Selective Oxidation Of Aromatic Alcohols Research Articles

Metal-free, light assisted integrated CO2 reduction coupled with selective oxidation of alcohols under visible light irradiation

An integrated CO2 photoreduction to CO by photo-induced electrons coupled with selective oxidation of aromatic alcohols to carbonyl compounds by photo-generated holes using metal-free anthraquinone (AQ) as an organo-photocatalyst under visible illumination is described. The maximum conversion of benzyl alcohol to benzaldehyde was 65.6% with a selectivity of 98 %, accompanied with the CO yield in gaseous phase 8.67 μmol h−1 g.−1 DFT calculations indicated that initial binding of benzyl alcohol with AQ formed an intermediate IM1 that subsequently interacted with CO2 to give CO2 anion with a free energy change of 0.24 eV. Further, the reduction of CO2 accompanied with the oxidation of benzyl alcohol provided CO and benzaldehyde, respectively along with the release of a water molecule. This concerted metal-free photocatalytic system offers the efficient use of electron-hole pairs for organic synthesis coupled with the CO2 conversion in a cost-effective and sustainable manner.

Soft-templating synthesis of mesoporous MnSiOx composites as catalytic supports for Pd nanoparticles towards solvent-free oxidation of benzyl alcohol under atmospheric pressure O2

Solvent-free and liquid-phase selective oxidation of aromatic alcohols using O2 as an oxidant is a green strategy for the synthesis of aromatic aldehydes and other carbonyl compounds. Wherein, the design and preparation of heterogeneous catalysts with high activity and selectivity is a hot topic in this process. Herein, a series of manganese oxide-silica (MnSiOx) composites were synthesized using cetyltrimethylammonium bromide as a soft template. During the preparation process, the amounts of tetraethyl orthosilicate and ammonia and the calcination temperature significantly affected the textural properties and Mn cation distributions of MnSiOx. The MnSiOx composites were then employed as catalysts for Pd nanoparticles. In the solvent-free and atmospheric conditions, Pd/MnSiOx materials showed high catalytic conversions of benzyl alcohol (BZA), and the catalytic activity thereof is related to the fractions of Pd0 and Mn3+. As the reaction time and temperature are 4 h and 90 °C, the conversion of BZA (feeding dosage: 4 mL) and the selectivity of benzaldehyde are 64.8 % and 94.9 %, respectively. The catalyst can be reused at least five times without any significant loss of activity. Furthermore, the correlation between physiochemical properties and catalytic activity of Pd/MnSiOx was analyzed.

Understanding contributions of zeolite surface hydroxyl groups over Au/USY in selective oxidation of aromatic alcohols

Metal-zeolites catalysts are of great importance in selective organic conversions. Zeolites possess features of highly-ordered porous network, adjustable acidic properties (Brønsted/Lewis), spatial nanoconfinement effects, unique shape selectivity and the strong (hydrothermal-) stability. The role of zeolite hydroxyl (z-OH) groups, such as bridging ones in Si-O(H)-Al (B acids) and terminal ones in Al-OH and Si-OH (silanols), in catalysis is an interesting topic, particularly when they are not catalytic active sites, while they affect the catalytic performances. This study comprehensively investigated series of Au/USY catalysts in the selective oxidation of benzyl alcohol to benzaldehyde and clarified the dominating contributions of Al-associated z-OH groups to affecting catalytic conversions and selectivity via altering the Si/Al ratio and reducing z-OH groups by amorphous silica species derived from diethoxydimethylsilane under high-temperature calcination. The catalysts were characterized by XRD, BET, TEM, XPS, UV/Vis, FT-IR and in-situ DRIFT to investigate crystal structures, textural properties, morphologies, size distribution, chemical state of gold, acidity, and adsorptive properties. The experimental results proved that zeolites with a higher amount of z-OH groups tuned by Si/Al ratios or by diethoxydimethylsilane silylation exhibited higher catalytic activity because of the adsorption effect. Finally, a possible mechanism was discussed based on the experimental results and literature.

Biomimetic Solar Photocatalytic Reactor for Selective Oxidation of Aromatic Alcohols with Enhanced Solar‐Energy Utilization

AbstractLow utilization of solar energy remains a challenge that limits photocatalytic efficiency. To address this issue, this work proposes a bionic solar photocatalytic reactor (BSPR) for efficient selective oxidation of aromatic alcohols. A biomimetic phototropic hydrogel is prepared by coupling chlorine‐doped polypyrrole (Cl‐PPy) and poly(N‐isopropyl acrylamide) (PNIPAm) to maximize light‐harvesting efficiency automatically, allowing the BSPR to maintain high catalytic levels throughout the day. Molecular dynamics simulations are used to unveil the understanding of the fast photoresponsive behavior of Cl‐PPy/PNIPAm from a molecular level, while COMSOL simulations are conducted to follow the macroscopically phototropic mechanism of BSPR. Attributing to the existence of PdS/S vacancies riched ZnIn2S4 nanocomposite in the top flower‐shaped hydrogel, the BSPR displays a special function for efficiently photocatalytic oxidation of aromatic alcohols under solar illumination (yield of 4‐methoxybenzaldehyde: 479.5 µmol g−1 h−1; selectivity: 68.8%). Two possible reaction pathways are identified as follows: photogenerated holes can attract aromatic alcohols directly and generate aromatic aldehydes; photoexcited electrons oxidize O2 to ·O2− can also react with the adsorbed aromatic alcohol. This study presents a promising paradigm that explores opportunities for enhanced utilization of light energy, offering a novel approach to maximize its efficiency in practical applications.

Some sulphur - containing double combination reagents

Research and development of new reagents are very important for organic synthesis. In recent years, some new reagents with universal applicability have been reported, but new reagents of sulphur-containing are rarely reported. Wang’s group has developed several new sulphur-containing reagents which are called as Wang reagents: Sodium dithionite - tert-Butyl hydroperoxide (Na2S2O4-TBHP). The paper presents the reactions involved in the reagents obtaining and the associated mechanisms. Na2S2O4-TBHP is a new reagent for selective oxidation of aromatic alcohols to aldehydes. Wang reagents have universal applicability in organic synthesis.

Cooperation of ultrathin bowl-shaped scaffolds and oxygen vacancies promoting selective photo-oxidation of aromatic alcohols on layered oxyhalide PbBiO2Cl

Photocatalytic selective oxidation of aromatic alcohols into value-added chemicals has attracted increasing attention. Yet most processes suffer from sluggish charge kinetics, weak O2 affinity, low conversion efficiency and selectivity, which restrict their practical development. Herein, PbBiO2Cl ultrathin bowls (UBs) with rich oxygen vacancies (ROV) were initially fabricated via a combined microemulsion method and in-situ reduction process. The ultrathin bowl-shaped geometry and rich OVs effectively boost light absorption and charge separation. Theoretical results indicate the OVs on PbBiO2Cl not only generate abundant localized electrons, but also afford strong interfacial covalent bonds between O2 and OVs, which can act as atomic-level electron transfer highway and effectively promote the O2 adsorption and activation. As a result, ROV-PbBiO2Cl UBs show a 5.2-fold enhanced activity for aerobic oxidation of alcohols to aldehydes relative to PbBiO2Cl nanoplates (NPs). This work may inspire the design of more open hollow scaffolds with defect engineering for artificial photosynthesis.

Ultrathin ZnIn2S4 Nanosheets-Supported Metallic Ni3FeN for Photocatalytic Coupled Selective Alcohol Oxidation and H2 Evolution

Photocatalytic anaerobic organic oxidation coupled with H2 evolution represents an advanced solar energy utilization strategy for the coproduction of clean fuel and fine chemicals. To achieve a high conversion efficiency, the smart design of efficient catalysts by the right combination of semiconductor light harvesters and cocatalyst is highly required. Herein, we report a composite photocatalyst composed of noble metal-free transition metal nitride Ni3FeN decorated on 2D ultrathin ZnIn2S4 (ZIS) nanosheets for selective oxidation of aromatic alcohols to aldehydes pairing with H2 production. In the composite, ultrathin ZIS serves as a light harvester that greatly shortens the diffusion length of photogenerated charges, while the metallic nitride Ni3FeN acts as an advanced cocatalyst which not only captures the photoelectrons generated from the ultrathin ZIS to promote the charge separation, but also provides active sites to lower the overpotential and accelerate the H2 reduction. The best photocatalytic performance is found on ZIS/1.5% M-Ni3FeN, which shows a H2 generation rate of 2427.9 µmol g−1 h−1 and a benzaldehyde (BAD) production rate of 2460 µmol g−1 h−1, about 7.8-fold as high as that of bare ZIS. This work is anticipated to endorse the exploration of transition metal nitrides as high-performance cocatalysts to promote the coupled photocatalytic organic transformation and H2 production.

Systematic Investigation on Supported Gold Catalysts Prepared by Fluorine-Free Basic Etching Ti3AlC2 in Selective Oxidation of Aromatic Alcohols to Aldehydes.

Conventional methods to prepare supported metal catalysts are chemical reduction and wet impregnation. This study developed and systematically investigated a novel reduction method based on simultaneous Ti3AlC2 fluorine-free etching and metal deposition to prepare gold catalysts. The new series of Aupre/Ti3AlxC2Ty catalysts were characterized by XRD, XPS, TEM, and SEM and were tested in the selective oxidation of representative aromatic alcohols to aldehydes. The catalytic results demonstrate the effectiveness of the preparation method and better catalytic performances of Aupre/Ti3AlxC2Ty, compared with those of catalysts prepared by traditional methods. Moreover, this work presents a comprehensive study on the influence of calcination in air, H2, and Ar, and we found that the catalyst of Aupre/Ti3AlxC2Ty-Air600 obtained by calcination in air at 600 °C performed the best, owing to the synergistic effect between tiny surface TiO2 species and Au NPs. The tests of reusability and hot filtration confirmed the catalyst stability.

Constructing a Photocatalyst for Selective Oxidation of Benzyl Alcohol to Benzaldehyde by Photo-Fenton-like Catalysis.

A photoactive metal-organic framework (MOF), [K(H2O)][Cu(DPNDI)][Cu(DPNDI)(CH3CN)(H2O)] [Cu1.5(DPNDI)1.5H1.5P2W18O62]·2H2O (Cu(Ι)W-DPNDI), was prepared by combining a functional photosensitizer N, N'-bis(4-pyridylmethyl)naphthalene diimide (DPNDI), copper(I) ions, and an oxidation catalyst [P2W18O62]6- into a single framework via a hydrothermal process. Cu(Ι)W-DPNDI exhibited a stable structure, strong light absorption capacity, a suitable band gap, and photoelectric properties, which provided favorable conditions for photocatalysis. In the confined space, the well-aligned Cu(I) ions and POM polyanions played a synergetic effect in the electron-transfer process and reactive oxygen species generation. By coupling photocatalysis and heterogeneous Fenton-like catalysis, Cu(Ι)W-DPNDI displayed high efficiency for the selective oxidation of aromatic alcohols, with up to >99% selectivity and 75% yield.

Additive-free selective oxidation of aromatic alcohols with molecular oxygen catalyzed by a mixed-valence polyoxovanadate-based metal-organic framework.

Selective oxidation of alcohols to aldehydes is an industrially significant chemical transformation. Herein, we report a mixed-valence polyoxovanadate-based metal-organic framework (MOF), (H2bix)5{[Cd(bix)2][VIV8VV7O36Cl]2}·3H2O (V-Cd-MOF), for catalyzing the additive-free oxidation of a series of aromatic alcohols with high selectivity and in nearly quantitative yield to the corresponding aldehydes with O2 as the oxidant. Experimental results, corroborated with density functional theory calculations, indicate that it is the synergistic operation of the dual active sites of the VIV-O-VV building units in the polyoxovanadate cluster that is responsible for the excellent catalytic performance observed: on the one hand, the exposed and readily accessible reduced VIV site is believed to activate O2, resulting in a reactive oxygen species for the subsequent activation and breaking of the substrate's Cα-H bond. On the other hand, the VV site coordinates with the alcoholic O atom to facilitate the cleavage of the O-H bond. The catalyst can be recycled by centrifugation and re-used at least five times with uncompromised performance. To our knowledge, V-Cd-MOF represents the first example of a polyoxometalate-based MOF catalyst for additive-free selective oxidation of alcohol to aldehyde with O2 as an oxidant.

Photothermal synergistic engineering of CeO2 and Au co-modified VO2 for efficient and selective oxidation of aromatic alcohols

The reactions of selective aromatic alcohol oxidation are of great significance to basic research and industrial production, yet still facing some challenges, such as harsh reaction conditions, complex reaction systems and environmental pollution. Herein, Au/VO2/CeO2 (AVO/CeO2), a novel photothermal catalyst was designed for the selective oxidation of aromatic alcohols to aromatic aldehydes. Under atmospheric pressure, the optimized 10% A(0.1%)VO/CeO2 (0.1% Au/VO2 denoted as A(0.1%)VO) displays a yield up to 2726.92 μmol/g/h and a selectivity over 99%. A possible photothermal synergistic catalysis mechanism was also proposed on the base of the physical and chemical characterizations and theoretical calculation results. In the thermal cycle process following Mars-vanKrevelen mechanism, the V5+ and Ce4+ oxidized aromatic alcohols into aromatic aldehydes, and the generated V4+ and Ce3+ were oxidized back to V5+ and Ce4+ by the adsorbed oxygen. In the photocatalytic process, the adsorbed oxygen combined with the photogenerated e– derived from CeO2 to generate •O2– and separated the photogenerated charge effectively. Together with the adsorbed oxygen, •O2– and h+ participated in oxidizing V4+, which further enhanced the aromatic alcohols oxidation. Moreover, the introduced Au nanoparticles further accelerated the separation and transport of photogenerated charge, thus improving the photooxidation performance.

Photocatalytic selective oxidation of aromatic alcohols coupled with hydrogen evolution over CdS/WO3 composites

Simultaneously utilizing photogenerated electrons and holes to convert renewable biomass and its derivatives into corresponding value-added products and hydrogen (H2) is a promising strategy to deal with the energy and environmental crisis. Herein, we report a facile hydrothermal method to construct a direct Z-scheme CdS/WO3 binary composite for photocatalytic coupling redox reaction, simultaneously producing H2 and selectively converting aromatic alcohols into aromatic aldehydes in one pot. Compared with bare CdS and WO3, the CdS/WO3 binary composite exhibits significantly enhanced performance for this photocatalytic coupled redox reaction, which is ascribed to the extended light harvesting range, efficient charge carrier separation rate and optimized redox capability of CdS/WO3 composite. Furthermore, the feasibility of converting various aromatic alcohols to corresponding aldehydes coupled with H2 evolution on the CdS/WO3 photocatalyst is proved and a reasonable reaction mechanism is proposed. It is hoped that this work can provide a new insight into the construction of direct Z-scheme photocatalysts to effectively utilize the photogenerated electrons and holes for photocatalytic coupled redox reaction.

Chemically Bonded α-Fe2 O3 /Bi4 MO8 Cl Dot-on-Plate Z-Scheme Junction with Strong Internal Electric Field for Selective Photo-oxidation of Aromatic Alcohols.

Inferior contact interface and low charge transfer efficiency seriously restrict the performance of heterojunctions. Herein, chemically bonded α-Fe2 O3 /Bi4 MO8 Cl (M=Nb, Ta) dot-on-plate Z-scheme junctions with strong internal electric field are crafted by an in situ growth route. Experimental and theoretical results demonstrate that the internal electric field provides a powerful driving force for vectorial migration of photocharges between Bi4 MO8 Cl and α-Fe2 O3 , and the interfacial Fe-O bond not only serves as an atomic-level charge flow highway but also lowers the charge transfer energy barrier, thereby accelerating Z-scheme charge transfer and realizing effective spatial charge separation. Impressively, α-Fe2 O3 /Bi4 MO8 Cl manifests a significantly improved photocatalytic activity for selective oxidation of aromatic alcohols into aldehydes (Con. ≥92 %, Sel. ≥96 %), with a performance improvement of one to two orders of magnitude. This work presents atomic-level insight into interfacial charge flow steering.

Chemically Bonded α‐Fe2O3/Bi4MO8Cl Dot‐on‐Plate Z‐Scheme Junction with Strong Internal Electric Field for Selective Photo‐oxidation of Aromatic Alcohols

AbstractInferior contact interface and low charge transfer efficiency seriously restrict the performance of heterojunctions. Herein, chemically bonded α‐Fe2O3/Bi4MO8Cl (M=Nb, Ta) dot‐on‐plate Z‐scheme junctions with strong internal electric field are crafted by an in situ growth route. Experimental and theoretical results demonstrate that the internal electric field provides a powerful driving force for vectorial migration of photocharges between Bi4MO8Cl and α‐Fe2O3, and the interfacial Fe−O bond not only serves as an atomic‐level charge flow highway but also lowers the charge transfer energy barrier, thereby accelerating Z‐scheme charge transfer and realizing effective spatial charge separation. Impressively, α‐Fe2O3/Bi4MO8Cl manifests a significantly improved photocatalytic activity for selective oxidation of aromatic alcohols into aldehydes (Con. ≥92 %, Sel. ≥96 %), with a performance improvement of one to two orders of magnitude. This work presents atomic‐level insight into interfacial charge flow steering.

Photocatalytic Anaerobic Oxidation of Aromatic Alcohols Coupled With H2 Production Over CsPbBr3/GO-Pt Catalysts.

Metal halide perovskites (MHPs) have been widely investigated for various photocatalytic applications. However, the dual-functional reaction system integrated selective organic oxidation with H2 production over MHPs is rarely reported. Here, we demonstrate for the first time the selective oxidation of aromatic alcohols to aldehydes integrated with hydrogen (H2) evolution over Pt-decorated CsPbBr3. Especially, the functionalization of CsPbBr3 with graphene oxide (GO) further improves the photoactivity of the perovskite catalyst. The optimal amount of CsPbBr3/GO-Pt exhibits an H2 evolution rate of 1,060 μmol g−1 h−1 along with high selectivity (>99%) for benzyl aldehyde generation (1,050 μmol g−1 h−1) under visible light (λ > 400 nm), which is about five times higher than the CsPbBr3-Pt sample. The enhanced activity has been ascribed to two effects induced by the introduction of GO: 1) GO displays a structure-directing role, decreasing the particle size of CsPbBr3 and 2) GO and Pt act as electron reservoirs, extracting the photogenerated electrons and prohibiting the recombination of the electron–hole pairs. This study opens new avenues to utilize metal halide perovskites as dual-functional photocatalysts to perform selective organic transformations and solar fuel production.

In-situ construction of Bi24O31Br10-decorated self-supported BiOBr microspheres for efficient and selective photocatalytic oxidation of aromatic alcohols to aldehydes under blue LED irradiation

The efficient and selective oxidation of aromatic alcohols into corresponding aldehydes under mild conditions is an encouraging but challenging topic in catalysis chemistry and the chemical industry. Herein, a novel Bi24O31Br10-decorated BiOBr composite was synthesized by an in-situ phase transformation route, in which BiOBr microspheres used as 3D self-supported carriers, and Bi24O31Br10 nanosheets are highly dispersed and anchored on the surface of BiOBr microspheres. The as-synthesized composite photocatalysts showed superior selectivity and conversion efficiency for the photocatalytic oxidation of aromatic alcohols under blue LED irradiation. The excellent catalytic performance of Bi24O31Br10-decorated BiOBr is ascribed to its structural relationship between the two components and the dense heterojunction interface, which exposes more active sites and accelerate the spatial charge carriers’ separation. Based on the identification of reactive species (RS) and density functional theory (DFT) calculations, a two-step oxidation mechanism of aromatic alcohols was proposed. In particular, the respective roles of the reactive species, the reason for the first hydrogen loss of aromatic alcohols, and the effects of different substituents on their selectivity were clarified at the molecular level. It is hoped that this work can provide a feasible paradigm for the spatial structure design of different components in heterojunction catalysts to improve the efficiency and selectivity of photocatalytic reactions.

N-CQDs act as electronic warehouse in N-CQDs/CdS regulate adsorption energy to promote photocatalytic selective oxidation of aromatic alcohols

The benzaldehyde (BAD) produced by the benzyl alcohol (BA) oxidation method is comprehensively applied to food and pharmaceutical fields. However, the selectivity and conversion of photocatalytic selective oxidation of BA in aqueous solution are still far from expectation. Herein, N-CQDs/CdS composites were synthesized by the in-situ precipitation method. N-CQDs served as an "Electronic Warehouse" to boost the separation efficiency of the carrier. The electron transferred from CdS to N-CQDs made electron on the N-CQDs surface enrich, which was conducive to the formation of superoxide radicals (·O2-).·O2- and h+ could efficiently oxidize BA to BAD. In addition, according to density functional theory (DFT), the adsorption energies of BA and BAD on N-CQDs/CdS were distinctly greater than that of CdS. BAD tended to desorb from the 7.5 N-CQDs/CdS surface, and BA preferred to adsorb on the CdS surface. However, BAD was difficult to desorb from the CdS surface, resulting in the poisoning of CdS. 7.5 N-CQDs/CdS exhibited the BA conversion of 60.4% and BAD selectivity of 99%, which was 2.2 times higher than that of original CdS. This work was expected to provide a theoretical basis for improving photocatalyst carrier separation efficiency and alcohol selective oxidation performance.

Au/CeO2 Photocatalyst for the Selective Oxidation of Aromatic Alcohols in Water under UV, Visible and Solar Irradiation

Au nanoparticles supported on CeO2 have been prepared and investigated as photocatalysts for the photocatalytic selective oxidation of benzyl alcohol and 4-methoxybenzyl alcohol to the correspondent benzaldehydes, in aqueous suspensions and room conditions under UV, visible and natural solar light irradiation. Au nanoparticles have been supported by impregnation (1 and 3 wt.%) on two types of CeO2 (i.e., a commercial one and a home prepared oxide obtained in the presence of NaOH as precipitation agent). The Au impregnated samples showed strong visible radiation absorption at 565–570 nm associated to localized surface plasmon resonance (LSPR). The bare CeO2 samples are activated by UV light and resulted virtually inactive under visible irradiation, whereas the presence of Au improved both the conversion of the alcohols and the selectivity of the reaction towards the aldehyde, giving rise to good results, particularly under visible and natural solar light irradiation. The activity of the materials increased by increasing the Au content.

Revealing the transfer mechanisms of photogenerated charge carriers over g-C3N4/ZnIn2S4 composite: A model study for photocatalytic oxidation of aromatic alcohols with visible light

Semiconductor photocatalysis as an alternative technology has received extensive attention for addressing the worldwide energy and environment issues. However, it is still a great challenge and imperative to profoundly understand the migration mechanisms for achieving the complete utilization of photoexcited charge carriers. In this paper, a series of g-C3N4/ZnIn2S4 heterojunction composites were fabricated by thermal polycondensation and solvothermal methods and then thoroughly characterized by a range of techniques. Photocatalytic selective oxidation of aromatic alcohols to corresponding aldehydes with O2 under visible light irradiation was introduced as a model reaction system to evaluate the photocatalytic performance of the as-prepared samples. The results exhibit that when the main constituent of photocatalyst is ZnIn2S4, the transfer of the photogenerated charge carriers adopts a band-band mechanism in g-C3N4/ZnIn2S4 heterojunction composite. However, when the main constituent of photocatalyst is g-C3N4, the transfer of the photogenerated charge carriers adopts a Z-scheme mechanism. Therefore, the different compositions of the composite samples lead to the different electronic conductivities and then affect the direction of the built-in electric field in the relative p-n junction, finally causing the different transfer mechanisms of the photogenerated charge carriers for g-C3N4/ZnIn2S4 composite samples.

Sonochemical synthesis of highly efficient Ag3PO4-Guar gum nanocomposite with photo-oxidation property under visible light irradiation

The selective oxidation of aromatic alcohols to aldehyde in an energy-efficient and environmentally benign route remains a challenge. In this study, cubical Ag3PO4-guar gum nanocomposite was synthesised by a simple ultrasound assisted co-precipitation method. The crystalline structure, optical absorption, composition and microstructure of nanocomposites were characterised by X-ray diffraction, photoluminescence, UV-Vis diffuse reflectance spectroscopy, FT-IR spectroscopy, field emission scanning electron microscopy and transmission electron microscopy. The surface modification of Ag3PO4-guar gum nanocomposite dramatically enhanced the photocatalytic oxidation activity. The results from characterisation indicated the compact structure, feasibility to control the size of nanocomposite as well as exhibited higher photocatalytic activity and stability towards oxidation of cinnamyl alcohol to cinnamaldehyde. The oxidation efficiency as high as 95% was obtained. Further analysis had revealed that the holes and O2•− species have contributed to photocatalytic oxidation. The regeneration study of the catalyst displays that it could be reused with minimal loss in activity.