Catalyst For Selective Aerobic Oxidation Research Articles

Ru nanoclusters supported on a bimodal N,S-doped mesoporous carbon: an efficient and reusable catalyst for selective aerobic oxidation of alcohols and amines

Ru nanoparticles supported on a bimodal N, S-doped mesoporous carbon catalyzing the oxidation of various alcohols and amines, giving the respective aldehydes/ketones and nitriles/imines in high yields and selectivity.

Catalytic Activity of Nonaggregating Cu Nanoparticles Supported in Pores of Zeolite for Aerobic Oxidation of Benzyl Alcohol.

Cu nanoparticles (NPs) as catalysts have the good advantage of being more abundant than noble metal NPs. In this study, we synthesized nonaggregating Cu NPs supported in Y-type zeolite by the photoreduction method. In this method, Cu ions in pores of zeolite can be slowly reduced with a small amount of reductant at room temperature. The high-resolution transmission electron microscope, energy dispersive X-ray spectroscopy, X-ray diffraction patterns, and UV-Vis spectra supported that nonaggregating Cu NPs existed in the pores of zeolite. Catalytic activities of Cu NP-zeolite were investigated for the aerobic oxidation of benzyl alcohol. Our Cu NP-zeolite had a large turnover frequency of 17 h-1. The yield of benzaldehyde increased in proportion to the amount of Cu loading at ≤0.5 wt %, indicating that Cu NPs in pores of zeolite work as catalysts for selective aerobic oxidation of benzyl alcohol. The high catalytic activity was brought by nonaggregating Cu NPs in pores of zeolite. The catalytic reaction for other aromatic alcohols with electron-donating groups proceeded, whereas it did not proceed for the aromatic alcohols with electron-withdrawing groups or aliphatic alcohols, indicating that the interaction between zeolite and the benzene ring also contributed to the reaction. This study would be expected to contribute to the development of Cu NP catalysts.

Organic-inorganic hybridized Mo/Pd-based complexes as efficient catalysts for selective aerobic oxidation of benzyl alcohols

Organic-inorganic hybrid crystalline compounds have demonstrated outstanding potential utilization in a wide range of catalytic applications. Herein, three organic–inorganic hybrids Mo/Pd-based complexes Mo2O4(CF3COO)2(DMSO)4 (compound 1), Pd(C6H5CH2)2NCS2)2 (compound 2) and Pd[(CH3)2CHCH2NCS2]2 (compound 3) have been controllably synthesized and fully characterized. Remarkably, benefiting from coordinated solvent molecules, the dinuclear oxomolybdates 1 exhibits the efficient homogeneous catalytic activities for the selective aerobic oxidation of benzyl alcohols under ambient pressure (yields up to 90%). Moreover, compound 1 can be reused three cycles in the reactions without significant loss of activity and the possible catalytic mechanisms also be proposed.

Mechanism-Guided Design of Robust Palladium Catalysts for Selective Aerobic Oxidation of Polyols

The palladium complex [(L1)Pd(μ-OAc)]2[OTf]2 (L1 = neocuproine) is a selective catalyst for the aerobic oxidation of vicinal polyols to α-hydroxyketones, but competitive oxidation of the ligand methyl groups limits the turnover number and necessitates high Pd loadings. Replacement of the neocuproine ligand with 2,2'-biquinoline ligands was investigated as a strategy to improve catalyst performance and explore the relationship between ligand structure and reactivity. Evaluation of [(L2)Pd(μ-OAc)]2[OTf]2 (L2 = 2,2'-biquinoline) as a catalyst for aerobic alcohol oxidation revealed a threefold enhancement in turnover number relative to the neocuproine congener, but a much slower rate. Mechanistic studies indicated that the slow rates observed with L2 were a consequence of precipitation of an insoluble trinuclear palladium species─(L2Pd)3(μ-O)22+─formed during catalysis and characterized by high-resolution electrospray ionization mass spectrometry. Density functional theory was used to predict that a sterically modified biquinoline ligand, L3 = 7,7'-di-tert-butyl-2,2'-biquinoline, would disfavor the formation of the trinuclear (LPd)3(μ-O)22+ species. This design strategy was validated as catalytic aerobic oxidation with [(L3)Pd(μ-OAc)]2[OTf]2 is both robust and rapid, marrying the kinetics of the parent L1-supported system with the high aerobic turnover numbers of the L2-supported system. Changes in ligand structure were also found to modulate regioselectivity in the oxidation of complex glycoside substrates, providing new insights into structure-selectivity relationships with this class of catalysts.

Atomically Defined Undercoordinated Copper Active Sites over Nitrogen-Doped Carbon for Aerobic Oxidation of Alcohols.

Selective aerobic oxidation of alcohols offers an attractive means to address challenges in the modern chemical industry, but the development of non-noble metal catalysts with superior efficacy for this reaction remains a grand challenge. Here, this study reports on such a catalyst based on atomically defined undercoordinated copper atoms over nitrogen-doped carbon support as an efficient, durable, and scalable heterogeneous catalyst for selective aerobic oxidation of alcohols. This catalyst exhibits extremely high intrinsic catalytic activity (TOF of 7692 h-1 ) in the oxidation of cinnamyl alcohol to afford cinnamaldehyde, along with exceptional recyclability (at least eight cycles), scalability, and broad substrate scope. DFT calculations suggest that the high activity derives from the low oxidation state and the unique coordination environment of the copper sites in the catalyst. These findings pave the way for the design of highly active and stable single atom catalysts to potentially address challenges in synthetic chemistry.

Co-immobilization of N-hydroxyphthalimide and cobaltous ions as a recyclable catalyst for selective aerobic oxidation of toluene to benzaldehyde

Selective aerobic oxidation of toluene to benzaldehyde has gained vast attentions due to its characteristics in environmental friendliness, atomic economy and a waiver of chlorine contamination. The separation, recovery and reuse of homogeneous catalysts will, however, be tricky. In this work, cobalt ions were immobilized by coprecipitation followed by a special washing, and the prepared cobalt-containing intermediate exhibited excellent textural properties and an exclusively low chemical state. 3-(Glycidoxypropyl) trimethoxysilicane (GPTMS) was used as a linking molecule to anchor N-hydroxyphthalimide (NHPI) onto the intermediate by C–O–N and Si–O–Si bonds, respectively, and a reliable covalent combination of NHPI was confirmed by the decomposition temperature and chemical states of N element in the co-immobilized NHPI/Co catalyst. The synthesized NHPI-GPTMS-CS catalyst exhibited a toluene conversion of 42.5% and a selectivity to benzaldehyde of 52.6% in hexafluoropropan-2-ol, which is much higher than the reactivity of toluene observed on the catalyst combination of commercial silica anchored NHPI (NHPI-GPTMS-SiO2) and homogeneous cobaltous ions, testifying an accessibility and a better synergy between N-oxyl radicals and cobaltous ions co-immobilized. There was no appreciable leaching of cobalt species and anchored NHPI observed for the co-immobilized catalyst and its activity for toluene oxidation was well remained, indicating an excellent reusable capability. It was observed that benzaldehyde is converted into benzoic acid, but benzyl alcohol into benzaldehyde and toluene via oxidation and disproportionation, respectively, over the synthesized co-immobilized catalyst. Toluene oxidation is suggested to proceed via a free radical mode and the produced water is one of the quenching agents.

A green, reusable and remarkable catalyst for selective aerobic oxidation of alcohols: Construction of Cu(BDC) on the surface of carboxymethyl cellulose fiber

Removing or reducing the amount of metal used in catalytic methods is one of the most important concerns of today's activists in the field of green chemistry. In the present paper, copper terephthalate metal-organic framework (MOF) is chemically attached to carboxymethyl cellulose fiber via an in-situ synthesizing method. The synthesized novel hybrid material (Cu(BDC)/CMC) was applied as an efficient, reusable, and environmentally benign heterogeneous catalyst for the aerobic oxidation of alcohols to the corresponding aldehydes and ketones with good yields under mild conditions. FT-IR, XRD, TGA, SEM, EDS, and TEM techniques confirmed successful construction of catalyst. Obtained results revealed that primary aromatic alcohols are easily converted to aromatic aldehydes in high yields (from 70 to 94 %) with the zero-order kinetics model without additional oxidation to carboxylic acids compared to secondary aromatic alcohols (yields: from 6 to 22). The outstanding advantages of the synthesized catalyst are a non‐hazardous catalyst, desired yields, good selectivity, operational simplicity, mild reaction conditions, and reusability. On the other hand, this catalytic system overcomes essential defects of copper terephthalate MOFs as a catalyst, such as poisoning, deactivation, and non-reusability nature.

Rational construction of metal–base synergetic sites on Au/Mg-beta catalyst for selective aerobic oxidation of 5-hydroxymethylfurfural

The selective aerobic oxidation of biomass-derived 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid (FDCA, a potential renewable substitution of fossil-based terephthalic acid to produce polyethylene 2,5-furandicarboxylate plastic) is an appealing transformation for constructing eco-friendly and sustainable chemical processes. Au supported catalysts have showed encouraging performances for this well-received conversion, whose catalytic behavior was greatly affected by the adopted support derived from the existence of metal-support interactions. Herein, a series of Mg-Beta zeolites were hydrothermally synthesized via developed structural reconstruction, which were employed as basic supports for Au catalysts to construct bifunctional catalysts. The relationship between structure (Au particle size, basicity within zeolites and Auδ+ contents) and FDCA yield was concretely established. The conclusion was made that the utilization of Mg-Beta zeolites with strong basicity as the support could not only improve the FDCA yield but also decrease the amount of additional base. Furthermore, the possible reaction mechanism was also proposed via tracking time-dependent variations of corresponding organics and controlled experiment. This work provides some guidance for rationally designing multifunctional catalysts in the view of integrating metal catalysts with metallosilicate zeolites, which was beneficial to the catalytic upgrading of organic compounds with multiple functional groups.

Hierarchically Porous Hydrothermal Carbon Microspheres Supported N-Hydroxyphthalimide as a Green and Recyclable Catalyst for Selective Aerobic Oxidation of Alcohols.

A novel metal-free, reusable, and green catalytic system comprising hydrothermal carbon microspheres (HCMSs) supporting N-hydroxyphthalimide (NHPI) was developed and employed in the aerobic oxidation of alcohol. Hierarchically porous HCMSs with good monodispersity were produced by the hydrothermal carbonization of sucrose and designed NaOH-impregnated calcination under a static air atmosphere. The meso- and macroporous pores on HCMSs make up 71% of the total pore volume. The covalent immobilization of NHPI onto HCMSs was first accomplished by grafting hyperbranched polyquaternary amine via repetitive ring-opening reactions of diglycidyl ether and subsequent amidation with 4-carboxy-NHPI. Owing to the cocatalysis of grafted quaternary ammonium salt, a designed heterogeneous catalyst has superior performance to free NHPI in the oxidation of 2-phenylethanol. The established catalytic system achieved 42% conversion and up to 96% selectivity of acetophenone at 90 °C under 1 atm O2 for 20 h and presented a versatile catalytic effect for diversified alcohols. Immobilized NHPI could be facilely recycled via simple filtration and displayed good stability for six cycles without a discernible decrease of reactivity or damage of catalyst morphology in repeated oxidation test.

Uranyl-MOF for Thioether Oxidation Processes Under Visible Light Conditions

In this study, we describe the synthetic of uranyl nitrate ion functionalized MOFs linked by carboxyl, which displays block shape crystals structure. The as-prepared uranyl-MOF has been efficiently utilized as heterogeneous catalyst for selective aerobic oxidation of sulfides under visible-light irradiation. Photochemistry of extended MOFs including uranyl nitrate ion has been examined. The sulfoxidation reaction proceeds with good yields for a large variety of different sulfides. This process is carried out under visible light conditions, methanol as single solvent, and the uranyl-MOF material can be recycled up to five times. Sulfoxidation reaction mainly proceeds through an electron and energy transfer mechanism of oxygen in uranyl nitrate ion. In this study, we describe the synthetic of uranyl nitrate ion functionalized MOFs. The as-prepared uranyl-MOF was efficiently utilized as heterogeneous catalyst for selective aerobic oxidation of sulfides under visible-light irradiation. Photochemistry of extended MOFs including uranyl nitrate ion has been examined.

Hydroxyapatite‐supported Manganese Oxides as Efficient Non‐noble‐metal Catalysts for Selective Aerobic Oxidation of Alcohols

AbstractIn this article, hydroxyapatites (HAPs) with different Ca/P ratios have been synthesized as the supports to prepare the MnOx/HAP catalysts for the aerobic oxidation of alcohols. The catalytic activity is strongly influenced by the Ca/P ratio and the calcination temperature as they can affect the acid and basic properties and oxidation state of MnOx of the catalysts. The optimized catalyst MnOx/HAP‐10 can catalyze various primary alcohols to the corresponding aldehydes selectively with excellent conversion (up to 100 %), and can be easily recovered and reused at least four times without any appreciable loss of activity.

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.

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.

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.

Vitamin B12 supported on graphene oxide: As a bio‐based catalyst for selective aerobic oxidation of alcohols

The environmental impact of chemical processes has now opened new windows of opportunity for bio‐based catalysts. In this paper a highly active bio‐based catalyst of vitamin B12 supported on graphene oxide nanosheets is reported for the selective aerobic oxidation of alcohols to the corresponding carbonyl compounds. Operational simplicity, mild reaction conditions, high yield and selectivity, non‐hazardous nature, commercial availability and affordability are the main advantages of this novel catalytic system.

P(AA)-Pd nanoreactor as a green catalyst for selective aerobic oxidation of primary alcohols and reduction of nitrophenol

p(AA)-Pd nanoreactor as a green catalyst for selective aerobic oxidation of primary alcohols and reduction of nitrophenol

TEMPO-Appended Metal-Organic Frameworks as Highly Active, Selective, and Reusable Catalysts for Mild Aerobic Oxidation of Alcohols.

Metal-organic frameworks (MOFs) decorated with stable organic radicals are highly promising materials for redox catalysis. Unfortunately however, the synthesis of chemically robust MOFs typically requires harsh solvothermal conditions, which are not compatible with organic radicals. Here, we describe the synthesis of two isoreticular families of stable, mixed component, zirconium MOFs with UiO-66 and UiO-67 structures and controlled amounts of covalently attached TEMPO radicals. The materials were obtained using a relatively low-temperature, HCl-modulated de novo method developed by Hupp and Farha and shown to contain large amounts of missing cluster defects, forming nanodomains of the reo phase with 8-connected clusters. In the extreme case of homoleptic UiO-67-TEMPO(100%), the material exists as an almost pure reo phase. Large voids due to missing clusters and linkers allowed these materials to accommodate up to 2 times more of bulky TEMPO substituents than theoretically predicted for the idealized structures and proved to be beneficial for catalytic activity. The TEMPO-appended MOFs were shown to be highly active and recyclable catalysts for selective aerobic oxidation of a broad range of primary and secondary alcohols under exceptionally mild conditions (room temperature, atmospheric pressure of air). The influence of various parameters, including the pore size and TEMPO content, on the catalytic activity was also comprehensively investigated.

NaOH alone can be a homogeneous catalyst for selective aerobic oxidation of alcohols in water

Sodium hydroxide (NaOH) has been an indispensable additive in the selective aerobic oxidation of alcohols/polyols in water for ketone and carboxylic acid syntheses over supported metal catalysts, including Au, though the exact function of NaOH remains far from clear. We disclose here that NaOH alone can independently serve as a homogeneous catalyst for the oxidation reactions. This conclusion is supported by rigorous investigations of the effects of NaOH alone (without the presence of any metal catalyst) on the reactivity of aqueous glycerol, ethylene glycol, 2-propanol, and ethanol and their product distribution. Computational results based on density functional theory are also provided to explain the experimentally measured reactivity order of the various alcohols and to generate insight into the molecular mechanisms for the oxidation reactions. Besides challenging existing knowledge about the function of NaOH in alcohol oxidation reactions, this study opens a new avenue for catalytic alcohol/polyol upgrading.

Improved activity of palladium nanoparticles using a sulfur-containing metal–organic framework as an efficient catalyst for selective aerobic oxidation in water

Synergism of thiophene and confinement of MOF with time of Pd entrance leads an efficient catalyst for oxidation in water.

Bimetallic Cu-Pd Nanoparticles Supported on Bio-silica as an Efficient Catalyst for Selective Aerobic Oxidation of Benzylic Alcohols

A new bimetallic heterogeneous catalyst consisting of copper and palladium nanoparticles supported on bio-silica is presented. The use of TEMPO as co-catalyst allowed the aerobic oxidation of primary benzylic alcohols into the corresponding aldehydes with excellent selectivity and good activity. The methodology could be applied to the oxidation of allylic and heterobenzylic alcohols. The catalyst is easy to prepare from commercial starting materials and can be recovered and reused without apparent loss of activity.