Selective Oxidation Of Aromatic Alcohols Research Articles

Efficient utilization of photogenerated electrons and holes for photocatalytic redox reactions using visible light-driven Au/ZnIn2S4 hybrid.

In this study, a new photocatalytic reaction system for simultaneous selective oxidation of aromatic alcohols to corresponding aldehydes and reduction of protons to H2 has been developed. The results reveal that compared with pure ZnIn2S4, the ZnIn2S4 photocatalysts modified with noble metal gold (Au/ZnIn2S4) significantly promote the photocatalytic performance. Among them, the 0.5% Au/ZnIn2S4 nanosheets shows the highest photocatalytic activity for selective oxidation of benzyl alcohol to benzaldehyde and hydrogen production, and the yields of H2 and benzaldehyde are 326.68 and 352.04 μmol under visible light irradiation for 4 h, respectively. Those are about 4.4 and 3.6 times higher than those of pure ZnIn2S4 sample (74.0 μmol H2 and 98.04 μmol benzaldehyde), respectively. The utilization ratio of photogenerated electrons to holes can achieve 92.8%. Additionally, the control experiments demonstrate that the photogenerated electrons and holes play significant roles during the reaction process. It is hoped that the current work can offer an avenue to utilize the photogenerated carriers more efficiently and to develop other photocatalytic reaction systems, such as nitrogen fixation and reduction of carbon dioxide.

Pd Nanoparticles‐Polyethylenemine‐Lipase Bionanohybrids as Heterogeneous Catalysts for Selective Oxidation of Aromatic Alcohols

AbstractA new kind of bionanohybrids, synthesized by using 63 kDa‐lipase from Candida rugosa (CRL) in the presence of polyethyleneimine (PEI) by in situ formation of Pd (0) nanoparticles (PdNPs) in aqueous media at room temperature were obtained. Addition of Triton X‐100 as additive was also used. XRD confirmed the formation of crystalline Pd (0) as metal species. TEM analyses revealed PdNPs ranging from 6 to 8 nm, whereas using Triton X‐100 the size range of the nanoparticles was 9 to 24 nm (mainly being 13 nm). PdNPs of biohybrid created only with Triton X‐100 ranged from 8 to 21 nm. The different heterogeneous nanobiohybrids were applied as catalyst in the oxidation of benzyl alcohol under mild conditions. In all cases, they were selective to the synthesis of alcohol to benzaldehyde without traces of carboxylic acid. More than >99 % conversion was obtained in THF at 50 °C under air as oxidant. The addition of hydrogen peroxide improved the conversion initially but the reaction was stopped at around 50–68 % conversion after 24 h in the best of cases. These new nanocatalysts synthesized using PEI showed a very high recyclability, maintaining >95 % activity after 5 cycles of use. Also successful results were obtained in the oxidation of other aromatic primary and secondary alcohols. The new PEI‐nanobiohybrids conserved the enzymatic activity and showed excellent results in metallic‐enzymatic domino reaction.

Effective use of photogenerated electrons and holes in a system: Photocatalytic selective oxidation of aromatic alcohols to aldehydes and hydrogen production

Effective utilization of photogenerated electrons and holes in a system is always a research hotspot. Photocatalysis has been identified as a promising solution to tackle the current environmental and energy issues. However, photogenerated holes or electrons were wasted in the traditional photocatalytic process. In the paper, a dual-function photocatalytic reaction system was constructed using dispersed Ptx-modified 2D-3D Zn3In2S6 hierarchical structures (x = 1–4). In the system, aromatic alcohols were photocatalytically selectively oxidated into aldehydes and protons were reduced to hydrogen by photogenerated holes and electrons, respectively. In the reaction process, one aromatic alcohol is first dehydrogenated into aromatic aldehyde and two H+ via the corresponding carbon-centered radical by consuming of two holes, and then two H+ ions dehydrogenated from OH group and α CH of alcohol are evolved into H2 by depleting of two electrons. Atomically dispersed Ptx could offer the maximum atom efficiency and significantly promote visible light absorption and separation of photogenerated electron-hole pairs. The cooperative photoredox system exhibits remarkable photocatalytic activity for visible light-driven splitting of aromatic alcohols. Under visible light irradiation for 6 h, The H2 output over 2.14% Pt/Zn3In2S6 reaches up to 950 μmol, which is around 7.5, 5.3 and 3.8 times higher than that over Zn3In2S6, Pt-nanoparticle/Zn3In2S6 and MoS2/Zn3In2S6, respectively. The apparent quantum efficiency (AQE) of 2.14% Pt/Zn3In2S6 at 400 nm is about 4.6%. The utilization rate of photogenerated electrons to holes could be achieved 98.2%. Moreover, Pt/Zn3In2S6 hybrid shows high stability even when Zn3In2S6 was stored for 12 months. Compared with two half-reactions: the photocatalytic selective organics transformation under O2 atmosphere and the water splitting with sacrificial reagents, such designed dual-purpose photocatalytic reaction not only could effective use of photogenerated electrons and holes for organics transformation and hydrogen production simultaneously but also shows much higher photocatalytic activity than two half-reactions. At the same time, the work also expands the research field of photocatalysis, such as N2 fixation and CO2 reduction by using of the as-produced H+.

Ultra-low content of Pt modified CdS nanorods: Preparation, characterization, and application for photocatalytic selective oxidation of aromatic alcohols and reduction of nitroarenes in one reaction system.

A series of Pt nanoparticles (with size of 3-4 nm) decorated CdS nanorods were prepared via a simple solvothermal method. The samples were then used for photocatalytic selective oxidation (SO) of aromatic alcohols and reduction (SR) of nitroarenes in one reaction system. The platinized samples showed enhanced activity for the conversions than pristine CdS as Pt can serve as e- trapping and reaction sites, by which the recombination of photoinduced charge carriers can be suppressed and the adsorption of reactants and the SR of nitroarenes can be promoted. The sample loaded with only of 0.03% Pt showed the highest performance and, after irradiation for 4 h, the conversions of p-methoxybenzyl alcohol and nitrobenzene are as high as 92.7% and 94.8%, while the yields of p-methoxybenzaldehyde and aniline are 80.5% and 36.0%. The activities are about 2.0 times higher than that of CdS. The coupling reaction mechanism for the SO of aromatic alcohols to aldehydes and SR of nitroarenes to anilines in the reaction system was finally proposed.

Nano-TiO2-P25-SO3H as a new and robust photo-catalyst: The acceleration effect of selective oxidation of aromatic alcohols to aldehydes under blue LED irradiation

Nano photo-catalyst ‘TiO2-P25-SO3H’ has been synthesized for the first time as a covalently grafted solid acid and used for the oxidation of different aromatic alcohols to the corresponding carbonyl compounds under visible light irradiation (blue LED, λ > 420 nm). This new and efficient nano photo-catalyst has selectively converted primary aromatic alcohols to the corresponding aldehydes in the presence of nitrobenzene as available industrial oxidant with excellent yields. This new powerful nano photo-catalyst provides a green and mild approach for photo-oxidation of alcohols.

Optimizing Pd and Au-Pd decorated Bi2WO6 ultrathin nanosheets for photocatalytic selective oxidation of aromatic alcohols

Ultrathin semiconductor nanosheets decorated with metallic nanoparticles (NPs) are promising in photocatalysis due to the multi-component interactions. The materials with a series of monometallic Pd and bimetallic Au-Pd NPs anchored on Bi2WO6 ultrathin nanosheets were synthesized and developed as photocatalysts for selective oxidation of aromatic alcohols to aromatic aldehyde. By optimizing the metallic contents, a typical sample of Au(0.25)Pd(0.25)-Bi2WO6 exhibited the highest photocatalytic activity among all the prepared photocatalysts including Au(0.5)-Bi2WO6, Pd(x)-Bi2WO6, Au(x)Pd(x)-Bi2WO6 (x represents the weight percentage of metal in the photocatalyst), along with the improved selectivity for producing benzaldehyde. The extended absorption in visible range, higher efficiency for the transfer and separation of photogenerated charge carriers, and the superior ability for generating active radicals of Au(0.25)Pd(0.25)-Bi2WO6 were demonstrated by DRS spectra, photoelectrochemical measurements, and ESR detection. The effect of the active species for selective oxidation of aromatic alcohols was proved to follow the order of h+ + O2− > h+ >> O2−. Accordingly, a possible mechanism based on the interfacial cooperation between bimetallic Au-Pd NPs and Bi2WO6 ultrathin nanosheets was proposed to illustrate the photocatalytic process, where the holes accumulated in Bi2WO6 ultrathin nanosheets and O2− produced on metallic NPs synergistically promote the selective oxidation of aromatic alcohols.

Chalcogenide photocatalysts for selective oxidation of aromatic alcohols to aldehydes using O2 and visible light: A case study of CdIn2S4, CdS and In2S3

CdIn2S4, CdS and In2S3 photocatalysts were fabricated via a facile solvothermal method using indium chloride, cadmium nitrate and thiacetamide as precursors. The physicochemical and optical properties of the as-prepared samples were characterized by a series of techniques. The photocatalytic activities of the as-prepared samples were evaluated by selective aerobic oxidation of aromatic alcohols to corresponding aldehydes under visible light illumination. Compared with pure In2S3 and CdS samples, CdIn2S4 photocatalyst shows superior photocatalytic performance for selective oxidation of benzyl alcohol (BA) to benzaldehyde (BAD). Under the optimal conditions, the conversion and selectivity for photocatalytic selective oxidation of BA to BAD are 80.1 and 98.8% under visible light irradiation for 2 h, respectively. The excellent photocatalytic performance of CdIn2S4 photocatalyst should be ascribed to its unique structure with a favorable absorptivity, appropriate conduction band and valence band positions and longer lifetime of photogenerated charge carriers. A possible reaction mechanism for selective oxidation of BA to BAD over CdIn2S4 photocatalyst with O2 and visible light is proposed. It is hoped that the current work could offer an avenue to prepare high-performance chalcogenide photocatalysts used in the field of photocatalytic selective organic transformations.

Photocatalytic organic transformations: Simultaneous oxidation of aromatic alcohols and reduction of nitroarenes on CdLa2S4 in one reaction system

Photocatalytic selective organic transformations (SOTs) with sunlight offer a “green” route for synthesis of fine chemicals. In this work, a bare ternary chalcogenide CdLa2S4 photocatalyst was fabricated to couple the selective oxidation (SO) of aromatic alcohols to aldehydes and selective reduction (SR) of nitroarenes to anilines in one reaction system. The photocatalyst showed a high stability and a good generality for the conversions due to the well–matched band structure and the high separation efficiency of photoinduced electrons (e–) and holes (h+). For p–substituted aromatic alcohols, the selectivities to the corresponding aldehydes are as high as ca. 90%. The electro–donating substituent in the para position benefits the SO reactions, which are triggered by h+ via a successive deprotonation; while for p–substituted nitroarenes, the SR to the corresponding anilines is vulnerable to the electro–withdrawing groups and the steric hindrance of the substituent and the selectivities to anilines are substantially lower than that of the SO conversions. H+ deprotonated in the SO of aromatic alcohols is indispensable for the SR of nitroarenes as they are achieved by a H+–coupled six e– reduction process, which leads to the low conversion efficiencies. The half conversions not only be coupled by the photoinduced e– and h+, but also collaborate with each other through H+. Our results clearly demonstrate the emerging concept of a coupled reaction system for sunlight–driven synthesis of fine chemicals and reveal the underlying mechanism.

Interfacial synergism of Pd-decorated BiOCl ultrathin nanosheets for the selective oxidation of aromatic alcohols

Pd-decorated BiOCl ultrathin nanosheets exhibited improved photocatalysis for the selective oxidation of aromatic alcohols due to the remarkable interfacial synergism.

Nitrogen vacancy engineered graphitic C3N4-based polymers for photocatalytic oxidation of aromatic alcohols to aldehydes

Vacancy defect in the semiconductors plays an important role in the improvement of the electronic structure and the increase of specific reaction sites for reactant molecules, and consequently enhancing the photocatalytic activity of semiconductor photocatalysts. Through high-temperature thermal condensation of a nitric acid-pretreated melamine precursor, nitrogen vacancies were successfully introduced in the framework of g-C3N4. The nitrogen vacancies located at the uncondensed terminal NHx lattice sites were conducive to the enhancement of optical absorption, the improvement of the separation efficiency of the photogenerated charge carrier and the increase of surface area, which was beneficial to the photocatalytic oxidation process. More significantly, the novel CNNA(X) were used as efficient photocatalysts in the green process of aromatic aldehydes from the photocatalytic selective oxidation of aromatic alcohols and the photocatalytic degradation of organic pollutants. CNNA(X) samples exhibited enhanced photocatalytic activity and excellent recyclability and stability. The 68.3% benzyl alcohol conversion and almost 100% selectivity was observed for the CNNA (0.9) photocatalyst, higher than that of pure g-C3N4. Meanwhile, CNNA (0.9) showed superior photocatalytic degradation performance of organic dyes (RhB and MO). Furthermore, the underlying photocatalytic oxidation mechanism was proposed by the controlled experiments using radical scavengers.

Comparison of selective oxidation of aromatic alcohols using copper(II) chromite-titanium dioxide nanocomposite at reflux, light irradiation, and microwave conditions

ABSTRACTCuCr2O4/TiO2 nanocomposites with different TiO2 contents were synthesized by using sol-gel method. Products were characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Results demonstrated a cubic normal spinel structure for copper (2+) chromite, with the particle sizes of about 25–40 nm. Activities of CuCr2O4 nanopowders and CuCr2O4/TiO2 nanocomposite were tested for oxidation of benzylic alcohols to aldehydes at reflux, light irradiation, and microwave conditions. The influence of some parameters on the oxidation of alcohol, such as optimum molar ratio of chromite to titanium dioxide, catalyst dosage, and type and amount of oxidant and solvents (dichloromethane, acetonitrile, and ethanol) was studied to determine the optimal operating conditions for alcohol oxidation in reflux, light irradiation, and microwave conditions.

Hierarchical yolk-shell WO3 microspheres with highly enhanced photoactivity for selective alcohol oxidations

Hierarchical WO3 microspheres with controllable interior structures from solid, yolk-shell, to hollow were synthesized through sonochemical precipitation and hydrogen ion-exchange routes followed by thermal treatment. During the photocatalytic selective oxidation of aromatic alcohols to their corresponding aldehydes in aqueous medium under light irradiation with full wavelengths, the yolk-shell WO3 microspheres exhibited much higher photocatalytic activity than those WO3 microspheres with solid and hollow structures, respectively. This superior activity of the yolk-shell WO3 microspheres can be attributed to the synergistic promoting effect of the following factors: firstly, the porous structure constructed by self-assembly of the interconnected nanosheets together with high surface area promoted the light harvesting and also facilitated the adsorption and diffusion of reactant molecules; secondly, the small crystallite size favored the rapid transfer of photoelectrons, which diminished the transfer distance of photoelectrons and thus inhibited their recombination with holes; thirdly, the yolk-shell structure enhanced light harvesting via multiple reflections in the yolk-shell chambers. Meanwhile, all the WO3 photocatalysts displayed excellent durability against structural collapse due to the robust hierarchical structures. This work identifies the important role of yolk-shell structure played in photocatalytic selective oxidation of aromatic alcohols.

Synergistic effect of photocatalysis and thermocatalysis for selective oxidation of aromatic alcohols to aromatic aldehydes using Zn3In2S6@ZnO composite

Selective oxidation of aromatic alcohols to corresponding carbonyl compounds under mild conditions has a promising prospect in industry. In the paper, we successfully prepared a new mode of photothermocatalyst, Zn3In2S6@ZnO composite, which shows dramatically enhanced activity for selective oxidation of benzyl alcohol to benzaldehyde compared with single Zn3In2S6 and ZnO under visible light illumination. The enhancement is due to a synergistic effect of low-temperature thermocatalysis on ZnO and photocatalysis on Zn3In2S6. ZnO could weaken bonds of the CHα and the OH. Then the reactive species (O2− and h+) generated on Zn3In2S6 could be easy for selective oxidation of benzyl alcohol to produce benzaldehyde. The photoelectrochemical and photoluminescence (PL) results and a series of control experiments (e.g. reaction temperature and radical scavenger) prove this synergistic effect and proposed mechanism. Moreover, the stable performance and high activity of Zn3In2S6@ZnO for other aromatic alcohols indicate its applicable potential. This study provides a promising way to combine photocatalysis and thermocatalysis for the design of novel and efficient visible-light-driven catalyst for selective oxidation of aromatic alcohols or other organics under mild reaction conditions.

Solvothermal synthesis of CdIn2S4 photocatalyst for selective photosynthesis of organic aromatic compounds under visible light

Ternary chalcogenide semiconductor, cadmium indium sulfide (CdIn2S4), was prepared by a simple solvothermal method using ethylene glycol as a solvent, as well as indium chloride tetrahydrate (InCl3.4H2O), cadmium nitrate tetrahydrate [Cd(NO3)2.4H2O], and thiacetamide (TAA) as precursors. The resulted sample was subject to a series of characterizations. It is the first time to use CdIn2S4 sample as a visible light-driven photocatalyst for simultaneous selective redox transformation of organic aromatic compounds. The results indicate that the as-synthesized CdIn2S4 photocatalyst not only has excellent photocatalytic performance compared with pure In2S3 and CdS for the selective oxidation of aromatic alcohols in an oxygen environment, but also shows high photocatalytic redox activities under nitrogen atmosphere. A possible mechanism for the photocatalytic redox reaction in the coupled system was proposed. It is hoped that our current work could extend the applications of CdIn2S4 photocatalyst and provide new insights for selective transformations of organic compounds.

Singlet Oxygen-Engaged Selective Photo-Oxidation over Pt Nanocrystals/Porphyrinic MOF: The Roles of Photothermal Effect and Pt Electronic State.

The selectivity control toward aldehyde in the aromatic alcohol oxidation remains a grand challenge using molecular oxygen under mild conditions. In this work, we designed and synthesized Pt/PCN-224(M) composites by integration of Pt nanocrystals and porphyrinic metal-organic frameworks (MOFs), PCN-224(M). The composites exhibit excellent catalytic performance in the photo-oxidation of aromatic alcohols by 1 atm O2 at ambient temperature, based on a synergetic photothermal effect and singlet oxygen production. Additionally, in opposition to the function of the Schottky junction, injection of hot electrons from plasmonic Pt into PCN-224(M) would lower the electron density of the Pt surface, which thus is tailorable for the optimized catalytic performance via the competition between the Schottky junction and the plasmonic effect by altering the light intensity. To the best of our knowledge, this is not only an unprecedented report on singlet oxygen-engaged selective oxidation of aromatic alcohols to aldehydes but also the first report on photothermal effect of MOFs.

POM@IL-MOFs – inclusion of POMs in ionic liquid modified MOFs to produce recyclable oxidation catalysts

A novel heterogeneous catalyst for the fast and totally selective oxidation of aromatic alcohols to the corresponding aldehydes.

Amino acid-assisted synthesis of In2S3hierarchical architectures for selective oxidation of aromatic alcohols to aromatic aldehydes

Flowerlike-In2S3photocatalyst was preparedviaa biosynthesis technique and showed high activity toward the selective oxidation of aromatic alcohols.

Comparing the Contribution of Visible-Light Irradiation, Gold Nanoparticles, and Titania Supports in Photocatalytic Nitroaromatic Coupling and Aromatic Alcohol Oxidation

Under visible-light irradiation, gold nanoparticles (Au NPs) supported by titania (TiO2) nanofibers show excellent activity and high selectivity for both reductive coupling of nitroaromatics to corresponding azobenzene or azoxylbenzene and selective oxidation of aromatic alcohols to corresponding aldehydes. The Au NPs act as active centers mainly due to their localized surface plasmon resonance (LSPR) effect. They can effectively couple the photonic energy and thermal energy to enhance reaction efficiency. Visible-light irradiation has more influence on the reduction than on the oxidation, lowering the activation energy by 24.7 kJ mol-1 and increasing the conversion rate by 88% for the reductive coupling, compared to merely 8.7 kJ mol-1 and 46% for the oxidation. Furthermore, it is found that the conversion of nitroaromatics significantly depends on the particle size and specific surface area of supported Au NPs; and the catalyst on TiO2(B) support outperforms that on anatase phase with preferable ability to activate oxygen. In contrast, for the selective oxidation, the effect of surface area is less prominent and Au NPs on anatase exhibit higher photo-catalytic activity than other TiO2 phases. The catalysts can be recovered efficiently because the Au NPs stably attach to TiO2 supports by forming a well-matched coherent interface observed via high-resolution TEM.

Effect of different solvent on the photocatalytic activity of ZnIn2S4 for selective oxidation of aromatic alcohols to aromatic aldehydes under visible light irradiation

A series of ternary chalcogenides, zinc indium sulphide (ZnIn2S4), were synthesized by a simple solvothermal method with different solvents. The structure, textural, and optical properties of the resulting materials were thoroughly characterized by several techniques. The as-prepared ZnIn2S4 samples could all be employed as excellent photocatalysts to activate O2 for selective oxidation of aromatic alcohols to aromatic aldehydes under visible light illumination. The results showed that ZnIn2S4 prepared in ethanol solvent (ZIS-EtOH) exhibited the highest photocatalytic activity among the screened samples. The differences of photocatalytic performance for ZnIn2S4 samples prepared in different media were mainly attributed to the different levels of exposed {0001} special facets caused by the exposure extent of the basic crystal plane. In addition, O2− and positive holes were proved to be the main active species during the photocatalytic process. Combined with the previous reports, a possible photocatalytic mechanism for the selective oxidation of benzyl alcohol to benzaldehyde over ZnIn2S4 sample was proposed.

Visible-light-induced aerobic photocatalytic oxidation of aromatic alcohols to aldehydes over Ni-doped NH2-MIL-125(Ti)

The Ni-doped NH2-MIL-125(Ti) catalyst was developed for the photocatalytic aerobic oxidation of aromatic alcohols upon visible light irradiation. The results show that different aromatic alcohols can be effectively transformed to their corresponding aldehydes with almost absolute selectivity using O2 as the oxidant over Ni-doped NH2-MIL-125(Ti) upon visible light irradiation. Compared with the parent catalyst NH2-MIL-125(Ti), Ni-doped NH2-MIL-125(Ti) exhibits a significantly enhanced photocatalytic activity for the selective oxidation of aromatic alcohols. Preliminary studies indicate that the doping of Ni nanoparticles into NH2-MIL-125(Ti) could improve the visible-light harvesting, charge-separation, and electron-transport of the resultant catalyst, leading to the enhanced photocatalytic activity. The current work provides some guidance in the development of MOF-based photocatalysts for organic syntheses.