Theoretical study on the mechanism of alcohol photooxidation on Nb2O5 surface

Theoretical modeling of the solid-state photocatalysis is one of the important issues as various useful photocatalysts have been developed to date. In this work, we investigated the mechanism of the alcohol photooxidation on niobium oxide (Nb2O5) which was experimentally developed, using the density functional theory (DFT)/time-dependent (TD)DFT calculations based on the cluster model. The alcohol adsorption and the first hydrogen transfer from hydroxy group to surface occur in the ground state, while the second hydrogen transfer from CH proceeds in the excited states during the photoirradiation of UV or visible light. The spin crossing was identified and the low-lying triplet states were solved for the reaction pathway. The photoabsorption in the visible light region was characterized as the charge transfer transition from O 2p of alcohol to Nb 4d of the Nb2O5 surface. The spin density and the natural population analysis indicated the generation of spin density in the moiety of carbonyl compound and its dissipation to the interface of the surface, which partly explains the electron paramagnetic resonance measurement. It was confirmed that the rate determining step is the desorption of carbonyl compound and water molecule in agreement with the experimental rate equation analysis. The present findings with the theoretical modeling will provide useful information for the further studies of the solid-state photocatalysis.

Dye-Sensitized Photocatalysis: Hydrogen Evolution and Alcohol-to-Aldehyde Oxidation without Sacrifical Electron Donor

There is a growing interest in developing dye-sensitized photocatalytic systems (DSPs) to produce molecular hydrogen (H2 ) as alternative energy source. To improve the sustainability of this technology, we replaced the sacrificial electron donor (SED), typically an expensive and polluting chemical, with an alcohol oxidation catalyst. This study demonstrates the first dye-sensitized system using a diketopyrrolopyrrole dye covalently linked to 2,2,6,6-tetramethyl-1-piperidine-N-oxyl (TEMPO) based catalyst for simultaneous H2 evolution and alcohol-to-aldehyde transformation operating in water with visible irradiation.

Strain and Shell Thickness Engineering in Pd3 Pb@Pt Bifunctional Electrocatalyst for Ethanol Upgrading Coupled with Hydrogen Production

The ethanol oxidation reaction (EOR) is an attractive alternative to the sluggish oxygen evolution reaction in electrochemical hydrogen evolution cells. However, the development of high-performance bifunctional electrocatalysts for both EOR and hydrogen evolution reaction (HER) is a major challenge. Herein, the synthesis of Pd3 Pb@Pt core-shell nanocubes with controlled shell thickness by Pt-seeded epitaxial growth on intermetallic Pd3 Pb cores is reported. The lattice mismatch between the Pd3 Pb core and the Pt shell leads to the expansion of the Pt lattice. The synergistic effects between the tensile strain and the core-shell structures result in excellent electrocatalytic performance of Pd3 Pb@Pt catalysts for both EOR and HER. In particular, Pd3 Pb@Pt with three Pt atomic layers shows a mass activity of 8.60 A mg-1 Pd+Pt for ethanol upgrading to acetic acid and close to 100% of Faradic efficiency for HER. An EOR/HER electrolysis system is assembled using Pd3 Pb@Pt for both the anode and cathode, and it is shown that low cell voltage of 0.75 V is required to reach a current density of 10 mA cm-2 . The present work offers a promising strategy for the development of bifunctional catalysts for hybrid electrocatalytic reactions and beyond.

Pairing Electrocarboxylation of Unsaturated Bonds with Oxidative Transformation of Alcohol and Amine

A parallel paired electrosynthetic method, coupling electrocarboxylation incorporating CO2 into ketone, imine, and alkene with alcohol oxidation or oxidative cyanation of amine, was developed for the first time. Various carboxylic acids as well as aldehyde/ketone or α-nitrile amine were prepared at the cathode and anode respectively in a divided cell. Its utility and merits on simultaneously achieving high atom-economic CO2 utilization, elevated faradaic efficiency (FE, total FE of up to 166 %), and broad substrate scope were demonstrated. The preparation of pharmaceutical intermediates for Naproxen and Ibuprofen via this approach proved its potential application in green organic electrosynthesis.

Cu(II) and Mn(II) Anchored on Functionalized Mesoporous Silica with Schiff Bases: Effects of Supports and Metal-Ligand Interactions on Catalytic Activity

New series of Cu(II) and Mn(II) complexes with Schiff base ligands derived from 2-furylmethylketone (Met), 2-furaldehyde (Fur), and 2-hydroxyacetopheneone (Hyd) have been synthesized in situ on SBA-15-NH₂, MCM-48-NH₂, and MCM-41-NH₂ functionalized supports. The hybrid materials were characterized by X-ray diffraction, nitrogen adsorption-desorption, SEM and TEM microscopy, TG analysis, and AAS, FTIR, EPR, and XPS spectroscopies. Catalytic performances were tested in oxidation with the hydrogen peroxide of cyclohexene and of different aromatic and aliphatic alcohols (benzyl alcohol, 2-methylpropan-1-ol, and 1-buten-3-ol). The catalytic activity was correlated with the type of mesoporous silica support, ligand, and metal-ligand interactions. The best catalytic activity of all tested hybrid materials was obtained in the oxidation of cyclohexene on SBA-15-NH₂-MetMn as a heterogeneous catalyst. No leaching was evidenced for Cu and Mn complexes, and the Cu catalysts were more stable due to a more covalent interaction of the metallic ions with the immobilized ligands.

Radial Nano-Heterojunctions Consisting of CdS Nanorods Wrapped by 2D CN:PDI Polymer with Deep HOMO for Photo-Oxidative Water Splitting, Dye Degradation and Alcohol Oxidation

Solar energy harvesting using semiconductor photocatalysis offers an enticing solution to two of the biggest societal challenges, energy scarcity and environmental pollution. After decades of effort, no photocatalyst exists which can simultaneously meet the demand for excellent absorption, high quantum efficiency and photochemical resilience/durability. While CdS is an excellent photocatalyst for hydrogen evolution, pollutant degradation and organic synthesis, photocorrosion of CdS leads to the deactivation of the catalyst. Surface passivation of CdS with 2D graphitic carbon nitrides (CN) such as g-C₃N₄ and C₃N₅ has been shown to mitigate the photocorrosion problem but the poor oxidizing power of photogenerated holes in CN limits the utility of this approach for photooxidation reactions. We report the synthesis of exfoliated 2D nanosheets of a modified carbon nitride constituted of tris-s-triazine (C₆N₇) linked pyromellitic dianhydride polydiimide (CN:PDI) with a deep oxidative highest occupied molecular orbital (HOMO) position, which ensures sufficient oxidizing power for photogenerated holes in CN. The heterojunction formed by the wrapping of mono-/few layered CN:PDI on CdS nanorods (CdS/CN:PDI) was determined to be an excellent photocatalyst for oxidation reactions including photoelectrochemical water splitting, dye decolorization and the photocatalytic conversion of benzyl alcohol to benzaldehyde. Extensive structural characterization using HR-TEM, Raman, XPS, etc., confirmed wrapping of few-layered CN:PDI on CdS nanorods. The increased photoactivity in CdS/CN:PDI catalyst was ascribed to facile electron transfer from CdS to CN:PDI in comparison to CdS/g-C₃N₄, leading to an increased electron density on the surface of the photocatalyst to drive chemical reactions.

Subnanoscale Dual-Site Pd-Pt Layers Make PdPtCu Nanocrystals CO-Tolerant Bipolar Effective Electrocatalysts for Alcohol Fuel Cell Devices

Finding a high-performance low-Pt bipolar electrocatalyst in actual direct alcohol fuel cells (DAFCs) remains challenging and desirable. Here, we developed a crystalline PdPtCu@amorphous subnanometer Pd-Pt "dual site" layer core-shell structure for the oxygen reduction reaction (ORR) and alcohol (methanol, ethylene glycol, glycerol, and their mixtures) oxidation reaction (AOR) in an alkaline electrolyte (denoted D-PdPtCu). The prepared D-PdPtCu/C achieved a direct 4-electron ORR pathway, a full oxidation pathway for AOR, and high CO tolerance. The ORR mass activity (MA) of D-PdPtCu/C delivered a 52.8- or 59.3-fold increase over commercial Pt/C or Pd/C, respectively, and no activity loss after 20000 cycles. The D-PdPtCu/C also exhibited much higher AOR MA and stability than Pt/C or Pd/C. Density functional theory revealed the intrinsic nature of a subnanometer Pd-Pt "dual site" surface for ORR and AOR activity enhancement. The D-PdPtCu/C as an effective bipolar electrocatalyst yielded higher peak power densities than commercial Pt/C in actual DAFCs.

Copper Cobalt Selenide as a Bifunctional Electrocatalyst for the Selective Reduction of CO2 to Carbon-Rich Products and Alcohol Oxidation

Copper cobalt selenide, CuCo2Se4, has been identified as an efficient catalyst for electrocatalytic CO2 reduction, exhibiting high selectivity for carbon-rich and value-added products. Achieving product selectivity is one of the primary challenges for CO2 reduction reactions, and the catalyst surface plays a pivotal role in determining the reaction pathway and, more importantly, the intermediate adsorption kinetics leading to C1- or C2+-based products. In this research, the catalyst surface was designed to optimize the adsorption of the intermediate CO (carbonyl) group on the catalytic site such that its dwell time on the surface was long enough for further reduction to carbon-rich products but not strong enough for surface passivation and poisoning. CuCo2Se4 was synthesized through hydrothermal method, and the assembled electrode showed the electrocatalytic reduction of CO2 at various applied potentials ranging from -0.1 to -0.9 V vs RHE. More importantly, it was observed that the CuCo2Se4-modified electrode could produce exclusive C2 products such as acetic acid and ethanol with 100% faradaic efficiency at a lower applied potential (-0.1 to -0.3 V), while C1 products such as formic acid and methanol were obtained at higher applied potentials (-0.9 V). Such high selectivity and preference for acetic acid and ethanol formation highlight the novelty of this catalyst. The catalyst surface was also probed through density functional theory (DFT) calculations, and the high selectivity for C2 product formation could be attributed to the optimal CO adsorption energy on the catalytic site. It was further estimated that the Cu site showed a better catalytic activity than Co; however, the presence of neighboring Co atoms with the residual magnetic moment on the surface and subsurface layers influenced the charge density redistribution on the catalytic site after intermediate CO adsorption. In addition to CO2 reduction, this catalytic site was also active for alcohol oxidation producing formic or acetic acid from methanol or ethanol, respectively, in the anodic chamber. This report not only illustrates the highly efficient catalytic activity of CuCo2Se4 for CO2 reduction with high product selectivity but also offers a proper insight of the catalyst surface design and how to obtain such high selectivity, thereby providing knowledge that can be transformative for the field.

Electronic Tuning of Gold Nanoparticle Active Sites for Reduction Catalysis

Electronic tuning of active sites in heterogeneous catalysis with organic ligands remains challenging since the ligands are often bound to the most active sites on the catalysts' surfaces. In this work, gold nanoparticles, which are on average less than 2 nm in diameter, are synthesized with strongly binding thiol and phosphine ligands and have measurable quantities of accessible sites on their surfaces in both cases. Triphenylphosphine (TPP) is used as the phosphine ligand, while triphenylmethyl mercaptan (TPMT) serves as the thiol ligand. Phosphines are chosen because they are electron-donating ligands when bound to Au, and thiols are selected because they are electron-withdrawing on the Au surface. X-ray photoelectron spectroscopy (XPS) results show differences in the Au 4f binding energies between the TPP- and TPMT-bound Au nanoparticles. Fourier transform infrared spectroscopy (FTIR) measurements of bound CO indicate that the TPP-bound Au nanoparticles are more electron-rich than the TPMT-bound Au nanoparticles. The number of binding sites on the surface is quantified using 2-naphthalenethiol titration experiments. It is observed that the number of binding sites on the thiol and phosphine-bound Au nanoparticles is similar in both cases. The Au nanoparticles are used for three different reactions: resazurin reduction, CO oxidation, and benzyl alcohol oxidation. For both CO oxidation and benzyl alcohol oxidation, which are performed with the ligands attached, TPP- and TPMT-bound nanoparticles are both catalytically active. However, for resazurin reduction, the TPMT-bound Au nanoparticles are not active, while the TPP-bound Au nanoparticles are catalytically active. These results illustrate that the catalytic activity can be tuned using bound organic ligands with different electronic properties for reduction reactions using Au nanoparticle catalysts.

Enhanced Catalytic Activity of TEMPO-Mediated Aerobic Oxidation of Alcohols via Redox-Active Metal-Organic Framework Nodes

Metal-organic frameworks (MOFs) are outstanding platforms for heterogeneous catalysis due to their tunable pore size, huge surface area, large porosity, and potential active sites. The design and synthesis of MOF/organocatalyst co-catalytic systems have attracted considerable interest owing to their high catalytic activity, low toxicity, and mild reaction conditions. Herein, we reported the synthesis of a bifunctional TEMPO-IsoNTA organocatalyst featuring a pyridyl group as an anchoring site and a TEMPO radical as a catalytic active site. By using the topologically isomorphic structures of MIL-101(Fe) and MIL-101(Cr) as co-catalysts, these MOF/TEMPO-IsoNTA systems enable the efficient aerobic oxidation of various alcohols to their corresponding aldehydes or ketones under mild conditions. Notably, the MIL-101(Fe)/TEMPO-IsoNTA system exhibits superior catalytic activity, thanks to their redox-active Fe^III-oxo nodes, which facilitate the regeneration of TEMPO-IsoNTA. Our research not only solves the problem of potential heavy metal contamination in the TEMPO-based homogeneous catalytic system, but also enriches the understanding of synergism of MOFs/organocatalysts.

Nanoarchitectonics and Catalytic Performance of Au-Pd Nanoflowers Supported on Fe2O3

Supported anisotropic bimetallic nanocrystals are attractive owing to their potential for novel catalytic applications. Au-Pd nanocrystals are expected to have higher catalytic activity for alcohol oxidation than Au nanocrystals. However, only a few studies have reported the application of anisotropic Au-Pd nanocrystals as alcohol-oxidation nanocatalysts. Support materials such as Al2O3 and Fe2O3 influence the catalytic activity of spherical Au nanoparticles. Thus, optimization of the support is expected to improve the catalytic activity of anisotropic Au-Pd nanocrystals. Herein, we report the synthesis and catalytic performances of Al2O3- and Fe2O3-supported Au and Au-Pd nanoflowers. Au99-Pd1 NFs supported on Fe2O3 exhibited the highest catalytic activity for 1-phenylethyl alcohol oxidation.

Selective Oxidation of Alcohols through Fe3 O4 @SiO2 /K2 CO3 -Glycerin Deep Eutectic Solvent as a Heterogeneous Catalytic System

K₂ CO₃ /Glycerin as a deep eutectic solvent (DES) was anchored covalently onto functionalized magnetic nanoparticles and showed a significant activity towards the oxidation of various alcohols under mild conditions with a short reaction time and good to high yield. A combination of the magnetic nanoparticles and deep eutectic solvent offers a novel, green, reusable catalyst with easy separation. Also, the catalyst structure was well characterized using techniques such as FT-IR spectroscopy, XRD, SEM, TGA, BET, VSM, TEM, and energy-dispersive X-ray spectroscopy (EDS).

High-Entropy Intermetallic PtRhBiSnSb Nanoplates for Highly Efficient Alcohol Oxidation Electrocatalysis

The control of multimetallic ensembles at the atomic-level is challenging, especially for high-entropy alloys (HEAs) possessing five or more elements. Herein, the one-pot synthesis of hexagonal-close-packed (hcp) PtRhBiSnSb high-entropy intermetallic (HEI) nanoplates with intrinsically isolated Pt, Rh, Bi, Sn, and Sb atoms is reported, to boost the electrochemical oxidation of liquid fuels. Taking advantage of these combined five metals, the well-defined PtRhBiSnSb HEI nanoplates exhibit a remarkable mass activity of 19.529, 15.558, and 7.535 A mg^-1 _Pt+Rh toward the electrooxidation of methanol, ethanol, and glycerol in alkaline electrolytes, respectively, representing a state-of-the-art multifunctional electrocatalyst for alcohol oxidation reactions. In particular, the PtRhBiSnSb HEI achieves record-high methanol oxidation reaction (MOR) activity in an alkaline environment. Theoretical calculations demonstrate that the introduction of the fifth metal Rh enhances the electron-transfer efficiency in PtRhBiSnSb HEI nanoplates, which contributes to the improved oxidation capability. Meanwhile, robust electronic structures of the active sites are achieved due to the synergistic protections from Bi, Sn, and Sb sites. This work offers significant research advances in developing well-defined HEA with delicate control over compositions and properties.

Metal-Free Boron/Phosphorus Co-Doped Nanoporous Carbon for Highly Efficient Benzyl Alcohol Oxidation

An in-depth understanding of the electronic structures of catalytically active centers and their surrounding vicinity is key to clarifying the structure-activity relationship, and thus enabling the design and development of novel metal-free carbon-based materials with desired catalytic performance. In this study, boron atoms are introduced into phosphorus-doped nanoporous carbon via an efficient strategy, so that the resulting material delivers better catalytic performance. The doped B atoms alter the electronic structures of active sites and cause the adjacent C atoms to act as additional active sites that catalyze the reaction. The B/P co-doped nanoporous carbon shows remarkable catalytic performance for benzyl alcohol oxidation, achieving high yield (over 91% within 2 h) and selectivity (95%), as well as low activation energy (32.2 kJ mol^-1 ). Moreover, both the conversion and selectivity remain above 90% after five reaction cycles. Density functional theory calculations indicate that the introduction of B to P-doped nanoporous carbon significantly increases the electron density at the Fermi level and that the oxidation of benzyl alcohol occurs via a different reaction pathway with a very low energy barrier. These findings provide important insights into the relationship between catalytic performance and electronic structure for the design of dual-doped metal-free carbon catalysts.

Photochemical Hydrogen Storage with Hexaazatrinaphthylene (HATN)

When irradiated with violet light, hexaazatrinaphthylene (HATN) extracts a hydrogen atom from an alcohol forming a long-living hydrogenated species. The kinetic isotope effect for fluorescence decay in deuterated methanol (1.56) indicates that the lowest singlet excited state of the molecule is a precursor for intermolecular hydrogen transfer. The photochemical hydrogenation occurs in several alcohols (methanol, ethanol, isopropanol) but not in water. Hydrogenated HATN can be detected optically by an absorption band at 1.78 eV as well as with EPR and NMR techniques. Mass spectroscopy of photoproducts reveal di-hydrogenated HATN structures along with methoxylated and methylated HATN molecules which are generated through the reaction with methoxy radicals (remnants from alcohol splitting). Experimental findings are consistent with the theoretical results which predicted that for the excited state of the HATN-solvent molecular complex, there exists a barrierless hydrogen transfer from methanol but a barrier for the similar oxidation of water.

Mechanistic Insights into Selective Acetaldehyde Formation from Ethanol Oxidation on Hematite Photoanodes by Operando Spectroelectrochemistry

This study employed operando spectroelectrochemical l and photoelectrochemical methods to investigate the charge carrier dynamics of photogenerated holes in hematite for ethanol oxidation and its possible over-oxidation. Ethanol oxidation was found to form acetaldehyde with around 100 % initial selectivity and faradaic efficiency. The overoxidation of acetaldehyde was suppressed by being unable to kinetically compete with ethanol oxidation in terms of turnover frequency by a factor of ten. Temperature-dependent rate law analyses were applied to determine the activation energies of these two oxidations. For the ethanol oxidation, the activation energy was 195 meV, compared to 398 meV for acetaldehyde oxidation. These results were correlated with the valence band potential to elucidate the advantage of using hematite for safer and sustainable value-added aldehyde synthesis compared to the industrial method. The dynamics of ethanol oxidation also addressed the challenges in broad-spectrum deep oxidation of organic compounds in water purification using metal oxides.

Oxidase enzymes as sustainable oxidation catalysts

Oxidation is one of the most important processes used by the chemical industry. However, many of the methods that are used pose significant sustainability and environmental issues. Biocatalytic oxidation offers an alternative to these methods, with a now significant enzymatic oxidation toolbox on offer to chemists. Oxidases are one of these options, and as they only depend on molecular oxygen as a terminal oxidant offer perfect atom economy alongside the selectivity benefits afforded by enzymes. This review will focus on examples of oxidase biocatalysts that have been used for the sustainable production of important molecules and highlight some important processes that have been significantly improved through the use of oxidases. It will also consider emerging classes of oxidases, and how they might fit in a future biorefinery approach for the sustainable production of important chemicals.

A Perspective on Heterogeneous Catalysts for the Selective Oxidation of Alcohols

Selective oxidation of higher alcohols using heterogeneous catalysts is an important reaction in the synthesis of fine chemicals with added value. Though the process for primary alcohol oxidation is industrially established, there is still a lack of fundamental understanding considering the complexity of the catalysts and their dynamics under reaction conditions, especially when higher alcohols and liquid‐phase reaction media are involved. Additionally, new materials should be developed offering higher activity, selectivity, and stability. This can be achieved by unraveling the structure–performance correlations of these catalysts under reaction conditions. In this regard, researchers are encouraged to develop more advanced characterization techniques to address the complex interplay between the solid surface, the dissolved reactants, and the solvent. In this mini‐review, we report some of the most important approaches taken in the field and give a perspective on how to tackle the complex challenges for different approaches in alcohol oxidation while providing insight into the remaining challenges.

A Copper(I) Complex with Two Unpaired Electrons, Synthesised by Oxidation of a Copper(II) Complex with Two Redox-Active Ligands

Two homoleptic copper(II) complexes [Cu(L1)2 ] and [Cu(L2)2 ] with anionic redox-active ligands were synthesised, one with urea azine (L1) and the other with thio-urea azine (L2) ligands. One-electron oxidation of the complexes initiates an unprecedented redox-induced electron transfer process, leading to monocationic copper(I) complexes [Cu(L1)2 ]+ and [Cu(L2)2 ]+ with two oxidised ligands. While [Cu(L1)2 ]+ is best described as a CuI complex with two neutral radical ligands that couple antiferromagnetically, [Cu(L2)2 ]+ is a CuI complex with two clearly different ligand units in the solid state and with a magnetic susceptibility close to a diamagnetic compound. Further one-electron oxidation of the complex with L1 ligands results in a dication [Cu(L1)2 ]2+ , best described as a CuI complex with a twofold oxidised, monocationic ligand and a neutral radical ligand. The stability in at least three redox states, the accumulation of spin density at the ligands and the facile ligand-metal electron transfer make these complexes highly attractive for a variety of applications; here the catalytic aerobic oxidation of alcohols to aldehydes is tested.

Nano-Sized NiO Immobilized on Au/CNT for Benzyl Alcohol Oxidation: Influences of Hybrid Structure and Interface

Tiny gold nanoparticles were successfully anchored on carbon nanotubes (CNT) with NiO decoration by a two-step synthesis. Characterizations suggested that Ni species in an oxidative state preferred to be highly dispersed on CNT. During the synthesis, in situ reduction by NaBH₄ and thermal treatment in oxidation atmosphere were consequently carried out, causing the formation of Au-Ni-O_x interfaces and bimetal hybrid structure depending on the Ni/Au atomic ratios. With an appropriate Ni/Au atomic ratio of 8:1, Ni atoms migrated into the sub-layers of Au particles and induced the lattice contraction of Au particles, whilst a higher Ni/Au atomic ratio led to the accumulation of NiO fractions surrounding Au particles. Both contributed to the well-defined Au-Ni-O_x interface and accelerated reaction rates. Nickel species acted as structure promoters with essential Au-Ni-O_x hybrid structure as well as the active oxygen supplier, accounting for the enhanced activity for benzyl alcohol oxidation. However, the over-layer of unsaturated gold sites easily occured under a high Ni/Au ratio, resulting in a lower reaction rate. With an Au/Ni atomic ratio of 8:1, the specific rate of AuNi₈/CNT reached 185 μmol/g/s at only 50 °C in O₂ at ordinary pressure.

Spectroscopic Characterization of a Reactive [Cu2 (μ-OH)2 ]2+ Intermediate in Cu/TEMPO Catalyzed Aerobic Alcohol Oxidation Reaction

Cu^I/TEMPO (TEMPO=2,2,6,6‐tetramethylpiperidinyloxyl) catalyst systems are versatile catalysts for aerobic alcohol oxidation reactions to selectively yield aldehydes. However, several aspects of the mechanism are yet unresolved, mainly because of the lack of identification of any reactive intermediates. Herein, we report the synthesis and characterization of a dinuclear [L1₂Cu₂]²⁺ complex 1, which in presence of TEMPO can couple the catalytic 4 H⁺/4 e⁻ reduction of O₂ to water to the oxidation of benzylic and aliphatic alcohols. The mechanisms of the O₂‐reduction and alcohol oxidation reactions have been clarified by the spectroscopic detection of the reactive intermediates in the gas and condensed phases, as well as by kinetic studies on each step in the catalytic cycles. Bis(μ‐oxo)dicopper(III) (2) and bis(μ‐hydroxo)dicopper(II) species 3 are shown as viable reactants in oxidation catalysis. The present study provides deep mechanistic insight into the aerobic oxidation of alcohols that should serve as a valuable foundation for ongoing efforts dedicated towards the understanding of transition‐metal catalysts involving redox‐active organic cocatalysts.

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

With 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.

Photoredox-Catalyzed Simultaneous Olefin Hydrogenation and Alcohol Oxidation over Crystalline Porous Polymeric Carbon Nitride

Booming of photocatalytic water splitting technology (PWST) opens a new avenue for the sustainable synthesis of high-value-added hydrogenated and oxidized fine chemicals, in which the design of efficient semiconductors for the in-situ and synergistic utilization of photogenerated redox centers are key roles. Herein, a porous polymeric carbon nitride (PPCN) with a crystalline backbone was constructed for visible light-induced photocatalytic hydrogen generation by photoexcited electrons, followed by in-situ utilization for olefin hydrogenation. Simultaneously, various alcohols were selectively transformed to valuable aldehydes or ketones by photoexcited holes. The porosity of PPCN provided it with a large surface area and a short transfer path for photogenerated carriers from the bulk to the surface, and the crystalline structure facilitated photogenerated charge transfer and separation, thus enhancing the overall photocatalytic performance. High reactivity and selectivity, good functionality tolerance, and broad reaction scope were achieved by this concerted photocatalysis system. The results contribute to the development of highly efficient semiconductor photocatalysts and synergistic redox reaction systems based on PWST for high-value-added fine chemical production.

On-Surface Alcohol Oxidation Monitored by Paper Spray Mass Spectrometry: The Role of Ruthenium as Catalyst

Paper spray ionization mass spectrometry (PS-MS) is employed herein as a convenient platform to investigate an on-surface catalytic process, that is, the oxidation of alcohols induced by ruthenium salts. The tag-charged benzyl alcohol 1 (m/z 166), used as a suitable prototype starting substrate, is quickly oxidized by tert-butyl hydroperoxide (TBHP) in an on-surface process catalyzed by ruthenium trichloride (RuCl₃). The PS(+)-MS revealed the formation of products from the oxidation of alcohol 1. RuCl₃ and TBHP played a crucial role in this process since when salts of other metals (platinum, palladium, and iron) and another oxidizing agent (hydrogen peroxide) are employed, no reaction is observed. Moreover, UV radiation and heating accelerate the on-surface alcohol 1 oxidation. Finally, an exciting possibility is to employ PS-MS to investigate similar organic catalytic reactions to accelerate them and detect unstable intermediates, indiscernible in the condensed phase.

Molecular Triad Containing a TEMPO Catalyst Grafted on Mesoporous Indium Tin Oxide as a Photoelectrocatalytic Anode for Visible Light-Driven Alcohol Oxidation

Photoelectrochemical cells based on semiconductors are among the most studied methods of artificial photosynthesis. This study concerns the immobilization, on a mesoporous conducting indium tin oxide electrode (nano-ITO), of a molecular triad (NDADI-P-Ru-TEMPO) composed of a ruthenium tris-bipyridine complex (Ru) as photosensitizer, connected at one end to 2,2,6,6-tetramethyl-1-piperidine N-oxyl (TEMPO) as alcohol oxidation catalyst and at the other end to the electron acceptor naphthalenedicarboxyanhydride dicarboximide (NDADI). Light irradiation of NDADI-P-Ru-TEMPO grafted to nano-ITO in a pH 10 carbonate buffer effects selective oxidation of para-methoxybenzyl alcohol (MeO-BA) to para-methoxybenzaldehyde with a TON of approximately 150 after 1 h of photolysis at a bias of 0.4 V vs. SCE. The faradaic efficiency is found to be of 80±5 %. The photophysical study indicates that photoinduced electron transfer from the Ru complex to NDADI is a slow process and must compete with direct electron injection into ITO to have a better performing system. This work sheds light on some of the important ways to design more efficient molecular systems for the preparation of photoelectrocatalytic cells based on catalyst-dye-acceptor arrays immobilized on conducting electrodes.

Oxidation of Benzyl Alcohol Using Cobalt Oxide Supported Inside and Outside Hollow Carbon Spheres

Cobalt oxide nanoparticles (6 nm) supported both inside and outside of hollow carbon spheres (HCSs) were synthesized by using two different polymer templates. The oxidation of benzyl alcohol was used as a model reaction to evaluate the catalysts. PXRD studies indicated that the Co oxidation state varied for the different catalysts due to reduction of the Co by the carbon, and a metal oxidation step prior to the benzyl alcohol oxidation enhanced the catalytic activity. The metal loading influenced the catalytic efficiency, and the activity decreased with increasing metal loading, possibly due to pore filling effects. The catalysts showed similar activity and selectivity (to benzaldehyde) whether placed inside or outside the HCS (63 % selectivity at 50 % conversion). No poisoning was observed due to product build up in the HCS.

Pyrroloquinoline Quinone Aza-Crown Ether Complexes as Biomimetics for Lanthanide and Calcium Dependent Alcohol Dehydrogenases*

Understanding the role of metal ions in biology can lead to the development of new catalysts for several industrially important transformations. Lanthanides are the most recent group of metal ions that have been shown to be important in biology, that is, in quinone‐dependent methanol dehydrogenases (MDH). Here we evaluate a literature‐known pyrroloquinoline quinone (PQQ) and 1‐aza‐15‐crown‐5 based ligand platform as scaffold for Ca²⁺, Ba²⁺, La³⁺ and Lu³⁺ biomimetics of MDH and we evaluate the importance of ligand design, charge, size, counterions and base for the alcohol oxidation reaction using NMR spectroscopy. In addition, we report a new straightforward synthetic route (3 steps instead of 11 and 33 % instead of 0.6 % yield) for biomimetic ligands based on PQQ. We show that when studying biomimetics for MDH, larger metal ions and those with lower charge in this case promote the dehydrogenation reaction more effectively and that this is likely an effect of the ligand design which must be considered when studying biomimetics. To gain more information on the structures and impact of counterions of the complexes, we performed collision induced dissociation (CID) experiments and observe that the nitrates are more tightly bound than the triflates. To resolve the structure of the complexes in the gas phase we combined DFT‐calculations and ion mobility measurements (IMS). Furthermore, we characterized the obtained complexes and reaction mixtures using Electron Paramagnetic Resonance (EPR) spectroscopy and show the presence of a small amount of quinone‐based radical.

Bimetallic PdAu Catalysts within Hierarchically Porous Architectures for Aerobic Oxidation of Benzyl Alcohol

Hierarchically porous (HP) zeotype materials (possessing both micropores and mesopores) offer improved diffusional access to intra-framework active sites, analogous to mesoporous materials, yet retain the high selectivity of the microporous (MP) bulk. We have recently designed crystalline hierarchically porous silicoaluminophosphates (SAPOs) with enhanced mass-transport characteristics, which can lead to significant improvement in catalytic activity and catalyst lifetime. In this study, we have prepared PdAu bimetallic nanostructures supported on HP-SAPO frameworks by an incipient impregnation of metal precursors followed by H₂ reduction at 300 °C, for the aerobic oxidation of benzyl alcohol to benzaldehyde. PdAu NPs supported on HP framework displayed significantly enhanced catalytic activities, when compared with their MP analogues, clearly highlighting the benefits of introducing hierarchical porosity in the SAPO support matrix.

Catalytic Performance of a Magnetic Core-Shell Iron(II) C-Scorpionate under Unconventional Oxidation Conditions

For the first time, herein is reported the use of a magnetic core-shell support for a C-scorpionate metallic complex. The prepared hybrid material, that consists on the C-scorpionate iron(II) complex [FeCl₂{κ³-HC(pz)₃}] (pz, pyrazolyl) immobilized at magnetic core-shell particles (Fe₃O₄/TiO₂), was tested as catalyst for the oxidation of secondary alcohols using the model substrate 1-phenylethanol. Moreover, the application of alternative energy sources (e.g., ultrasounds, microwaves, mechanical or thermal) for the peroxidative alcohol oxidation using the magnetic heterogenized iron(II) scorpionate led to different/unusual outcomes that are presented and discussed.

Fabrication of Fe3O4@PVA-Cu Nanocomposite and Its Application for Facile and Selective Oxidation of Alcohols

Fe₃O₄@PVA-Cu nanocomposite was introduced as an affordable catalyst for selective oxidation of alcohols into various aldehydes and ketones. The synthesized nanocomposite was characterized by applying essential analyses. The peaks that are appeared in FT-IR spectroscopy confirmed the production of the Fe₃O₄@PVA-Cu nanocomposite. In addition, EDX analysis proved the presence of oxygen, carbon, iron, and copper elements in the catalyst. Further, TGA analysis showed high thermal stability of the nanocomposite. VSM technique was applied to examine the magnetic property of the nanocomposite. The results demonstrated a high magnetic property in the catalyst, which enables easy separation of it from the reaction solution. TEM and SEM imaging showed the nanoscale size of the particles (~20 nm) in the catalyst. Additionally, XRD data was compatible with that of Fe₃O₄ nanoparticles. The application of the nanocomposite has been studied in the selective oxidation of alcohols in the presence of acetonitrile as solvent, and hydrogen peroxide as a supplementary oxidizing agent. This technique is remarkably facile and inexpensive. Further, the products showed high yields. In addition, the calculated TON and TOF values indicated the phenomenal efficiency of the nanocomposite in preparation of targeted products.

A Woven Supramolecular Metal-Organic Framework Comprising a Ruthenium Bis(terpyridine) Complex and Cucurbit[8]uril: Enhanced Catalytic Activity toward Alcohol Oxidation

The self-assembly of a diamondoid woven supramolecular metal-organic framework wSMOF-1 has been achieved from intertwined [Ru(tpy)₂ ]²⁺ (tpy=2,2',6',2''-terpyridine) complex M1 and cucurbit[8]uril (CB[8]) in water, where the intermolecular dimers formed by the appended aromatic arms of M1 are encapsulated in CB[8]. wSMOF-1 exhibits ordered pore periodicity in both water and the solid state, as confirmed by a combination of ¹ H NMR spectroscopy, UV-vis absorption, isothermal titration calorimetry, dynamic light scattering, small angle X-ray scattering and selected area electron diffraction experiments. The woven framework has a pore aperture of 2.1 nm, which allows for the free access of both secondary and primary alcohols and tert-butyl hydroperoxide (TBHP). Compared with the control molecule [Ru(tpy)₂ ]Cl₂ , the [Ru(tpy)₂ ]²⁺ unit of wSMOF-1 exhibits a remarkably higher heterogeneous catalysis activity for the oxidation of alcohols by TBHP in n-hexane. For the oxidation of 1-phenylethan-1-ol, the yield of acetophenone was increased from 10 % to 95 %.

Solar-Driven Carbon Nanoreactor Coupling Gold and Platinum Nanocatalysts for Alcohol Oxidations

This research reports gold (Au) and platinum (Pt) nanocatalysts spatially confined in a porous carbon nanosphere as a new solar-driven carbon nanoreactor (CNR). The CNRs have confined size (≈100 nm), high specific surface area, and high thermal and electrical conductivity. The black color of CNR can improve the energy harvest efficiency of the solar irradiation to thermal energy within each nanoreactor. The localized surface plasmon resonance (LSPR) on Au nanocatalysts-induced electron oscillation causes the localized heating effect inside each CNR. Therefore, the heat will be accumulated in the confined space of CNR and transferred to reaction energy to drive the alcohol oxidation on uniformly dispersed Au and Pt nanoparticles inside the nanoreactor. The energetic electrons induced by LSPR effect on the surface of Au nanoparticles are transferred to the nearby and more active Pt surface via the conductive CNR, which strongly enhances the conversion of cinnamyl alcohol from 14% on Pt-CNR up to 100% on AuPt-CNR after a 3 h reaction. Therefore, the cooperative effect of Au and Pt nanoparticles confined in the CNRs utilized in this work can largely increase the efficiency of harvesting solar energy to drive the important chemical processes.

Aroylhydrazone Schiff Base Derived Cu(II) and V(V) Complexes: Efficient Catalysts towards Neat Microwave-Assisted Oxidation of Alcohols

A new hexa-nuclear Cu(II) complex [Cu₃(μ₂-1κNO²,2κNO²-L)(μ-Cl)₂(Cl)(MeOH)(DMF)₂]₂ (1), where H₄L = N′¹,N′²-bis(2-hydroxybenzylidene)oxalohydrazide, was synthesized and fully characterized by IR spectroscopy, ESI-MS, elemental analysis, and single crystal X-ray diffraction. Complex 1 and the dinuclear oxidovanadium(V) one [{VO(OEt)(EtOH)}₂(1κNO²,2κNO²-L)]·2H₂O (2) were used as catalyst precursors for the neat oxidation of primary (cinnamyl alcohol) and secondary (1-phenyl ethanol, benzhydrol) benzyl alcohols and of the secondary aliphatic alcohol cyclohexanol, under microwave irradiation using tert-butyl hydroperoxide (TBHP) as oxidant. Oxidations proceed via radical mechanisms. The copper(II) compound 1 exhibited higher catalytic activity than the vanadium(V) complex 2 for all the tested alcohol substrates. The highest conversion was found for 1-phenylethanol, yielding 95.3% of acetophenone in the presence of 1 and in solvent and promoter-free conditions. This new Cu(II) complex was found to exhibit higher activity under milder reaction conditions than the reported aroylhydrazone Cu(II) analogues.

Aerobic Oxidation of Alcohols Catalyzed by in Situ Generated Gold Nanoparticles inside the Channels of Periodic Mesoporous Organosilica with Ionic Liquid Framework

In situ generated gold nanoparticles inside the nanospaces of periodic mesoporous organosilica with an imidazolium framework (Au@PMO-IL) were found to be highly active, selective, and reusable catalysts for the aerobic oxidation of activated and nonactivated alcohols under mild reaction conditions. The catalyst was characterized by nitrogen adsorption-desorption measurement, thermogravimetric analysis (TGA), transmission electron microscopy (TEM), elemental analysis (EA), diffuse reflectance infrared Fourier transform spectroscopy (DRIFT), X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma atomic emission spectroscopy (ICP-AES). The catalyst exhibited excellent catalytic activity in the presence of either Cs₂CO₃ (35 °C) or K₂CO₃ (60 °C) as reaction bases in toluene as a reaction solvent. Under both reaction conditions, various types of alcohols (up to 35 examples) including activated benzylic, primary and secondary aliphatic, heterocyclic, and challenging cyclic aliphatic alcohols converted to the expected carbonyl compounds in good to excellent yields and selectivity. The catalyst was also recovered and reused for at least seven reaction cycles. Data from three independent leaching tests indicated that amounts of leached gold particles were negligible (<0.2 ppm). It is believed that the combination of bridged imidazolium groups and confined nanospaces of PMO-IL might be a major reason explaining the remarkable stabilization and homogeneous distribution of in situ generated gold nanoparticles, thus resulting in the highly active and recyclable catalyst system.

Ultrasound and Radiation-Induced Catalytic Oxidation of 1-Phenylethanol to Acetophenone with Iron-Containing Particulate Catalysts

Iron-containing particulate catalysts of 0.1–1 µm size were prepared by wet and ball-milling procedures from common salts and characterized by FTIR, TGA, UV-Vis, PXRD, FEG-SEM, and XPS analyses. It was found that when the wet method was used, semi-spherical magnetic nanoparticles were formed, whereas the mechanochemical method resulted in the formation of nonmagnetic microscale needles and rectangles. Catalytic activity of the prepared materials in the oxidation of 1-phenylethanol to acetophenone was assessed under conventional heating, microwave (MW) irradiation, ultrasound (US), and oscillating magnetic field of high frequency (induction heating). In general, the catalysts obtained by wet methods exhibit lower activities, whereas the materials prepared by ball milling afford better acetophenone yields (up to 83%). A significant increase in yield (up to 4 times) was observed under the induction heating if compared to conventional heating. The study demonstrated that MW, US irradiations, and induction heating may have great potential as alternative ways to activate the catalytic system for alcohol oxidation. The possibility of the synthesized material to be magnetically recoverable has been also verified.

Supported Gold Nanoparticles as Catalysts in Peroxidative and Aerobic Oxidation of 1-Phenylethanol under Mild Conditions

The efficiency of Au/TiO₂ based catalysts in 1-phenylethanol oxidation was investigated. The role of support modifiers (La₂O₃ or CeO₂), influence of gold loading (0.5% or 4%) and redox pretreatment atmosphere, catalyst recyclability, effect of oxidant: tert-butyl hydroperoxide (TBHP) or O₂, as well as the optimization of experimental parameters of the reaction conditions in the oxidation of this alcohol were studied and compared with previous studies on 1-octanol oxidation. Samples were characterized by temperature-programmed oxygen desorption (O₂-TPD) method. X-ray photoelectron spectroscopy (XPS) measurements were carried out for used catalysts to find out the reason for deactivation in 1-phenylethanol oxidation. The best catalytic characteristics were shown by catalysts modified with La₂O₃, regardless of the alcohol and the type of oxidant. When O₂ was used, the catalysts with 0.5% Au, after oxidative pretreatment, showed the highest activity in both reactions. The most active catalysts in 1-phenylethanol oxidation with TBHP were those with 4% Au and the H₂ treatment, while under the same reaction conditions, 0.5% Au and O₂ treatment were beneficial in 1-octanol oxidation. Despite the different chemical nature of the substrates, it seems likely that Au⁺(Au^δ+) act as the active sites in both oxidative reactions. Density functional theory (DFT) simulations confirmed that the gold cationic sites play an essential role in 1-phenylethanol adsorption.

Acceptorless Alcohol Dehydrogenation Catalysed by Pd/C

Although the selective oxidation of alcohols to carbonyl compounds is a critical reaction, it is often plagued by several challenges related to sustainability. Here, the continuous, acceptorless dehydrogenation of alcohols to carbonyl compounds over heterogeneous catalysts was demonstrated, in the absence of oxidants, bases or acceptor molecules. In addition to improving selectivity and atom efficiency, the absence of an acceptor resulted in the co-production of molecular H₂ , a clean energy source, and permitted dehydrogenation to proceed at >98 % selectivity at turnover frequency values amongst the highest in the literature. Moreover, excellent durability was observed during continuous operation over 48 h, reaching space-time yields of 0.683 g_(product)  mL^-1  h^-1 , better than the state of the art by over two orders of magnitude. Alongside these breakthroughs, the basic kinetic parameters of the reaction were also determined, allowing some of the elementary reaction steps to be identified.

Electrocatalytic Oxidation of Ethanol on the Surface of Graphene Based Nanocomposites: An Introduction and Review to it in Recent Studies

This review gives an overview of the electrochemical investigations about the properties of various types of graphene composites in the ethanol oxidation. Various routes to provide appropriate graphene-based materials required electrochemical techniques for investigation of different types of the materials as well as their performance and efficacy in ethanol oxidation are discussed in detail. Furthermore, it is demonstrated that the incorporation of suitable materials, e. g. noble metals (graphene-supported binary and ternary metal nanoparticles), metal oxides, conductive polymer, etc, with graphene results in excellent electrocatalytic activity, superb durability and selectivity in ethanol oxidation. Immobilization of electrocatalytically active NPs on graphene supports using physical approaches is considered as an effective route to prepare direct ethanol fuel cell (DEFC) anode catalysts.

Oxygen-Depleted Calixarenes as Ligands for Molecular Models of Galactose Oxidase

A calix[4]arene ligand, in which two of the phenol functions are replaced by pyrazole units has been employed to mimic the His₂ -Tyr₂ (His: histidine, Tyr: tyrosine) ligand sphere within the active site of the galactose oxidase (GO). The calixarene backbone forces the corresponding copper(II) complex into a see-saw-type structure, which is hitherto unprecedented in GO modelling chemistry. It undergoes a one-electron oxidation that is centered at the phenolate donor leading to a copper-coordinated phenoxyl radical like in the GO. Accordingly, the complex was tested as a functional model and indeed proved capable of oxidizing benzyl alcohol to the respective aldehyde using two phenoxyl-radical equivalents as oxidants. Finally, the results show that the calixarene platform can be utilized to arrange donor functions to biomimetic binding pockets that allow for the creation of novel types of model compounds.

Enhanced Photocatalytic Activity of Aerogel Composed of Crooked Carbon Nitride Nanolayers with Nitrogen Vacancies

Self-supported aerogel composed of carbon nitride nanolayers can act as a bifunctional photocatalyst and show enhanced photoreduction and photooxidation performance due to the large surface areas and nitrogen vacancies. The carbon nitride aerogel can catalyze hydrogen evolution at a rate of nearly 4.2 mmol h^-1 g^-1 and oxidize benzyl alcohols with a high conversion efficiency and selectivity under milder conditions. Note that the activity of carbon nitride aerogel for photochemical alcohol oxidation shows outstanding performance compared with carbon nitride based photocatalysts. Both density functional theory and experimental results demonstrate that the introduction of nitrogen vacancies within the carbon nitride aerogel contributes to the formation of a crooked structure and enhanced adsorption of oxygen compared with a bulk sample.

A Study of Catalytic Oxidation of a Library of C₂ to C₄ Alcohols in the Presence of Nanogold

The classical stoichiometric oxidation of alcohols is an important tool in contemporary organic chemistry. However, it still requires huge modifications in order to comply with the principles of green chemistry. The use of toxic chemicals, hazardous organic solvents, and the large amounts of toxic wastes that result from the reactions are a few examples of the problems that must be solved. Nanogold alone or conjugated with palladium were supported on different carriers (SiO₂, C) and investigated in order to evaluate their catalytic potential for environmentally friendly alcohol oxidation under solvent-free and base-free conditions in the presence H₂O₂ as a clean oxidant. We tested different levels of Au loading (0.1⁻1.2% wt.) and different active catalytic site forms (monometallic Au or bimetallic Au⁻Pd sites). This provided new insights on how the structure of the Au-dispersions affected their catalytic performance. Importantly, the examination of the catalytic performance of the resulting catalysts was oriented toward a broad scope of alcohols, including those that are the most resistant to oxidation-the primary aliphatic alcohols. Surprisingly, the studies proved that Au/SiO₂ at a level of Au loading as low as 0.1% wt. appeared to be efficient and prospective catalytic system for the green oxidation of alcohol. Most importantly, the results revealed that 0.1% Au/SiO₂ might be the catalyst of choice with a wide scope of utility in the green oxidation of various structurally different alcohols as well as the non-activated aliphatic ones.

Low- and High-Index Faceted Pd Nanocrystals Embedded in Various Oxygen-Deficient WO x Nanostructures for Electrocatalytic Oxidation of Alcohol (EOA) and Carbon Monoxide (CO)

This work suggests a modest hydrothermal method applied for the synthesis of oxygen-deficient WO _x ( x = 2.75, 2.83, and 2.94) nanomaterials with various morphologies, such as bundled nanorods (NR), nanobelts (NB), and nanosheets (NS), by changing the inorganic additives, such as HCl, NaHSO₄, and HNO₃. In addition, WO _x-supported high- and low-index faceted Pd nanoparticles (Pd-WO_2.75 NB, Pd-WO_2.83 NR, and Pd-WO_2.94 NS) have been successfully synthesized by a facile sonochemical method to enhance the high electrocatalytic activity of electrocatalysts for alcohol electrooxidation, including ethanol, ethylene glycol, and glycerol. Among the three different electrocatalysts, the versatile high-index {520} faceted Pd nanoparticles on WO_2.75 NB (Pd-WO_2.75 NB) show better electrocatalytic performance compared to low-index {100} faceted Pd-WO_2.83 NR and Pd-WO_2.94 NS nanocomposites. This work has identified that the high-density low-coordinated surface atom of Pd strongly interacts with alcohol, which facilitates C-C bond cleavage and may prevent the CO poisoning of nanoparticles. Furthermore, the high concentration of oxygen-deficient nano composites provided additional benefit for the generation of OH species and boosted the electrocatalytic performance of alcohols as well.

Metal-Support Cooperative Effects in Au/VPO for the Aerobic Oxidation of Benzyl Alcohol to Benzyl Benzoate

This paper studies the cooperative effect of Au nanoparticles deposited on vanadyl pyrophosphate oxide (VPO) in the liquid phase oxidation of benzyl alcohol. VPO was prepared using the classical method by thermally treating VOHPO₄·0.5H₂O precursor in reacting atmosphere at 420 °C for a period of 72 h. Au nanoparticles were deposited by incipient wetness method. The catalysts were characterized by means of XRD, TEM, XPS and Raman. The bulk VPO catalyst contains vanadyl pyrophosphate phase ((VO)₂P₂O₇), and a small amount of VOPO₄. The catalytic system exhibits a high activity in the base-free liquid phase oxidation of alcohols compared to Au on activated carbon, classic catalyst used for this type of reaction. Au/VPO showed a high peculiar selectivity to benzyl benzoate (76%), an important product used in the pharmaceutical and perfume industries. This behavior might be ascribed to the presence of strong acid sites of VPO, as determined by liquid phase titration. Stability tests performed on Au/VPO showed a deactivation of 10% after the first run, but a constant conversion along the following five cycles. This phenomenon can be attributed to the increase of mean Au particle size (from 19.1 to 23.4 nm) after recycling tests as well as the partial leaching of Au and V in the reaction media. Moreover, XRD evidenced a modification in the VPO structure with the partial formation of VOHPO₄·0.5H₂O phase.

Au-Ag Nanoflower Catalysts with Clean Surfaces for Alcohol Oxidation

Shape-controlled metal nanocrystals, such as nanowires and nanoflowers, are attractive owing to their potentially novel catalytic properties and bimetallic nanocrystals composed of two distinct metals are expected to act as highly active catalysts. However, their catalytic activities are limited because of the capping agents adsorbed on the metal surfaces, which are necessary for the preparation and dispersion of these nanocrystals in solvents. Therefore, the preparation of bimetallic shape-controlled noble metal nanocrystals with clean surfaces, devoid of almost all capping agents, are expected to have high catalytic activity. Herein, we report the preparation of bimetallic Au-Ag nanoflowers using melamine as the capping agent. The bimetallic Au-Ag nanoflowers with a clean surface were subsequently obtained by a support and extraction method. The bimetallic nanoflowers with a clean surface were then used for the aerobic oxidation of 1-phenylethyl alcohol and they exhibited high rates for the formation of acetophenone compared to Au nanoflowers and spherical nanoparticles with almost the same size and Au/Ag ratio. We also show that Au-Ag nanoflowers containing only 1 % Ag (Au₉₉ -Ag₁ NFs) exhibit the highest rate of acetophenone formation among Au-Ag nanoflowers with different Au/Ag ratios owing to an increase in the electron density of the Au atoms that act as active sites for the oxidation of 1-phenylethyl alcohol.

Zr-Metal-Organic Frameworks Featuring TEMPO Radicals: Synergistic Effect between TEMPO and Hydrophilic Zr-Node Defects Boosting Aerobic Oxidation of Alcohols

Metal-organic frameworks (MOFs) featuring multiple catalytic units are excellent platforms for heterogeneous catalysis. However, the synergism between multiple catalytic units for catalysis is far from being well understood. Herein, we reported the synthesis of a robust 2,2,6,6-tetramethylpiperidinyloxy (TEMPO) radical-functionalized Zr-MOF (UiO-68-TEMPO) in the form of single-crystalline and microsized crystals with varied missing linker defects. Detailed catalytic studies and theoretical calculations reveal that the synergistic effect between the TEMPO radicals and hydrophilic and defective Zr-nodes endows UiO-68-TEMPO with superior catalytic activity toward aerobic oxidation of alcohols. Our work not only offers a new route to design and synthesize highly effective MOF catalysts but also provides insights into the synergism between multiple catalytic sites.

Enhancing cofactor recycling in the bioconversion of racemic alcohols to chiral amines with alcohol dehydrogenase and amine dehydrogenase by coupling cells and cell-free system

Alcohol dehydrogenase (ADH) and amine dehydrogenase (AmDH)-catalyzed one-pot cascade conversion of an alcohol to an amine provides a simple preparation of chiral amines. To enhance the cofactor recycling in this reaction, we report a new concept of coupling whole-cells with the cell-free system to enable separated intracellular and extracellular cofactor regeneration and recycling. This was demonstrated by the respective biotransformation of racemic 4-phenyl-2-butanol 1a and 1-phenyl-2-propanol 1b to (R)-4-phenylbutan-2-amine 3a and (R)-1-phenylpropan-2-amine 3b. Escherichia coli cells expressing S-enantioselective CpsADH, R-enantioselective PfODH, and NADH oxidase (NOX) was developed to oxidize racemic alcohols 1a-b to ketones 2a-b with full conversion via intracellular NAD⁺ recycling. AmDH and glucose dehydrogenase (GDH) were used to convert ketones 2a-b to amines (R)-3a-b with 89-94% conversion and 891-943 times recycling of NADH. Combining the cells and enzymes for the cascade transformation of racemic alcohols 1a-b gave 70% and 48% conversion to the amines (R)-3a and (R)-3b in 99% ee, with a total turnover number (TTN) of 350 and 240 for NADH recycling, respectively. Improved results were obtained by using the E. coli cells with immobilized AmDH and GDH: (R)-3a was produced in 99% ee with 71-84% conversion and a TTN of 1410-1260 for NADH recycling, the highest value so far for the ADH-AmDH-catalyzed cascade conversion of alcohols to amines. The concept might be generally applicable to this type of reactions.

Structure-Mediated Charge Separation in Boron Carbon Nitride for Enhanced Photocatalytic Oxidation of Alcohol

Boron carbon nitride (BCN) is a promising earth-abundant photocatalyst for solar energy conversion. However, the photocatalytic activities of BCN materials remain moderate because of the fast electron-hole recombination. Herein, an ordered BCN structure is fabricated by a facile one-step thermal treatment strategy. The ordered structure of BCN is directly evident from powder X-ray diffraction and high-resolution transmission electron microscopy. Importantly, it is found that the long-period ordered structure can intrinsically accelerate the separation and transfer kinetics of photogenerated charge carriers. Benefiting from these advantages, the ordered BCN structure exhibits remarkable performance for photoinduced selective oxidation of benzyl alcohol compared with the pristine BCN counterpart. This work highlights the important role of the crystal structure of light-harvesting materials in affecting electron-hole separation and at the same time points to the ample potential for improving the photocatalytic performance.

NH3⋅H2O: The Simplest Nitrogen-Containing Ligand for Selective Aerobic Alcohol Oxidation to Aldehydes or Nitriles in Neat Water

Aqueous ammonia (NH3⋅H2O) has been shown to serve as the simplest nitrogen-containing ligand to effectively promote copper-catalyzed selective alcohol oxidation under air in water. A series of alcohols with varying electronic and steric properties were selectively oxidized to aldehydes with up to 95 % yield. Notably, by increasing the amount of aqueous ammonia in neat water, the exclusive formation of aryl nitriles was also accomplished with good-to-excellent yields. Additionally, the catalytic system exhibits a high level of functional group tolerance with -OH, -NO2, esters, and heteroaryl groups all being amenable to the reaction conditions. This one-pot and green oxidation protocol provides an important synthetic route for the selective preparation of either aldehydes or nitriles from commercially available alcohols.

Two-Dimensional Metal-Organic Layers on Carbon Nanotubes to Overcome Conductivity Constraint in Electrocatalysis

Application of metal-organic frameworks (MOFs) in electrocatalysis is of great interest, but is limited by low electrical conductivities of most MOFs. To overcome this limitation, we constructed a two-dimensional version of MOF-metal-organic layer (MOL) on conductive multiwalled carbon nanotubes (CNTs) via facile solvothermal synthesis. The redox-active MOLs supported on the CNT efficiently catalyze the electrochemical oxidation of alcohols to aldehydes and ketones. Interestingly, this CNT/MOL assembly also endowed the selectivity for primary versus secondary alcohols via well-designed interfacial interactions. This work opens doors toward a variety of designer electrocatalysts built from functional MOFs.

Catalytic Promiscuity of Galactose Oxidase: A Mild Synthesis of Nitriles from Alcohols, Air, and Ammonia

We report an unprecedented catalytically promiscuous activity of the copper-dependent enzyme galactose oxidase. The enzyme catalyses the one-pot conversion of alcohols into the related nitriles under mild reaction conditions in ammonium buffer, consuming ammonia as the source of nitrogen and dioxygen (from air at atmospheric pressure) as the only oxidant. Thus, this green method does not require either cyanide salts, toxic metals, or undesired oxidants in stoichiometric amounts. The substrate scope of the reaction includes benzyl and cinnamyl alcohols as well as 4- and 3-pyridylmethanol, giving access to valuable chemical compounds. The oxidation proceeds through oxidation from alcohol to aldehyde, in situ imine formation, and final direct oxidation to nitrile.