxovanadium(V) complexes of Schiff and tetrahydro-Schiff bases encapsulated in zeolite-Y for the aerobic oxidation of styrene

A series of dioxovanadium(V) complexes of Schiff and tetrahydro-Schiff bases were encapsulated into the supercages of zeolite-Y and were characterized by X-ray diffraction, SEM, N2 adsorption/desorption, FT-IR, UV-vis spectroscopy, ICPAES, pair distribution function (PDF) and X-ray absorption near edge structure (XANES) measurements. The encapsulation is achieved by a flexible ligand method in which the transition metal cations were first ion-exchanged into zeolite-Y and then complexed with ligands. The dioxovanadium-exchanged zeolite, dioxovanadium complexes encapsulated in zeolite-Y plus non-encapsulated homogeneous counterparts were all screened as catalysts for the aerobic oxidation of styrene under mild conditions. It was found that the encapsulated complexes showed better activity than their respective nonencapsulated counterparts in most cases. All encapsulated dioxovanadium tetrahydro-Schiff base complexes showed much higher activity in aerobic oxidation of styrene than their corresponding Schiff base complexes.

Introducing Supramolecular Interactions into Robust Bis(tetrabromocatecholate) Chelated Manganese(III) Systems and Biomimetic Catalytic Activity

AbstractThis report deals with the syntheses, structures, supramolecular interactions, and biomimetic catalytic activity of three new manganese(III) complexes (1–3) containing the tetrabromocatechol ligand. Three different amines were used, with the goal of introducing their protonated species into the crystal lattice as counter cations for the robust bis(tetrabromocatecholate) chelated manganese(III) anionic species. All these systems present interesting noncovalent interactions in their crystal packing, including hydrogen bonding, halogen bonding, π –stacking and anion–π interactions. The geometrical differences (octahedral vs square pyramidal) have been analyzed by means of DFT studies, revealing that the strong anion–π interaction of pyridine with the complex anion compensates for the absence of one apical methanol molecule in 3. All of the complexes exhibited leveling catalytic activity for aerobic oxidation of 3,5‐di‐tert‐butylcatechol. DFT calculations support the formation of a stable complex‐substrate intermediate through hydrogen bonding, thereby disclosing the origin of catecholase activity of these complex anions.

Symmetrical and difunctional substituted cobalt phthalocyanines with benzoic acids fragments: Synthesis and catalytic activity

Difunctional and symmetric phthalonitriles were synthesized by nucleophilic substitution of brome and nitro-group in 4-bromo-5-nitro-phthalonitrile for residues 4-amino-, 4-hydroxyl- and 4-sulfanyl benzoic acid. Symmetrical and difunctional substituted cobalt phthalocyanines were obtained by template synthesis based on mentioned phthalonitriles. Their spectral properties and catalytic activity in aerobic oxidation of sodium [Formula: see text],[Formula: see text]-carbomoditiolate were investigated.

Pyrrolidone Modifying Gold Nanocatalysts for Enhanced Catalytic Activities in Aerobic Oxidation of Alcohols and Carbon Monoxide

Enhancing the catalytic activity of supported metal nanoparticle is a great demand but extremely challenging to make. We reported a simple strategy for enhancing the activities by employing the polyvinylpyrrolidone (PVP) additive, where a series of supported Au nanoparticle catalysts including Au/C, Au/BN, Au/TiO2, and Au/SBA-15 exhibited significantly higher activities in the oxidation of various alcohols and carbon monoxide by molecular oxygen after adding PVP to the reaction system. The XPS study indicates that PVP could electronically interact with Au to form high active Au sites for molecular oxygen, thus causing improved activities for the various oxidation reactions.

Synthesis of a Fe3O4@P4VP@metal–organic framework core–shell structure and studies of its aerobic oxidation reactivity

A novel core–shell magnetic Fe3O4@P4VP@MIL-100(Fe) composite material has been synthesized and its aerobic oxidation activity has been extensively studied.

A recoverable sandwich phosphorotungstate stabilized palladium (0) catalyst for aerobic oxidation of alcohols in water

The preparation, characterization and catalytic properties of tetra metal substituted sandwich phosphorotungstate [M4(H2O)2(PW9O34)2]10−(M4P2W18, M2+=Fe2+, Co2+, Mn2+, Cu2+, VO2+) stabilized Pd nanoparticles, which were in-situ encapsulated in mesoporous aluminum phosphate (mAPO) by a one-pot method, were demonstrated for aerobic oxidation of alcohol in water. The synthesized catalysts were characterized with N2 adsorption, XRD, TEM, FT-IR and UV–vis. TEM analysis revealed that Pd-M4P2W18/mAPO thus obtained has a mean palladium particle size of less than 5nm. The solid Pd-M4P2W18/mAPO catalysts exhibit excellent activity for aerobic oxidation of benzyl alcohols in water without any base additives. It was found the introduced M4P2W18 polyoxanions encapsulated palladium nanoparticles as both stabilizing agent and promoters, leading to enhanced activity and recyclability of palladium catalyst. The recycling test of representative Pd-(VO)4P2W18/mAPO for oxidation of benzyl alcohol suggested no significant decrease in activity and selectivity even after twelve times of successive reactions. This novel heterogeneous catalyst composed of polyoxometalates stabilized palladium nanocatalysts and mesoporous aluminophosphate can also be extended to the selective oxidation of various alcohols.

Immobilization of palladium (II) complexes on ethylenediamine functionalized core–shell magnetic nanoparticles: An efficient and recyclable catalyst for aerobic oxidation of alcohols and carbonylative Suzuki coupling reaction

A novel Pd(II) complex immobilized on ethylenediamine-functionalized core–shell magnetic nanoparticles [Fe3O4@SiO2–2N–Pd(II)] was successfully synthesized by a facile procedure, and various characterizations (TEM, XRD, FT-IR, TGA, XPS and VSM) were performed to identify its intrinsic features. The amino groups in two kinds from ethylenediamine-functionalized magnetic nanoparticles (Fe3O4@SiO2–2N) performed as robust anchors and efficient stabilizers during the fabrication of Fe3O4@SiO2–2N–Pd(II). As a heterogeneous phosphine-free Pd(II) complex catalyst, it showed excellent catalytic activity for aerobic oxidation of alcohols, and up to >99% yield of unsymmetrical biaryl ketone was obtained in the carbonylative Suzuki coupling reaction of carbon monoxide, 4-methylbenzeneboronic acid and the 4-iodonitrobenzene. Moreover, the catalyst could be completely recovered by magnetic separation from the reaction mixture and remained unaltered activity even after six repeated cycles.

Natural silk supported manganese dioxide nanostructures: Synthesis and catalytic activity in aerobic oxidation and one-pot tandem oxidative synthesis of organic compounds

Manganese dioxide nanostructures were coated on natural silk (MnO2@silk) by simple immersion of the silk fibers into a KMnO4 aqueous solution. The silk was found to act as a in situ reducing agent and substrate in aqueous KMnO4 solution for the heterogeneous production of MnO2 nanostructures. The structure of synthesized catalyst was characterized by X-ray diffraction (XRD), flame atomic absorption spectroscopy (FAAS), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) analysis. The catalytic activity of the MnO2@silk was examined in the aerobic oxidation of alkyl arenes, alcohols, and oximes to their corresponding carbonyl compounds and a one-pot tandem oxidative two-component reaction of aromatic hydrocarbons of petroleum naphtha in the absence of any other oxidizing reagent or initiator.

Pt nanoparticles interacting with graphitic nitrogen of N-doped carbon nanotubes: Effect of electronic properties on activity for aerobic oxidation of glycerol and electro-oxidation of CO

Effects of specific nitrogen functionality and oxidative functionalization of the surfaces of nitrogen-doped carbon nanotubes (NCNTs) on the interaction between Pt nanoparticles (NPs) and NCNTs have been systematically investigated. Their catalytic consequences were studied using aerobic oxidation of glycerol and electro-oxidation of CO as probing reactions. By transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and X-ray diffraction (XRD), it was revealed that nitrogen dopant obviously enhanced the dispersion of Pt NPs. Strong interaction between Pt and NCNTs was observed. Graphitic nitrogen preferentially interacted with Pt NPs, evidenced by strong electron transfer from graphitic nitrogen as electron donor to metallic Pt NPs. The oxygen-containing groups introduced by H2O2 oxidation of NCNTs may reduce the donor–acceptor interaction due to the electronegativity of oxygen. By changing the nitrogen amount of NCNTs and introducing oxygen groups, the electron enrichment of Pt NPs can be tuned. Superior catalytic activity was achieved over Pt/NCNTs in the oxidation of glycerol and electro-oxidation of CO, compared with conventional carbon nanotubes as support. Moreover, for both aerobic oxidation of glycerol and electro-oxidation of CO, it was observed that the intrinsic activity depended strongly on the electron enrichment of Pt NPs, ascribed to Pt4f7/2(0) binding energy from XPS, suggesting a promising approach to improving catalytic activity by maximizing the interaction between Pt NPs and graphitic nitrogen sites.

Efficient visible-light photocatalytic activity by band alignment in mesoporous ternary polyoxometalate-Ag2S-CdS semiconductors.

Porous multicomponent semiconductor materials show improved photocatalytic performance due to the large and accessible pore surface area and high charge separation efficiency. Here we report the synthesis of well-ordered porous polyoxometalate (POM)-Ag2S-CdS hybrid mesostructures featuring a controllable composition and high photocatalytic activity via a two-step hard-templating and topotactic ion-exchange chemical process. Ag2S compounds and polyoxometalate cluster anions with different reduction potentials, such as PW12O40(3-), SiW12O40(4-) and PMo12O40(3-), were employed as electron acceptors in these ternary heterojunction photocatalysts. Characterization by small-angle X-ray scattering, X-ray diffraction, transmission electron microscopy and N2 physisorption measurements showed hexagonal arrays of POM-Ag2S-CdS hybrid nanorods with large internal BET surface areas and uniform mesopores. The Keggin structure of the incorporated POM clusters was also verified by elemental X-ray spectroscopy microanalysis, infrared and diffuse-reflectance ultraviolet-visible spectroscopy. These new porous materials were implemented as visible-light-driven photocatalysts, displaying exceptional high activity in aerobic oxidation of various para-substituted benzyl alcohols to the corresponding carbonyl compounds. Our experiments show that the spatial separation of photogenerated electrons and holes at CdS through the potential gradient along the CdS-Ag2S-POM interfaces is responsible for the increased photocatalytic activity.

Aerobic Oxidation of Biomass-Derived 5-(Hydroxymethyl)furfural into 2,5-Diformylfuran Catalyzed by the Trimetallic Mixed Oxide (Co–Ce–Ru)

The paper deals with oxidation of the biomass-derived model molecule 5-(hydroxymethyl)furfural (HMF) catalyzed by the trimetallic mixed oxide RuCo(OH)2CeO2. The catalyst RuCo(OH)2CeO2 was prepared through alkali hydrolysis of RuCl3, Co(NO3)2, and Ce(NO3)2 and characterized by X-ray diffraction and transmission electron microscopy techniques. RuCo(OH)2CeO2 showed high catalytic activity for aerobic oxidation of HMF under mild conditions (in the case of atmospheric oxygen pressure). Various reaction parameters such as the reaction temperature, catalyst amount, solvent, and oxidant were explored. Results demonstrated that the oxidant and solvent showed a remarkable effect on the aerobic oxidation of HMF to 2,5-diformylfuran (DFF). Under optimal conditions, DFF was obtained in a high yield of 82.6% with HMF conversion of 96.5% after 12 h at 120 °C. More importantly, the catalyst could be reused several times without significant loss of its catalytic activity.

Establishing a Au Nanoparticle Size Effect in the Oxidation of Cyclohexene Using Gradually Changing Au Catalysts

The effect of the size of gold nanoparticles on their catalytic activity in aerobic oxidation of cyclohexene was established using supported gold nanoparticles that gradually undergo a change in size during the catalytic reaction. Two triphenylphosphine-stabilized clusters, Au9(PPh3)8(NO3)3 and Au101(PPh3)21Cl5, were synthesized and deposited on SiO2. The clusters did not retain their structure during the catalytic reaction; larger particles with mean diameters of ∼5–10 nm gradually formed. By combining kinetic experiments with the monitoring of catalyst transformations using transmission electron microscopy, diffuse-reflectance ultraviolet–visible spectroscopy, and X-ray photoelectron spectroscopy, we showed that catalytic activity appeared only after >2 nm Au0 particles had formed, while intact clusters and phosphine-free <2 nm particles were inactive in cyclohexene oxidation under the studied conditions.

Copper(II) Complexes with Schiff Bases Containing a Disiloxane Unit: Synthesis, Structure, Bonding Features and Catalytic Activity for Aerobic Oxidation of Benzyl Alcohol

AbstractMononuclear copper(II) salen‐type Schiff base complexes, CuIIL1–5 [H2L1 to H2L5 = tetradentate N,N,O,O ligands derived from 2‐hydroxybenzaldehyde, 2,4‐dihydroxybenzaldehyde, 3,5‐dibromo‐2‐hydroxybenzaldehyde, 2‐hydroxy‐5‐nitrobenzaldehyde, 5‐chloro‐2‐hydroxybenzaldehyde and 1,3‐bis(3‐aminopropyl)tetramethyldisiloxane, respectively] were prepared in situ in the presence of a copper(II) salt or by direct complexation between a copper(II) salt and a presynthesised Schiff base. The compounds {CuL1, CuL1·0.5Py, CuL2·0.375CH2Cl2, (CuL3)[Cu(4‐Me‐Py)4Cl]Cl·2H2O, CuL4, CuL4·CHCl3 and CuL5, as well as the isolated ligand H2L3} were characterised by elemental analysis, spectroscopic methods (IR, UV/Vis, 1H NMR, EPR) and X‐ray crystallography. The formation of a 12‐membered central chelate ring in these complexes is effected by the tetramethyldisiloxane unit, which separates the aliphatic chains, thus significantly reducing the mechanical strain in such a chelate ring. We dub this a “shoulder yoke effect” by analogy with the load‐spreading ability of such an ancient device. The coordination geometry of copper(II) in CuIIL1–5 can be described as tetrahedrally distorted square‐planar. Maximum tetrahedral distortion of the coordination geometry expressed by the parameter τ4 was observed for CuL1 (0.460), while distortion was minimal for the two crystallographically independent molecules of CuL2 (0.219 and 0.284). The Si–O–Si bond angle varies markedly between 169.75(2)° for CuL1 and 154.2(3)° for CuL4·CHCl3. Charge‐density and DFT calculations on CuL1 indicate high ionic character of the Si–O bonds in the tetramethyldisiloxane fragment. The new copper(II) complexes bearing the disiloxane moiety have been shown to act as catalyst precursors for the aerobic oxidation of benzyl alcohol to benzaldehyde mediated by the TEMPO radical, reaching yields and TONs up to 99 % and 990, respectively, under mild and environmentally friendly conditions (50 °C; MeCN/H2O, 1:1).

Preparation of Ruthenium Incorporated Heterogeneous Catalysts Using Hydroxyapatite as Catalytic Supports for Aerobic Oxidation of Alcohols

Three different kinds of hydroxyapatites (HAPs) having different sizes and compositions are prepared by hydrothermal and molten salt syntheses. Using the ion exchange reactions, ruthenium ions are incorporated on the surface of HAPs. The crystallinity, morphology and ruthenium contents are investigated by XRD, SEM, TEM and ICP. We found that smaller size of HAP having large amounts of ruthenium under ion exchange reaction shows higher catalytic activity for aerobic oxidation of alcohols.

Aerobic oxidation of primary aliphatic alcohols over bismuth oxide supported platinum catalysts in water

Catalytic oxidation of non-activated aliphatic alcohols with molecular oxygen is rather challenging, especially in an aqueous medium in the absence of an additional base. Bismuth is usually used as a promoter of platinum-based catalysts. In this work, bismuth oxide was explored as a support, and Pt0 nanoparticles supported on bismuth oxide (Pt/Bi2O3) exhibited high activity for aerobic oxidation of n-butanol using water as a solvent in the absence of an additional base under optimized conditions. Besides n-butanol, liquid primary aliphatic alcohols with low solubility in water could also be smoothly oxidized into the corresponding carbonyl compounds with molecular oxygen. Pt/Bi2O3 reduced by H2 at about 200 °C showed the highest activity for aerobic oxidation of n-butanol. At this temperature, platinum oxide was reduced to Pt0 and bismuth oxide could be reduced partially which might change the surface property of bismuth oxide.

One-Step Selective Aerobic Oxidation of Amines to Imines by Gold Nanoparticle-Loaded Rutile Titanium(IV) Oxide Plasmon Photocatalyst

Among various metal oxide-supported Au nanoparticles, Au/rutile TiO2 exhibits a particularly high level of visible-light activity for aerobic oxidation of amines to yield the corresponding imines on a synthetic scale with high selectivity (>99%) at 298 K. Experimental results have suggested that the reaction proceeds via the localized surface plasmon resonance-excited electron transfer from the Au nanoparticle to the TiO2.

Aerobic Oxidation of Amines Catalyzed by Polymer-Incarcerated Au Nanoclusters: Effect of Cluster Size and Cooperative Functional Groups in the Polymer

Abstract Aerobic oxidation reaction of amines to imines catalyzed by polymer-incarcerated Au nanoclusters (PI-Au) was developed. The effect of cluster size for this oxidation reaction was carefully examined using the same polymer support. We have succeeded in preparation of various PI-Au catalysts containing different size clusters by modification of standard preparation methods. The size of clusters and their distribution were analyzed by electron microscopy. Interestingly, catalysts containing relatively larger clusters (&amp;gt;5 nm) showed higher activity in aerobic oxidation of amines than catalysts containing smaller clusters (1–3 nm) that showed much better activity for aerobic oxidation of alcohols. In addition, novel Au nanocluster catalysts immobilized on newly prepared polymer with tertiary amine groups were developed and they showed excellent activity for aerobic oxidation of amines to imines. The relation between cluster size and catalytic activity and role of tertiary amine in polymer were discussed. These catalysts could be applied to aerobic oxidative deprotection of p-methoxybenzyl groups.

Reaction Mechanism of Aerobic Oxidation of Alcohols Conducted on Activated‐Carbon‐Supported Cobalt Oxide Catalysts

Catalytic performances and the reaction mechanism of Co(3)O(4)/AC (AC=activated carbon) for aerobic oxidation of alcohols carried out in the liquid phase were investigated. Co(3)O(4)/AC shows a high activity for aerobic oxidation of benzyl alcohol, comparable to noble metal catalysts (e.g., Au/AC) even in the absence of additives or promoters (e.g., NaOH). Changing preparation conditions, such as treatment temperature and/or time, can affect the catalytic performances of Co(3)O(4)/AC, due to decomposition of surface groups of the carbon support. Careful studies show that low alcohol conversions are obtained with either Co(3)O(4) or AC alone, which indicates that the high conversion observed over the Co(3)O(4)/AC is due to a synergistic effect between Co(3)O(4) and AC. Parallel experiments using a high-surface-area covalent triazine framework or oxygen-inert carbon nitride as support for the Co(3)O(4) catalyst also show lower conversions, which suggest that the ability of AC (in Co(3)O(4)/AC) to activate molecular oxygen is essential for the reaction. FTIR and XPS spectra taken from catalysts before and after the reaction confirm that oxygen activation proceeds mainly on the carbon support. As a result, it can be assumed that the alcohol dehydrogenation step proceeds on the metal oxide, whereas the oxygen activation step occurs mainly on the carbon support.