Catalyst For Oxidation Of Alcohols Research Articles

Electrochemical alcohol oxidation using a TEMPO nitroxide polymer as a homogeneous and surface‐confined catalyst

AbstractPolymers containing TEMPO moieties are effective catalysts for the electrochemical oxidation of alcohols. Such polymers, almost exclusively, are non‐commercial and are prepared using multi‐step synthetic procedures. Here we show that a commercially available TEMPO bearing polymer, Polyamine Immobilised Piperidinyl Oxyl (PIPO), is an effective homogeneous and surface‐confined polymeric catalyst for electrochemical alcohol oxidation at carbonaceous electrodes. We probe electrolytic conditions for effective and stable electrocatalytic alcohol oxidation showing that dichloromethane (DCM), containing tetrabutylammonium perchlorate (TBAP) and N‐methyl imidazole (NMI), is a suitable medium for homogeneous catalysis whilst carbonate buffer (pH 9.5) is better suited when PIPO is adsorbed at the electrode surface. These findings demonstrate the viability of PIPO as an effective and accessible catalyst for electrochemical alcohol oxidations.

Mesoporous silica-supported Ni–Co composite metal oxide as a heterogeneous catalyst for air oxidation of benzyl alcohols

A mesoporous silica-supported Ni–Co composite metal oxide has been synthesized and applied as an effective heterogeneous catalyst for the selective catalytic oxidation of benzyl alcohols. Various characterization methods were employed to confirm the successful synthesis of the catalysts and their nanostructure. The catalytic performances of these catalysts in the selective oxidation of substituted benzyl alcohols to aromatic aldehydes were systematically investigated using molecular oxygen from the air as the oxidant under atmospheric pressure. The NiCo@SBA-15 catalyst exhibited remarkable performance, achieving nearly 98 % conversion and almost complete selectivity at a temperature of 120 °C for 10 h, operating at 1 atm of air pressure. This catalytic performance can be attributed to the synergistic effect between Ni and Co ions, resulting in the generation of new surface-active sites in the catalyst. The catalyst also demonstrated favorable applicability and universality. Moreover, A plausible catalytic mechanism has been proposed involving the synergistic effect between bimetal species and oxygen vacancy.

Insight into the promotional effect of Ce doped in (FeCoNiCrMn)3O4 high entropy oxides for solvent-free aerobic oxidation of benzyl alcohol

It is desired but challenging to develop a non-noble metal catalyst for the selective oxidation of benzyl alcohol with O2 under solvent-free conditions. Herein, a series of Ce-doped high entropy oxides (Ce/HEOs) were prepared via co-precipitation and subsequent thermal treatment method. It was found that, the doping of Ce could remarkably promote the catalytic activity for selective oxidation of benzyl alcohol to benzaldehyde. The improved activity was ascribed to the good distribution of active Ce species, the increased oxygen vacancies, and the synergistic effect between CeO2 and high entropy oxides (HEOs). In addition, the surface oxygen of Ce/HEOs towards Ce displayed stronger reducibility compared to that of bare CeO2, endowing it stronger deprotonation ability towards benzyl alcohol during the reaction. The prepared catalyst exhibited satisfactory reusability and stability owing to the entropy-stabilized effect of HEOs and the interaction between CeO2 and HEOs, and negligible loss in catalytic activity was observed after seven runs. Besides, DFT calculations disclosed that, with the doping of Ce, the Ce/HEOs catalyst possessed stronger adsorption ability towards benzyl alcohol, and lower free energy was required for the rate-determining step during the whole oxidative reaction. This work gave some insights into the promotional effect of Ce doped into high entropy oxides for the solvent-free catalytic oxidation of benzyl alcohol.

Development of a Pd-xCNT-Ni-yCB composite catalyst to enhance the oxidation of various alcohols in alkali mediums

Developing a comprehensive strategy and superior catalysts for alcohol oxidation is essential for real applications of direct alcohol fuel cells. By adding palladium (Pd) onto the nickel (Ni) nanoparticles loaded on a mixed multiwalled carbon nanotubes (CNTs) and carbon black (CB) support by a reduction method with 10 wt% Pd and 10 wt% Ni, various weight ratios carbon compositions of Pd-xCNT-Ni-yCB catalyst materials (x and y = 1–2) were also studied. Well-dispersed Pd nanoparticles with average particle sizes of 3.3 and 5.5 nm were present on the 1CNT-Ni-2CB and 1CNT-2CB composite supports, respectively. X-ray photoelectron spectroscopy (XPS) analysis indicated that Pd exhibits a metallic palladium surface state with some fraction of NiO and Ni(OH)2 species. Alcohol oxidation e.g., methanol, ethanol, and iso-propanol in alkaline electrolytes was investigated by electrochemical measurements and analysis. Compared with single carbon catalysts, e.g., Pd-CNT and Pd-CB catalysts, in studies involving methanol, ethanol and isopropanol oxidation, most Pd-xCNT-Ni-yCB catalysts show high activity. The best performance obtained by Pd-1CNT-Ni-2CB could be related to the increased kinetics reaction and instantaneous presence of the bifunctional mechanism and electronic effect, resulting in a Pd and Ni alloy with a small amount of Ni(OH)2 in the xCNT-Ni-yCB composite support surfaces.

Synthesis of copper(ii) complex-functionalized Fe3O4@ISNA (ISNA = isonicotinic acid) as a magnetically recoverable nanomaterial: catalytic studies in alcohol oxidation and nitrophenol reduction, and TD-DFT studies

The synthesis of a magnetically separable nanocatalyst Fe3O4@ISNA@CuL1 used as a catalyst for oxidation of alcohols and reduction of nitrophenols.

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.

Switching of selectivity from benzaldehyde to benzoic acid using MIL-100(V) as a heterogeneous catalyst in aerobic oxidation of benzyl alcohol

A vanadium-centered metal organic framework [MIL-100(V)] was synthesized as a heterogeneous catalyst allowing to switch the selectivity from almost quantitative formation of benzaldehyde (Bz-CHO) to quantitative formation of benzoic acid...

Graphene as a Platform in Surface-Enhanced Infrared Absorption Spectroscopy (SEIRAS) for Amino-TEMPO Electro-Grafting

2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) has emerged as an environmentally benign catalyst for the electrochemical oxidation of primary and secondary alcohols to aldehydes and ketones (1). This simple organic free radical reagent possesses high activity, and versatility, and is one of the most promising alternatives to noble metal catalysts that were previously studied. The catalytic activity and reactivity of TEMPO is mostly studied in bulk solutions, for fuel cells, aqueous redox flow batteries and sensors (2, 3). For more practicality, various approaches were developed to immobilize TEMPO on active supports, such as anionic polyelectrolytes, and the electropolymerization of TEMPO-substituted pyrrole or thiophene (4, 5). However, these substrates suffer from instability, loss of catalytic activity, degradation of the polymer film in alkaline environment mostly used for TEMPO regeneration. One other way, is to use carbon-based substrates that are stable in aqueous acid and base environment, as well as non-aqueous solutions and have shown enhanced electrocatalytic behavior (6, 7).In this work, we studied the electro-grafting of amino-TEMPO on graphene using in-situ attenuated total reflection infrared absorption spectroscopy (ATR-IRAS). We observed that TEMPO is attached on the surface through covalent bonding between the amine and the graphene lattice, as previously reported (6, 7). While grafting was successfully demonstrated via the oxidation of the primary amine to a radical cation which reacted with the graphene surface, ATR-surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) provided additional spectral feature confirming TEMPO grafting through plasmon induced signal enhancement. Hickey, D. P.; Milton, R. D.; Chen, D.; Sigman, M. S.; Minteer, S. D., TEMPO-Modified Linear Poly(ethylenimine) for Immobilization-Enhanced Electrocatalytic Oxidation of Alcohols. ACS Catalysis 2015, 5 (9), 5519-5524. Mishra, A.; Kim, J.; Zorigt, M.; Romo, A. I. B.; Gaddam, R.; Braun, J. E.; Ziviani, D.; Rodríguez-López, J., Highly Selective TEMPO Catalyzed Bulk Electrooxidation of Isopropanol to Acetone for Application in Electrochemical Heat Pumping. ACS Sustainable Chemistry & Engineering 2023, 11 (16), 6241-6249. Elouarzaki, K.; Mandoc, L.-R. P.; Gorgy, K.; Holzinger, M.; Amarandei, C.-A.; Ungureanu, E.-M.; Cosnier, S., Synthesis and electrochemical characterization of original “TEMPO” functionalized multiwall carbon nanotube materials: Application to iron (II) detection. Electrochemistry Communications 2015, 60, 131-134. Belgsir, E. M.; Schäfer, H. J., Selective oxidation of carbohydrates on Nafion®–TEMPO-modified graphite felt electrodes. Electrochemistry Communications 2001, 3 (1), 32-35. Grimshaw, J.; Perera, S. D., Poly(pyrrole-pyromellitimide) modified electrodes. Journal of Electroanalytical Chemistry and Interfacial Electrochemistry 1990, 278 (1), 279-286. Barman, K.; Askarova, G.; Jia, R.; Hu, G.; Mirkin, M. V., Efficient Voltage-Driven Oxidation of Water and Alcohols by an Organic Molecular Catalyst Directly Attached to a Carbon Electrode. Journal of the American Chemical Society 2023, 145 (10), 5786-5794. Yuan, B.; Xu, C.; Zhang, D.; Zhang, R.; Su, H.; Guan, P.; Nie, J.; Fernandez, C., Electrografting of amino-TEMPO on graphene oxide and electrochemically reduced graphene oxide for electrocatalytic applications. Electrochemistry Communications 2017, 81, 18-23.

Performance scrutiny of spent lithium-ion batteries cathode material as a catalyst for oxidation of benzyl alcohol

The widespread use of Li-ion batteries (LIBs) in energy storage devices has resulted in the generation of additional waste which contains valuable metal ions and these metal ions are well known for their catalytic activities. The recovered black mass of cathode material was exposed to pretreatment with final calcination for 2 h at 800 0C. After the calcination, the material was subjected to structural characterization (XRD, FE-SEM, EDAX, and XPS). In the present work, we have used spent LIBs cathode material as a catalyst for the oxidation reaction of benzyl alcohol to benzoic acid. The catalytic activity of this recovered cathode material was found to be highly efficient showing 100% conversion of benzyl alcohol with >99% selectivity of benzoic acid with lower catalyst loading of even 2%.

Fe-Ni bimetallic supported on mordenite catalyst for selective oxidation of veratryl alcohol in a continuous reactor

Veratryl alcohol (VA) is preferentially oxidized to veratraldehyde (VADE) using a heterogeneous catalyst, which is more favoured in industries. Commercial mordenite (Ca,Na2,K2) Al2Si10O24·7H2O) was desilicated with NaOH and loaded with nickel and iron bimetal by the wet impregnation method. The synthesised Mordenite-Fe(5 %)/Ni(5–20 %) bimetallic catalyst, possessing active Bronsted acid sites, was employed to selectively oxidize the veratryl alcohol reaction. FT-IR, XRD, BET, HR-SEM, HR-TEM, and TPD were employed to determine the catalyst's textural attributes, morphology, chemical properties, and stability. Selective oxidation was performed over the catalysts using TBHP as an oxidant in a continuous reactor. To examine the most active catalyst among the four and to maximise the conversion and yield, the reaction conditions are optimised for various reaction parameters The reaction conditions were optimized by attaining 100 % conversion at temperature (90° C) for time (2 hr) and a maximum conversion of 97 % and a selectivity of 99 % at 10 bar pressure, WHSV (1.0 h−1) with acetonitrile solvent. The result of the study display that Fe (5 %) and Ni(15 %) impregnated on mordenite exhibits excellent catalytic stability with conversion (100 %) and selectivity (99 %) among the other catalysts. During regeneration, the conversion rate declined from 99.5 to 92.4.7 % and selectivity declined from 100 % to 96.2 % at the end of the seventh cycle. The high selectivity and stability of MOR-Fe(5 %)/Ni(15 %) imply that they might function properly as appropriate catalysts for the oxidation of aromatic alcohols. The advantages of the current synthesis are its cost-efficiency and eco-friendliness.

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.

4‐OH‐TEMPO radical grafted onto a novel polyaromatic ether sulfone containing carboxyl side chains as solid catalyst for alcohol oxidation

Abstract2,2,6,6‐Tetramethylpiperidinium‐nitroxide (TEMPO) is a mild and efficient catalyst, which is important in the industrial production of selective oxidation of alcohols to the corresponding aldehyde or ketone compounds. However, it is a challenge to recover the expensive TEMPO catalyst in homogeneous catalytic systems. In this study, a novel polymer‐supported catalyst was prepared using 4‐hydroxy‐2,2,6,6‐tetramethylpiperidin‐1‐oxy (4‐OH‐TEMPO) and polyaromatic ether sulfone (PAES). The successful grafting of 4‐OH‐TEMPO in PAES‐C was demonstrated by 1H nuclear magnetic resonance (1H NMR) and Fourier transform infrared (FT‐IR), load capacity can be calculated by elemental analysis (EA). BET and scanning electron microscopy (SEM) to depict the structure‐performance relationship. Herein, SEM images revealed the existence of porous structure. This structure can effectively adsorb NO molecules to form a PAES‐TEMPO/NOx catalytic system to selectively oxidize benzyl alcohol. The experimental results indicated the high activity, the subsequent benzyl alcohol oxidation cycle can reach more than 93% conversion without showing a large loss of selectivity. More importantly, the as‐prepared catalyst exhibited the attractive recyclability (recovery rate is 98%). After 10 consecutive runs, no significant loss of conversion and selectivity was observed (the conversion rate of benzyl alcohol was more than 93% and the selectivity was more than 95%). This study might provide some recommendation on the development of highly efficient catalysts for alcohol oxidation.

Improved Catalytic Performance toward Selective Oxidation of Benzyl Alcohols Originated from New Open-Framework Copper Molybdovanadate with a Unique V/Mo Ratio.

A new organic-inorganic hybrid open-framework molybdovanadate with mixed-valences of vanadium (V4+ /V5+ =4/3) and molybdenum (Mo5+ /Mo6+ =8/2) cations has been synthesized. The complex possesses the unique V/Mo ratio (7/10), fascinating 8-C topological network and 1D 4-MR channels (7.793 Å×6.699 Å). Importantly, its catalytic activities for the selective oxidation of benzyl alcohol to benzaldehyde (oxidant: H2 O2 , 30 wt %) have been well evaluated. The results indicated that it exhibited improved catalytic activities (conv.: 96.8 %) compared with the catalyst (Cpyr)5 PV2 Mo5 W5 O40 [conv.: 88.51 %, Cpyr=(C16 H32 C5 H4 N)+ )], high recyclability and structural stability. Moreover, the conversions and selectivities (conv.: 82.4-92.5 %; sele.: 91.5-95.7 %) of the substrates containing electron donating groups (-OH, -CH3 , -OCH3 and -Cl) were significantly higher than those of the substrate containing electron withdrawing group (-NO2 ) (conv. 67.4 %; sele.: 80.8 %). This is due to the fact that the -NO2 with a large Hammett substituent constant is not conducive to the generation of transition state products. The studies revealed the complex could act as a highly efficient heterogeneous catalyst in selective oxidation of benzyl alcohols.

Photocatalytic activity of CuBi2O4/WO3 p-n heterojunction photocatalysts in benzyl alcohol oxidation to benzaldehyde

CuBi2O4/WO3 (CBO/WO3) p-n heterojunction composite was synthesized by mechanical stirring and sonication for the selective oxidation of benzyl alcohol to benzaldehyde under visible light. Multiple characterization methods, including XRD, XPS, SEM, TEM, UV–vis DRS, BET, EIS and ESR, were used to investigate the origin of the excellent photocatalytic activity. The results of XRD, XPS, SEM, and TEM revealed that CBO/WO3 catalyst was successfully synthesized. Benzaldehyde selectivity of over 99 % and benzyl alcohol conversion of 54.8 % were obtained under an optimized condition using 50 mg of 40-CBO/WO3 (40 stood for the mass percentage of CBO in CBO and WO3.). DFT results showed that ∆Eads values of benzyl alcohol were − 0.51, − 0.66 and − 0.88 eV on CBO, WO3 and CBO/WO3. The oxidation of benzyl alcohol occurred more easily on the surface of CBO/WO3. Meanwhile, the stability of 40-CBO/WO3 was investigated. After 5 repeated experiments, a high conversion was still maintained, indicating its potential in practical application. A possible mechanism of benzyl alcohol to benzaldehyde was proposed through the capturing experiment of active species. This work successfully designed an efficient p-n heterojunction composite catalyst for selective oxidation of benzyl alcohol. Replacing traditional thermal synthesis with selective photocatalysis can promote more environmentally friendly processes.

Development of sustainable green catalysts for oxidation of alcohols via decorated palladium nanoparticles on magnetic carbon nanotube/MOF

Using a straightforward method, this study fabricated an eco-friendly low-cost magnetic nanocomposite consisting of magnetic carbon nanotube/MOF as a stabilizer. Pd nanoparticles (Pd NPs) were then decorated on the designed magnetic carbon nanotube/MOF microspheres, and the resulting magnetic carbon nanotube/MOF/Pd NPs nanocomposite were employed as heterogeneous catalysts in Aerobic oxidation of primary and secondary alcohols. The attractiveness of this work is in the selective oxidation of several types of active and inactive alcohol substrates. The most important feature of this catalyst is its successful recovery and simple separation repeatedly without reducing its activity and selectivity. The active surface area of this Nanocatalyst is very large due to its structural properties, and as a result, it provides more available catalytic sites, which increases its activity. The identification techniques used to investigate the structural properties of this Nanocatalyst confirm its successful synthesis and appropriate palladium loading into the catalyst sites. The oxidation of alcohols was determined by Gas Chromatography (GC). The 100% selectivity, excellent turnover number (TON), high yield, almost complete and fast conversion of alcohol to the desired aldehydes and ketones without more oxidation, and easy and no-trouble isolation of product and catalyst are outstanding features of this catalytic system. The use of picolinaldehyde lead to the high loading of Pd NPs, reducing the catalyst content needed for the reaction. Regarding the high catalyst loading, using a small amount of catalyst is recommended for proceeding with the reaction efficiently.

Polyhedral Coordination Determined Co‐O Activity for Electrochemical Oxidation of Biomass Alcohols

AbstractEarth‐abundant transition metal oxides are promising electrocatalysts for oxidation of biomass alcohols. Here, CoO and Co3O4 are selected as representative cobalt oxide catalysts and grown on carbon fiber paper (CFP) electrodes to reveal the interplay between electronic structure and catalytic activity of catalysts for oxidation of glycerol, diols, and monohydric alcohols. In situ electrochemical tests elucidate that the CoO/CFP electrode has lower interfacial impedance, higher charge transfer, faster oxidation rate, and thereby the higher catalytic activity for alcohol oxidation than the Co3O4/CFP electrode. Especially for glycerol oxidation, the CoO/CFP electrode only requires 1.32 V to reach 10 mA cm−2, the potential is 120 mV lower than that for the Co3O4/CFP electrode. The CoO/CFP electrode can also produce value‐added products such as formate, acetate, and glycolate with high selectivity and efficiency at low energy consumptions from oxidation of biomass alcohols. Theoretical calculations further confirm the dominant role of octahedrally coordinated Co‐O sites in adsorption, activation, and oxidation of C3‐C1 alcohols. This work sheds light on the design of highly efficient transition metal oxide catalysts for oxidation of alcohols by populating octahedral sites in the crystal structure.

Copper Nanoparticles Supported on ZIF-8: Comparison of Cu(II) Reduction Processes and Application as Benzyl Alcohol Oxidation Catalysts.

We report the synthesis of a stable heterogeneous catalyst based on copper metal nanoparticles with oxidized surface supported on ZIF-8 for the oxidation of benzyl alcohol under mild temperature and using air as a sustainable oxygen source as well as for the implementation of the tandem "one-pot" catalytic system allowing the sustainable synthesis of benzylidene malononitrile. The influence of the reduction process applied to form the nanoparticle upon the catalyst texture and its performances was extensively examined. After ZIF-8 impregnation with a copper chloride precursor, the reduction of cupric ions into Cu0 nanoparticles was carried out according to two procedures: (i) by soaking the solid into a solution of NaBH4 and (ii) by submitting it to a flow of gaseous H2 at 340 °C. The in-depth physicochemical characterization and comparison of the resulting two types of Cu/ZIF-8 materials reveal significant differences: the reduction with NaBH4 led to the formation of 16 nm sized Cu0 nanoparticles (NP) mainly localized on the external surface of the ZIF-8 crystals together with ZnO nanocrystallites, while the reduction under H2 flow resulted in Cu0 nanoparticles with a mean size of 22 nm embedded within the bulk of ZIF-8 crystals. More, when NaBH4 was used to reduce cupric ions, ZnO particles were highlighted by high-resolution microcospy imaging. Formation of ZnO impurities was confirmed by the photoluminescence analysis of ZIF-8 after NaBH4 treatment. In contrast, ZnO was not detected on ZIF-8 treated with H2. Both types of Cu0 NPs supported on ZIF-8 were found to be active as catalysts toward the aerobic oxidation of benzyl alcohol under moderate temperature (T < 80 °C) and using air as a sustainable O2 source. Benzaldehyde yield of 66% and selectivity superior to 90% were obtained with the Cu/ZIF-8 catalyst prepared under H2 flow after 24 h under these conditions. The same material could be recycled 5 times without loss of activity, unlike the catalysts synthesized with NaBH4, as a result of the leaching of the surface copper NPs over the consecutive catalytic cycles. Finally, the most stable catalyst was successfully implemented in a tandem "one-pot" catalytic system associating benzyl alcohol oxidation and Knoevenagel condensation to synthesize benzylidene malononitrile.

Synthesis and characterization of N4-donor Schiff base copper(II) immobilized on superparamagnetic Fe3O4@SiO2 and its use as a recyclable catalyst for oxidation of alkenes, alcohols, and determination of antibacterial activity

N4-donor Schiff base copper(II) nanoparticles were easily prepared through surface modification of silica-coated magnetite nanoparticles (Fe3O4@SiO2) with pyrrole 2-carbaldehyde Schiff base and a subsequent reaction with Cu(CH3COO)2.H2O in ethanolic solution. This nanocatalyst was characterized using thermogravimetric analysis (TGA), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), and magnetization. Efficient oxidation of alkenes and alcohols was carried out over the Schiff base copper(II) nanoparticles. Catalytic tests showed that the catalyst was particularly effective for the oxidation of α-methyl styrene, norbornene, benzyl alcohol, and benzohydrol. The results showed that acetophenone, 2-norbornanone, benzoic acid, and benzophenone with selectivity values of 88, 100, 100, and 100, respectively, were obtained. The heterogeneous catalyst of N4-donor Schiff base copper(II) offers advantages such as ease of product separation, catalyst recycling, and ease of preparation. Antibacterial tests against two gram-positive and two gram-negative bacterial species found that the bacteria stopped growing in the catalyst medium.

Core–Shell Catalysts for Conventional Oxidation of Alcohols: A Brief Review

This review highlights recent research on the application of core–shell structured materials as catalysts in the oxidation of alcohols to value-added products, such as benzaldehyde, acetophenone, benzophenone, cinnamaldehyde, and vanillin, among others. While the application of various unconventional energy inputs (such as microwave and ultrasound irradiation) was reported, this paper focuses on conventional heating. The oxidation of homocyclic aromatic, heterocyclic aromatic, aliphatic, and alicyclic alcohols catalyzed by core–shell composite catalysts is addressed. This work also highlights some unique advantages of core–shell nanomaterial catalysis, namely the flexibility of combining individual functions for specific purposes as well as the effect of various parameters on the catalytic performance of these materials.

Aerobic oxidation of benzylic alcohols catalysed by new (aryl‐BIAN)copper(I) complexes: Their synthesis and structural characterization

A new neutral dimeric Ar‐BIAN Cu(I) complex (where Ar‐BIAN = bis(aryl‐imino)acenaphthene) of formulation [CuBr(4‐iPrC6H4‐BIAN)]2 (2) was obtained by reacting CuBr and ligand 4‐iPrC6H4‐BIAN (L2) in refluxing acetonitrile under an argon atmosphere. When the ligand used was 2,4,6‐Me3C6H2‐BIAN (L1), we obtained 1 in which the expected dimer (1a) is present, but we could also observe, in solution, the presence of the bis‐chelate dimer [Cu(2,4,6‐Me3C6H2‐BIAN)2][CuBr2] (1b) bearing CuBr2− as counter‐ion; attempts to separate them failed. When the ligand used was 2‐iPrC6H4‐BIAN (L3), we obtained 3 in which the expected dimer (3a) is in equilibrium, in solution, with its bis‐chelate isomer [Cu(2‐iPrC6H4‐BIAN)2][CuBr2] (3b). The solid‐state molecular structures of compounds 2 and 3b were determined by single crystal X‐ray diffraction. The electrochemical behaviour of complexes: 1 (1a, and 1b), 2, and 3 (3a and 3b) and the known compound [Cu(2‐iPrC6H4‐BIAN)2][BF4] (7) were investigated by cyclic voltammetry. The new complexes 1 (1a, 1b), 2, and 3 (3a, 3b) were tested as catalysts for the aerobic oxidation of benzylic alcohols into aldehydes; they all catalyse the reaction, with good results; the catalytic studies were extended to the similar known complexes [CuBr(2,6‐iPr2C6H3‐BIAN)]2 (4), [CuI(2,6‐iPr2C6H3‐BIAN)]2 (5), [CuCl(2,6‐iPr2C6H3‐BIAN)]2 (6) and (7), in order to study the effect of different bridging halides or counter ions in the catalytic activity. We found that compound 4 exhibited a high catalytic activity comparable to the best results published so far. The oxidation products, benzaldehydes, were detected and further confirmed by NMR spectroscopy, and the conversion rate was determined after GC‐FID analysis.