Catalyst For Aerobic Oxidation Research Articles

Three‐Dimensional Radical Covalent Organic Frameworks as Highly Efficient and Stable Catalysts for Selective Oxidation of Alcohols

AbstractWith excellent designability, large accessible inner surface, and high chemical stability, covalent organic frameworks (COFs) are promising candidates as metal‐free heterogeneous catalysts. Here, we report two 3D radical‐based COFs (JUC‐565 and JUC‐566) in which radical moieties (TEMPO) are uniformly decorated on the channel walls via a bottom‐up approach. Based on grafted functional groups and suitable regular channels, these materials open up the application of COFs as highly efficient and selective metal‐free redox catalysts in aerobic oxidation of alcohols to relevant aldehydes or ketones with outstanding turn over frequency (TOF) up to 132 h−1, which has exceeded other TEMPO‐modified catalytic materials tested under similar conditions. These stable COF‐based catalysts could be easily recovered and reused for multiple runs. This study promotes potential applications of 3D functional COFs anchored with stable radicals in organic synthesis and material science.

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.

Recyclable Pd‐based polysaccharide catalyst for aerobic oxidation of benzyl alcohol

AbstractPalladium acetate that was heterogenized together with triphenylphosphine trisulfonate ligand on renewable polysaccharides was employed in the aerobic oxidation of benzyl alcohol in three representative solvents—hexane, ethyl acetate, and ethanol. Solvent polarity was found to affect the reaction rate, as both the solubility of benzyl alcohol and oxygen depend on the nature of the solvent. The conversion rate was decreased in the order of hexane > ethanol > ethyl acetate (conversion rates in the presence of the heterogenized iota‐based catalyst after 24 h of reaction were 38, 20, and 15%, respectively). In addition, the nature of the polysaccharide, that is, the type and numbers of functional groups on its backbone, also affected the reaction rate, where xanthan gum yielded the highest conversion rate of 58% in hexane. Finally, though hexane was found to be the preferred solvent for the heterogeneous system, catalytic performance in hexane decreased during recycling while in ethanol it increased due to the formation of palladium nanoparticles. To reveal the structural changes undergone by the catalyst during the reaction, several techniques were used, including energy dispersive X‐ray spectrometry‐scanning electronic microscopy, X‐ray photoelectron spectroscopy, Transition electronic microscopy, and thermal gravimetric analysis. This simple and straightforward heterogenization procedure can be also used for immobilization of different other metal complexes in variety of organic reactions.

Highly dispersive Pd nanoparticles decorated strontium niobate nanosheets: Efficient and recyclable catalyst for base-free aerobic oxidation of benzyl alcohols in water

2D perovskite Sr2Nb3O10 (SNO) nanosheets were synthesized by cation exchange-assisted liquid exfoliation and applied as supports for the immobilization of palladium (Pd) nanoparticles through the electrostatic assembly with Pd(NH3)42+ precursors and successive in-situ photoreduction. Pd nanoparticles with an average diameter of 9.22 nm are uniformly dispersed on the surface of strontium niobate nanosheets. The obtained nanohybrid Pd-SNO could serve as an efficient heterogeneous catalyst for the atmospheric pressure oxidation of benzyl alcohol to benzaldehyde by using air as an oxidizing agent and water as the sole solvent at low temperature (80 °C). Furthermore, the catalyst could be easily separated from the reaction mixture by simple centrifugation and reused five times without significant degradation in catalytic activity under the investigated conditions. We believe that the synthetic strategy described in this work is a feasible means of developing effective noble metal/layered transition metal oxide hybrid catalysts for organic reactions.

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.

Aerobic Alcohol Oxidation by a Zeolitic Octahedral Metal Oxide based on Iron Vanadomolybdates Under Mild Conditions

AbstractZeolitic octahedral metal oxides are fully‐inorganic crystalline materials with the multi‐component redox property and the intrinsic microporosity. The redox active zeolitic iron vanadomolybdate acts as a catalyst for aerobic oxidation of primary aromatic alcohols. Molecular oxygen is able to be activated in the material due to the confinement effect of the micropore and the unique redox property of the framework. Different primary aromatic alcohols are oxidized by the material, and high alcohol conversion and aldehyde selectivity are achieved. The material is stable and able to be reused for 5 times without loss of activity.

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.

Strategies in Metal–Organic Framework‐based Catalysts for the Aerobic Oxidation of Alcohols and Recent Progress

Metal–organic frameworks (MOFs), which are porous inorganic–organic hybrid materials, act as versatile catalyst platforms for various organic transformations. In particular, the aerobic oxidation of alcohols to the corresponding aldehydes (or ketones) has been extensively studied using various MOFs and their analogs. In this account, we summarize the performance of MOF‐based catalysts for the aerobic oxidation of alcohols based on the position of the catalytic species and the type of functionalization. Moreover, recent advances in MOF‐based catalysts for aerobic oxidation are discussed in terms of catalytic efficiency and substrate size discrimination.

Metallophthalocyanines as Catalysts in Aerobic Oxidation

The first remarkable property associated to metallophthalocyanines (MPcs) was their chemical “inertness”, which made and make them very attractive as stable and durable industrial dyes. Nevertheless, their rich redox chemistry was also explored in the last decades, making available a solid and detailed knowledge background for further studies on the suitability of MPcs as redox catalysts. An overlook of MPcs and their catalytic activity with dioxygen as oxidants will be discussed here with a special emphasis on the last decade. The mini-review begins with a short introduction to phthalocyanines, from their structure to their main features, going then through the redox chemistry of metallophthalocyanines and their catalytic activity in aerobic oxidation reactions. The most significant systems described in the literature comprise the oxidation of organosulfur compounds such as thiols and thiophenes, the functionalization of alkyl arenes, alcohols, olefins, among other substrates.

Tailoring the electron density of cobalt oxide clusters to provide highly selective superoxide and peroxide species for aerobic cyclohexane oxidation.

The catalytic aerobic cyclohexane oxidation to cyclohexanol and cyclohexanone (KA oil) is an industrially relevant reaction. This work is focused on the synthesis of tailor-made catalysts based on the well-known Co4O4 core in order to successfully deal with cyclohexane oxidation reaction. The catalytic activity and selectivity of the synthesized catalysts can be correlated with the electronic density of the cluster, modulated by changing the organic ligands. This is not trivial in cyclohexane oxidation. Furthermore, the reaction mechanism is discussed on the basis of kinetics and spin trapping experiments, confirming that the electronic density of the catalyst has a clear influence on the distribution of the reaction products. In addition, in situ Raman spectroscopy was used to characterize the oxygen species formed on the cobalt cluster during the oxidation reaction. Altogether, it can be concluded that the catalyst with the highest oxidation potential promotes the formation of peroxide and superoxide species, which is the best way to oxidize inactivated CH bonds in alkanes. Finally, based on the results of the mechanistic studies, the contribution of these cobalt oxide clusters in each single reaction step of the whole process has been proposed.

MOF-Zn-NHC as an efficient N-heterocyclic carbene catalyst for aerobic oxidation of aldehydes to their corresponding carboxylic acids via a cooperative geminal anomeric based oxidation.

As an efficient heterogenous N-heterocyclic carbene (NHC) catalyst, MOF-Zn-NHC was used in the aerobic oxidation of aryl aldehydes to their corresponding carbocyclic acids via an anomeric based oxidation. Features such as mild reaction conditions and no need for a co-catalyst or oxidative reagent can be considered as the major advantages of the presented method in this study.

Magnetic spent coffee ground as an efficient and green catalyst for aerobic oxidation of alcohols and tandem oxidative Groebke–Blackburn–Bienaymé reaction

In this work, magnetic spent coffee ground as a green, inexpensive, and abundant material was synthesized and characterized by a variety of techniques, including X-ray diffraction pattern, thermal gravimetric analysis, scanning electron microscopy, energy-dispersive spectroscopy, inductively coupled plasma optical emission spectrometry, and Fourier transform infrared spectroscopy. The magnetic spent coffee ground was successfully utilized as a catalyst in aerobic oxidation of primary and secondary benzylic alcohols and tandem oxidative Groebke–Blackburn–Bienayme reaction.

Water-Resistant Pt Sites in Hydrophobic Mesopores Effective for Low-Temperature Ethylene Oxidation

The structure–activity relationship of silica-supported Pt catalysts in aerobic oxidation of 50 ppm ethylene was studied at 0 °C with a fixed-bed flow reactor and in situ characterization technique...

Eco-Friendly and Solvent-Less Mechanochemical Synthesis of ZrO2–MnCO3/N-Doped Graphene Nanocomposites: A Highly Efficacious Catalyst for Base-Free Aerobic Oxidation of Various Types of Alcohols

In recent years, the development of green mechanochemical processes for the synthesis of new catalysts with higher catalytic efficacy and selectivity has received manifest interest. In continuation of our previous study, in which graphene oxide (GRO) and highly reduced graphene oxide (HRG) based nanocomposites were prepared and assessed, herein, we have explored a facile and solvent-less mechanochemical approach for the synthesis of N-doped graphene (NDG)/mixed metal oxide (MnCO3–ZrO2) ((X%)NDG/MnCO3–ZrO2), as the (X%)NDG/MnCO3–ZrO2 nano-composite was synthesized using physical grinding of separately synthesized NDG and pre-calcined (300 °C) MnCO3–ZrO2 via green milling method. The structures of the prepared materials were characterized in detail using X-ray powder diffraction (XRD), Field Emission Scanning Electron Microscope (FESEM), Energy Dispersive X-Ray Analysis (EDX), Fourier-transform infrared spectroscopy (FTIR), Raman, Thermogravimetric analysis (TGA), and N2 adsorption-desorption isotherm analysis. Besides, the obtained nanocomposites were employed as heterogeneous oxidation catalyst for the alcohol oxidation using green oxidant O2 without involving any surfactants or bases. The reaction factors were systematically studied during the oxidation of benzyl alcohol (PhCH2OH) as the model reactant to benzaldehyde (PhCHO). The NDG/MnCO3–ZrO2 exhibits premium specific activity (66.7 mmol·g−1·h−1) with 100% conversion of PhCH2OH and > 99.9% selectivity to PhCHO after only 6 min. The mechanochemically prepared NDG based nanocomposite exhibited notable improvement in the catalytic efficacy as well as the surface area compared to the pristine MnCO3–ZrO2. Under the optimal circumstances, the NDG/MnCO3–ZrO2 catalyst could selectively catalyze the aerobic oxidation of a broad array of alcohols to carbonyls with full convertibility without over-oxidized side products like acids. The NDG/MnCO3–ZrO2 catalyst were efficiently reused for six subsequent recycling reactions with a marginal decline in performance and selectivity.

The Role of Co-ZSM-5 Catalysts in Aerobic Oxidation of Ethylbenzene

Various forms of cobalt catalysts have been studied extensively for selective aerobic oxidation of hydrocarbons. However, it remains unclear whether cobalt can directly activate molecular oxygen under mild reaction conditions. Here we investigated the catalytic roles of cobalt in ethylbenzene oxidation with and without a hydroperoxide initiator. The contribution of different cobalt species was studied by varying the metal loading on Co-impregnated ZSM-5 samples. Quantitative EPR was used to determine the impact of cobalt catalysts on the free radical concentrations. This work provided strong evidence that cobalt, in several different forms, catalyzes hydrocarbon oxidation by facilitating peroxy bond cleavage, instead of direct oxygen activation.

Theoretical Investigation of the Heterojunction Effect on the Catalytic Activity and Selectivity of an Au@NiO Core–Shell Catalyst in Aerobic Oxidation

Numerous experimental reports have addressed the advantages of the Au@NiO core-shell catalyst in the synthesis of methyl methacrylate. However, its high activity toward the oxidation of 1-methoxy-2...

Utilization of biomass waste: Facile synthesis high nitrogen-doped porous carbon from pomelo peel and used as catalyst support for aerobic oxidation of 5-hydroxymethylfurfural

The oxidation of 5-hydroxylmethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) is a sustainable and promising method for the preparation of bio-derived aromatic polyesters. Nitrogen doped carbon material is an effective catalyst support in preparing supported nanoparticle metal catalysts in heterogeneous reactions. In this work, by pyrolysis of bio-waste carbon material, pomelo peel, under 800 °C flowing NH3, high nitrogen (up to 11.4 wt%) doped porous carbon material (NC) was facilely obtained. Pt nanoparticles (NPs) can be uniformly dispersed on NC surface and stabilized by the doped nitrogen dopant. Supported Pt NPs by NC-800 (Pt/NC-800) was proved to be an efficient catalyst in aerobic oxidation of HMF into FDCA. Control experiments show that the oxidation of 5-hydrox-ymethyl-2-furancarboxylic acid (HMFCA) to 5-formyl-2-furancarboxylic acid (FFCA) by supported Pt NPs was the key step to determine the oxidation rate of HMF to FDCA. With controlled experiment results and previous reports, a catalytic mechanism involving water, molecular O2, hydroxyl ions and Pt NPs was given and explained well of the phenomenon of high HMFCA concentration accumulation during reaction.

Pickering HIPEs derived hierarchical porous nitrogen-doped carbon supported bimetallic AuPd catalyst for base-free aerobic oxidation of HMF to FDCA in water

As an important renewable alternative to the production of petroleum-derived terephthalic acid, selective aerobic oxidation of biomass derivative 5-hydroxymethylfurfural (HMF) into high value-added 2,5-furandicarboxylic acid (FDCA) is attracting increasing attention. Herein, a novel hierarchical porous nitrogen-doped carbon (NC) supported bimetallic AuPd catalyst was synthesized by Pickering high internal phase emulsions (Pickering HIPEs) templating method, subsequent carbonization and the sol-curing technique. By varying Pickering HIPEs parameter, nitrogen-doped content and the loaded AuPd nanoparticles, AuxPdy/NC catalysts with adjustable porous structure and basicity were obtained. Benefiting from the synergistic effects of the high basicity of NC support and efficient bimetallic AuPd catalyst, tandem oxidation of HMF to FDCA reactions can be carried out under base-free condition in water, which makes the biomass transformation process environmental friendliness and economic. And the highest yield of FDCA at 96.7% was achieved under the optimal reaction conditions. Regeneration test revealed the obtained AuxPdy/NC catalyst was recovered and reused at least five times without significant loss of catalytic activity. The present work offers a versatile strategy for developing nitrogen-doped carbon supported highly efficient bimetallic catalysts with hierarchical porous structure and adjusting basicity for a wide range of base-free catalytic oxidation in water.