Catalyst For Aerobic Oxidation Research Articles

An Improved Catalytic Performance of Fe(III)-promoted NHPI in the Oxidation of Hydrocarbons to Hydroperoxides

N-hydroxyphthalimide (NHPI) is a promising catalyst in aerobic oxidation of hydrocarbons to corresponding hydroperoxides. We have found that a trace amount of Fe(benz)3 or Fe(acac)3 (in concentration of less than 10−1 mmol/l and with the ratio of Fe(III): NHPI = 1:500) considerably accelerates the oxidation of cyclohexene and ethylbenzene, while retaining the selectivity to hydroperoxides at a level of 90%. As a consequence, the reaction temperature could be lowered down to 50–60 °C. The promoting effect of the additives was attributed to the ability of Fe(III) complexes to generate phthalimido-N-oxyl radicals (PINO) without participation in any transformations of hydrocarbon intermediates and hydroperoxides, thus ensuring selective formation and stability of the hydroperoxides.

A partially graphitic carbon catalyst for aerobic oxidation of cyclohexane

A novel partially graphitic carbon catalyst was developed and used in the aerobic oxidation of cyclohexane to KA oil (cyclohexanol A= and K=cyclohexanone) in liquid phase. Excellent catalytic performance was achieved and the conversion of cyclohexane reached 54.8% with a high selectivity of 44.4% to KA oil at 125 °C for 8 h. The characterizations and control experiment results shows that the co-existence of the graphitic structure and amorphous part is crucial to this excellent performance.

Substrate Promiscuity of ortho-Naphthoquinone Catalyst: Catalytic Aerobic Amine Oxidation Protocols to Deaminative Cross-Coupling and N-Nitrosation

ortho-Naphthoquinone-based organocatalysts have been identified as versatile aerobic oxidation catalysts. Primary amines were readily cross-coupled with primary nitroalkanes via deaminative pathway to give nitroalkene derivatives in good to excellent yields. Secondary and tertiary amines were inert to ortho-naphthoquinone catalysts; however, secondary nitroalkanes were readily converted by ortho-naphthoquinone catalysts to the corresponding nitrite species that in situ oxidized the amines to the corresponding N-nitroso compounds. Without using harsh oxidants in a stoichiometric amount, the present catalytic aerobic oxidation protocol utilizes the substrate promiscuity feature to provide a facile access to amine oxidation products under mild reaction conditions.

Catalytic Aerobic Oxidation of Alkenes by Ag@Metal Organic Framework with High Catalytic Activity and Selectivity

By coupling of Fe2O3@SiO2 particles with metal organic Framework (MOF) the magnetic MOF structure was fabricated. Precipitation and hydrothermal methods were applied for synthesis of core and MOF. Silver nanoparticles were deposited on nickel based metal organic framework surface and magnetic Fe2O3@SiO2@MOF@Ag was obtained. Because of strong coupling between silver nanoparticles and metal organic framework, the catalyst demonstrated high catalytic activity and selectivity in aerobic oxidation of alkenes under mild conditions. The nanostructure, exhibited high catalytic activity. Alkenes oxides (epoxy alkanes) were the main products with more than 89.9 % selectivity. Composite system of silver nanoparticles supported on Fe2O3@SiO2@Metal Organic Framework has potential to be an active catalysts for aerobic oxidation of alkenes under mild conditions.

Novel and efficient Cu-based catalyst constructed by lignite alkali-oxygen oxidation products for selective aerobic oxidation of alcohols to aldehydes

Developing efficient and clean utilizing route of low-ranked lignite is a highly desirable and significant topic in view of value-added utilization of coal resources. Depolymerizing lignite into water-soluble fractions is a promising route for lignite utilization, but how to use the depolymerized mixtures efficiently becomes a critical issue for promoting the application of this route. In this study, the raw lignite was depolymerized by alkali-oxygen oxidation, and the water-soluble alkali-oxygen oxidation products (AOOPs) were directly used without tedious purification to construct novel Cu-AOOPs catalysts for aerobic oxidation of alcohols into aldehydes. Both the preparation conditions of the catalysts and the reaction parameters during the catalytic reaction were systematically studied. The structures of the catalysts were characterized in detail by SEM, TEM, Power XRD, FT-IR, XPS, TG, ICP-OES and BET. The results showed that the proposed route was feasible to prepare Cu-AOOPs catalysts for alcohol oxidation using depolymerized mixtures from lignite. The obtained Cu-AOOPs catalysts were highly efficient for the selective oxidation of benzyl alcohol, and both the conversion of benzyl alcohol and the yield of benzaldehyde could reach up to 90% under mild temperature (<100 °C) and atmospheric oxygen pressure. The Cu-AOOPs catalyst could be reused for at least 6 times without significant changes in performance and structures, indicating the catalyst had excellent stability during the oxidation reaction. Besides benzyl alcohol, the Cu-AOOPs catalyst was proved to be effective for alcohols with different structures. The strategy of using AOOPs from lignite as raw materials to construct catalysts not only provides a potential way for the value-added utilization of low rank coals but also broadens the sources of raw materials for constructing metal catalysts.

Selective aerobic allylic oxidation of α-pinene catalyzed by metalloporphyrins in the absence of solvents and additives

Selective aerobic oxidation of α-pinene to high-value products is a major challenge in chemistry. Metalloporphyrins are proved to be selective catalysts for aerobic oxidation of simple hydrocarbons. Herein, we extend this method to more complex substrates using metallodeuteroporphyrins as model catalysts. It was found that the oxidation occurs mainly on the C=C and allylic C–H bonds of α-pinene influenced by the reaction temperature, reaction time, catalyst concentration, and oxygen flow rate. Allylic C–H oxidation products are obtained with a maximum selectivity value of 78.4% using the following reaction conditions: 105°C, 7 h, 5 ppm, and 60 mL/min. The influence of the metal nuclei of the metallodeuteroporphyrins on this reaction is also investigated. It was found that metallodeuteroporphyrins with Fe3+ as the metal nucleus exhibit the highest catalytic activity.

Highly Active and Selective Ru‐PNH Catalyst in Aerobic Oxidation of Benzyl Amines

AbstractSet of [Ru(η6‐cymene)(R)XCl] (R=L1SnCl, L1GeCl L2PPh2, X=Cl or SnCl3, L1=[2‐(CH2NEt2)‐4,6‐(tBu)2C6H2]−, L2=2,6‐iPr2‐C6H3‐NH−) catalysts was tested in aerobic oxidations of primary amines. The activity of studied catalysts depends on the charge of the Ru atom that has been influenced either by donating ligands R or by character of X. Typical Ru/P catalyst [Ru(η6‐cymene)(L2PPh2)Cl2] (3) with least negative charge on the Ru atom has been observed as the most effective. The design of the phosphine ligand L2 containing amino‐phosphine PNH moiety provided efficient anchoring of complex 3 to silica gel via hydrogen bonding of the PNH functional group to SiO2 to give heterogeneous catalyst 3‐silica. This complex has been also efficiently tested in aerobic oxidation as recyclable catalyst with cumulative TON up to 6930.

Copper/TEMPO Redox Redux: Analysis of PCET Oxidation of TEMPOH by Copper(II) and the Reaction of TEMPO with Copper(I).

Copper salts and organic aminoxyls, such as TEMPO (2,2,6,6-tetramethylpiperidine-N-oxyl), are versatile catalysts for aerobic alcohol oxidation. Previous reports in the literature contain conflicting proposals concerning the redox interactions that take place between copper(I) and copper(II) salts with the aminoxyl and hydroxylamine species, TEMPO and TEMPOH, respectively. Here, we reinvestigate these reactions in an effort to resolve the conflicting claims in the literature. Under anaerobic conditions, CuIIX2 salts [X = acetate (OAc), trifluoroacetate (TFA), and triflate (OTf)] are shown to promote the rapid proton-coupled oxidation of TEMPOH to TEMPO: CuIIX2 + TEMPOH → CuIX + TEMPO + HX. In the reaction with acetate, however, slow reoxidation of CuIOAc occurs. This process requires both TEMPO and HOAc and coincides with the reduction of TEMPO to 2,2,6,6-tetramethylpiperidine. Analogous reactivity is not observed with trifluoroacetate and triflate species. Overall, the facility of the proton-coupled oxidation of TEMPOH by CuII salts suggests that this process could contribute to catalyst regeneration under aerobic oxidation conditions.

G-C3N4 modified Co3O4 as efficient catalysts for aerobic oxidation of benzyl alcohol

Graphitic carbon nitride (g-C3N4) modified Co3O4 was prepared by impregnation and pyrolysis. The obtained g-C3N4/Co3O4 was thoroughly characterized by XRD, SEM, TEM, FTIR, TG and N2 adsorption. Its catalytic performance was investigated in the aerobic oxidation of benzyl alcohol in liquid phase. High activity as well as excellent selectivity to benzaldehyde can be obtained at mild condition (at atmospheric pressure and temperature of 80 °C). H2-TPR and XPS results show that the excellent activity over modified Co3O4 comes from the cooperative action of g-C3N4 and Co3O4 components. g-C3N4/Co3O4 can also be used as an efficient catalyst for the aerobic oxidation of various aromatic alcohols. However, it is not active for the aerobic oxidation of aliphatic alcohols.

Co3O4 NPs decorated Mn-Co-O solid solution as highly selective catalyst for aerobic base-free oxidation of 5-HMF to 2,5-FDCA in water

Oxidative transformations of HMF are key routes toward a wide variety of chemicals and biofuels through an environmental friendly process. Co3O4 NPs decorated Mn-Co-O solid solution, donated as Co3O4/MnXCo, was prepared by co-precipitation method and used as non-precious metal catalyst for base-free oxidation of HMF to FDCA in the presence of O2 and water. Comprehensive characterizations such as XRD, H2-TPR, O2-TPD, XPS, NH3/CO2-TPD and TEM were used to study materials properties especially the oxygen mobility and acidity-basicity. The effect of Mn/Co molar ratio in catalyst and the reaction conditions were investigated and optimized. In addition, the kinetics of the reaction was monitored to reveal the reaction route and rate-determining step. The variation of Mn/Co molar ratio was found to affect not only HMF conversion but also distribution of products. When the Mn/Co ratio was of 0.2, the Co3O4/Mn0.2Co catalyst showed the optimal catalytic performance (i.e., >99% yield of FDCA obtained under 1 bar O2 at 140 °C after 24 h) due to the highest content of both Lewis and Brønsted acid sites on the surface, leading to the strongest ability of HMF adsorption and COOH group formation, as well as the enhanced oxygen mobility. This catalyst was shown stable after a minor deactivation (≤8%) during six recycling uses and its activity can be entirely regenerated by calcination in air.

Biomass-derived phosphorus-doped carbon materials as efficient metal-free catalysts for selective aerobic oxidation of alcohols

Heteroatom-doped carbon materials (HDCMs) with abundant active functional groups and stable structural characteristics are promising catalysts for eco-friendly metal-free catalysis.

A Cu-Doped ZIF-8 metal organic framework as a heterogeneous solid catalyst for aerobic oxidation of benzylic hydrocarbons

Cu(ii) ions doped into ZIF-8 MOFs are shown to activate C–H bonds in benzylic hydrocarbons to their corresponding alcohol/ketone products.

An active, selective, and stable manganese oxide-supported atomic Pd catalyst for aerobic oxidation of 5-hydroxymethylfurfural

An MnO2-supported atomic Pd catalyst can actively, selectively and stably convert HMF into FDCA.

Metal-functionalized carbon nanotubes for biomass conversion: base-free highly efficient and recyclable catalysts for aerobic oxidation of 5-hydroxymethylfurfural

A noble and non-noble metal-confined CNT-based catalytic system was developed for the base-free selective oxidation of 5-hydroxymethylfurfural to produce 2,5-furandicarboxylic acid and 2,5-diformylfurane.

Effect of the oxygen coordination environment of Ca–Mn oxides on the catalytic performance of Pd supported catalysts for aerobic oxidation of 5-hydroxymethyl-2-furfural

Pd/CaMn2O4 provides ideal active sites for oxygen adsorption and desorption, resulting in the promoted charge transfer ability and catalytic activity.

Preparation of ternary Pd/CeO2-nitrogen doped graphene composites as recyclable catalysts for solvent-free aerobic oxidation of benzyl alcohol

The heterogeneous catalysts based on ternary Pd/CeO2-nitrogen-doped graphene (NG) were prepared and utilized for solvent-free aerobic oxidation of benzyl alcohol to benzaldehyde in the presence of green oxidant O2. Characterization results revealed that CeO2 dramatically enhanced the dispersion of Pd nanoparticles, reduced their particle size and inhibited the Pd oxidation formation. With high lattice oxygen storage capability of CeO2, excellent electrical conductivity of NG and high catalytic activity of Pd, the ternary catalyst was designed by combining the complementary superiorities of these three components. The ternary composite Pd/5CeO2-NG exhibited significantly higher catalytic activity with turnover frequency (TOF) of 30.74 s−1 for solvent-free aerobic oxidation of benzyl alcohol compared with the corresponding binary composites including 5CeO2-NG, Pd/NG and Pd/CeO2, verifying the synergistic effect among Pd, CeO2 and NG. The ternary composite was stable and could be recycled up to 6 times without remarkable loss in the activity and selectivity towards benzaldehyde. Owing to its excellent activity, high selectivity, and exceptional stability and recyclability, the Pd/CeO2-NG composite has great application potential in the fields of organic synthesis, electrochemical biosensors and fuel cells.

Ionic liquid [Bmim][AuCl4] encapsulated in ZIF-8 as precursors to synthesize N-decorated Au catalysts for selective aerobic oxidation of alcohols

• N-decorated Au catalysts were synthesized through a two-step protocol. • The catalysts were highly active in selective oxidation reactions of a variety of alcohols. • The catalysts could be reused up to five times without any loss in activity. Here we report a novel approach to synthesize Au NPs immobilized on N-doped carbon materials. In this strategy, an ionic liquid (IL) [Bmim][AuCl 4 ] was selected as the precursor for Au NPs and porous framework of ZIF-8 as the host for the IL. Raman spectroscopy, transmission electron microscopy, N 2 physical absorption and Fourier infrared spectra confirmed that the IL was successfully incorporated in the ZIF-8 pores. Followed by a thermal treatment under inert atmosphere, highly dispersed Au NPs were obtained and stabilized by nitrogen species from the carbonization of organic ligand in the metal-organic frameworks (MOFs). The [Bmim][AuCl 4 ]@ZIF-8-6.25%- T materials exhibited high catalytic activity for the selective aerobic oxidation of alcohols, affording excellent yields (up to >99%) under atmospheric air and base-free conditions. Catalytic reaction along with catalyst characterization results revealed a strong interaction between Au NPs and N species. TEM, XRD and XPS characterization results further suggested that the N species could not only prevent the Au NPs from aggregation, but also further enhance the reaction activity.

Aerobic oxidation of alcohols using ruthenium supported on DD3 kaolin

Supported ruthenium nanoparticles were prepared through the chemical reduction of aqueous Ru(III) species previously loaded (1 or 5 wt%) onto DD3 kaolin through an ion-exchanged pathway. Resulting nanoporous materials were characterized by XRF, XRD, TEM, EDX, and N2 sorption measurements, and then used as catalysts in the liquid phase aerobic oxidation of benzyl alcohol. Benzaldehyde was obtained as the main product with a 97% yield at 100% alcohol conversion at 100 °C in the presence of Ru-DD3 (5%) using 10 mL/min O2 flow and 10 mol% of tert-butyl hydroperoxide with respect to the substrate. Oxidation tests were more efficient in the case of Ru-DD3 (5%) than with other Ru-based solids such as Ru-HZSM-5 (5%). It was also shown that, in the presence of Ru-DD3 (5%), the aerobic oxidation of benylalcohol in the presence of an amine (aniline) gives rise to the imine instead of the aldehyde through a one-pot oxidation and condensation process.

N-Heterocyclic Carbene-Modified Au-Pd Alloy Nanoparticles and Their Application as Biomimetic and Heterogeneous Catalysts.

The preparation of water-soluble, N-heterocyclic-carbene-stabilized Au-Pd alloy nanoparticles by a straightforward ligand exchange process is presented. Extensive analysis revealed excellent size retention and stability over years in water. The alloy nanoparticles were applied as biomimetic catalysts for aerobic oxidation of d-glucose, for which monometallic Au and Pd nanoparticles showed no or negligible activity. The alloy nanoparticles were further applied as titania-supported heterogeneous catalysts for the mild hydrogenation of nitroarenes and the semihydrogenation of 1,2-diphenylacetylene with a solvent-dependent selectivity switch between E- and Z-stilbene.

Vanadium-embedded mesoporous carbon microspheres as effective catalysts for selective aerobic oxidation of 5-hydroxymethyl-2-furfural into 2, 5-diformylfuran

Vanadium dioxide (VO2) embedded mesoporous carbon spheres (V-CS) were synthesized by a facile hydrothermal method followed by post thermal treatments in air. The V-CS materials were used as catalysts in the aerobic oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-diformylfuran (DFF) using atmospheric oxygen as the oxidant. The effect of reaction time, temperature, catalyst loading and solvents on the reaction were investigated. Under optimized reaction conditions, a DFF yield of 99% can be achieved. The physical and chemical properties of the catalysts were studied by FESEM, BET, XRD, FTIR, Raman, XANES and element analysis. The characterization results evidenced that the micro/mesoporous structure of the carbon spheres along with the highly dispersed vanadium dioxide species is responsible for the excellent catalytic performance. The post thermal treatment was the key step to afford the superior V-CS catalysts successfully. In addition, the catalyst did not have any significant loss in activity during the recycling test, showing good reusability.