Aerobic Oxidation Of Benzyl Alcohol Research Articles

Enhancement of photocatalytic aerobic oxidation of benzyl alcohol with the incorporation of cobalt in Zn-based MOF via post-synthetic metal exchange

In this work to introduce Co(II) ions into TMU-22(Zn) metal–organic framework (MOF), we report a postsynthetic exchange (PSE) approach. Several analytical methods were employed to examine the exchange between Co2+ ions and Zn2+ ions in TMU-22(Zn) for the formation of the mixed-metal TMU-22(Zn/Co). It was found that the introduction of active Co2+ ions into the TMU-22(Zn) framework leads to the photocatalytic activity of TMU-22(Zn/Co) for benzyl alcohol oxidation. Since Co2+ ions were favorably substituted at positions more accessible to the substrate, the TMU-22(Zn/Co) showed superior catalytic performance. This study provides a facile method to develop mixed-metal MOFs for photocatalysis performance.

Selective and efficient aerobic oxidation of benzyl alcohols using plasmonic Au-TiO2: Influence of phase transformation on photocatalytic activity

Chemical processes using heterogeneous photocatalytic systems are widely used for the synthesis of valuable fine chemicals. To improve these chemical processes both environmental and energy aspects must be kept in mind for favorable reaction conditions, such as optimum temperature and atmospheric pressure. In this study, plasmonic Au nanoparticles (Au NP) dispersed over TiO2 photocatalyst with different phases of TiO2 (amorphous, anatase and rutile) have been synthesized by using a facile sol–gel method followed by calcination for the photocatalytic oxidation of benzyl alcohol (BnOH) to benzaldehyde (BzH) under visible light irradiation at ambient conditions. The best photocatalyst exhibits high surface area and excellent catalytic conversion efficiency (96%) for the oxidation of BnOH to BzH in less reaction time using a green solvent, acetonitrile at room temperature. The detailed optimization of reaction parameters was performed for alcohol conversion. In addition the corresponding green metrics parameters were also calculated. The photocatalyst also shows excellent stability and reusability for multiple cycles. This work suggests that the Au-TiO2 catalyst provides a novel green and sustainable approach for the selective and efficient aerobic oxidation of BnOH to BzH under visible light irradiation. Furthermore, the impact of different phases of TiO2 on the photocatalytic activity has also been discussed.

Co-N-Si/AC Catalyst for Aerobic Oxidation of Benzyl Alcohols to Esters under Mild Conditions.

A stable, earth-abundant, reusable cobalt-based heterogeneous catalyst is developed for the oxidative esterification of alcohols under ambient conditions, featuring broad substrate scope, providing good to excellent product yields. This protocol enables easy recyclability of the catalyst, measured up to five times without significant loss of efficiency. The active sites of Co-N-Si/AC are proposed to be Co-N species.

Selective aerobic oxidation of benzyl alcohol on inexpensive and reusable ZnO/MnCO3 catalyst

The selective synthesis of benzaldehyde (B) by oxidation of benzyl alcohol (BA) was studied at 373 K using ZnO-MnCO3 catalysts, O2 as oxidant and mild reaction conditions. An inexpensive commercial MnCO3 sample was impregnated with aqueous solutions containing different concentration of Zn2+ cations to obtain a series of ZnO-MnCO3 catalysts with 1.0–22.6 wt% Zn. Catalysts were characterized by N2 physisorption, atomic absorption spectrometry, X-ray diffraction and X-ray photoelectron spectroscopy techniques. Benzaldehyde was selectively formed during liquid phase oxidation of benzyl alcohol but the catalytic performance of the ZnO-MnCO3 materials depended on Zn loading. The maximum initial reaction rate value was measured on the most promising catalyst (15.4 wt% Zn) and a maximum of 88% benzaldehyde yield was achieved on this catalyst after 6 h of reaction using toluene as solvent. The catalytic activity of the ZnO-MnCO3 materials could be assigned to a synergistic contribution of Zn and Mn species. While the main role of ZnO would be related to its capacity to chemisorb the alcohol, the role of highly oxidized Mn surface species (mainly Mn4+) generated during catalyst preparation, is to participate in de redox mechanism involved in benzyl alcohol oxidation toward benzaldehyde. The effect of chemical nature of polar and apolar aprotic solvents was investigated during the aerobic oxidation over 15.4ZnMn. Apolar solvents, in which the oxygen solubility is higher than in the benzyl alcohol, are more suitable for the reaction. An optimum in solvent basicity requirements (hydrogen-bond-acceptance) in order to optimize the catalyst activity was found. The regeneration and reuse of the most promising catalyst were also investigated. A mild thermal treatment at 493 K in flowing air was enough to fully recover the activity of the 15.4ZnO-MnCO3 catalyst.

Palladium-doped hierarchical ZSM-5 for catalytic selective oxidation of allylic and benzylic alcohols

Hierarchical zeolites have the potential to provide a breakthrough in transport limitation, which hinders pristine microporous zeolites and thus may broaden their range of applications. We have explored the use of Pd-doped hierarchical ZSM-5 zeolites for aerobic selective oxidation (selox) of cinnamyl alcohol and benzyl alcohol to their corresponding aldehydes. Hierarchical ZSM-5 with differing acidity (H-form and Na-form) were employed and compared with two microporous ZSM-5 equivalents. Characterization of the four catalysts by X-ray diffraction, nitrogen porosimetry, NH3 temperature-programmed desorption, CO chemisorption, high-resolution scanning transmission electron microscopy, X-ray photoelectron spectroscopy and X-ray absorption spectroscopy allowed investigation of their porosity, acidity, as well as Pd active sites. The incorporation of complementary mesoporosity, within the hierarchical zeolites, enhances both active site dispersion and PdO active site generation. Likewise, alcohol conversion was also improved with the presence of secondary mesoporosity, while strong Brønsted acidity, present solely within the H-form systems, negatively impacted overall selectivity through undesirable self-etherification. Therefore, tuning support porosity and acidity alongside active site dispersion is paramount for optimal aldehyde production.

Base-free selective oxidation of benzyl alcohol in water over palladium catalyst supported on titanium niobate nano sheets

BackgroundExploring catalysts with high-efficiency, stability and mild reaction conditions for oxidation of alcohols is an urgent task. In this work, a simple and efficient nanostructured catalyst system is developed, comprising homogenously dispersed Pd nanoparticles (NPs) with the average sized of 2.84 nm supported on titanoniobate nano sheets. MethodsThe metal precursors are deposited onto the exfoliated TiNbO5 nano sheets through the electrostatic interaction and then reduced to nanoparticles by the UV irradiation. Selective oxidation of benzyl alcohol in ultrapure water was achieved with the as-prepared Pd-TNO under conditions of the base-free and atmospheric pressure with using air as an oxidant. Significant FindingsThe results demonstrate that the catalyst exhibits excellent catalytic activity and selectivity in the aerobic oxidation of benzyl alcohol to benzaldehyde. Furthermore, the catalyst can be reused to five times without significant loss of performance. The nanostructure obtained with the exfoliation/restacking process favors the mass transfer and provides a unique nano reactor during the reaction.

Revealing the Intrinsic Nature of the Synergistic Effect Caused by the Formation of Heterojunctions in Cu-Cu2O/rGO-NH2 Nanomaterials in the Catalysis of Selective Aerobic Oxidation of Benzyl Alcohol.

Ternary nanomaterials Cu-Cu2O/rGO-NH2 (rGO = reduced graphene oxide) exhibited a synergistic effect in the quantitative catalysis of selective aerobic oxidation of benzyl alcohol. The synergistic effect is attributed to the heterojunctions among the three components and in intrinsic nature, the formation of the heterojunctions lowered the conduction band (CB) energy level and raised the valence band (VB) energy level of the main catalyst Cu2O, which eases electron transfer from the catalyst to O2 in its activation and from the substrate to the catalyst in the oxidation, respectively.

The Effect of Alcohol on Palladium Nanoparticles in i-Pd(OAc)2(TPPTS)2 for Aerobic Oxidation of Benzyl Alcohol

In the heterogeneous catalyst i-Pd(OAc)2(TPPTS)2, Pd(II) was reduced to Pd(0) by using different alcohol solvents, and the catalyst’s activity was studied in the aerobic oxidation of benzyl alcohol. We studied the effects of the impregnation time in ethanol as a solvent and the use of various alcoholic solvents on the size of palladium nanoparticles. We found that the reduction of palladium by the various alcohols yielded palladium nanoparticles that were active in the aerobic oxidation of benzyl alcohol. As determined by DLS, TEM, and zeta potential analyses, both the impregnation time in ethanol and the type of alcohol used were observed to affect nanoparticle formation, particle size distribution, and agglomeration, as well as the conversion rate. The palladium nanoparticles’ hydrodynamic diameter sizes obtained during the 24 h of impregnation time were in the range of 10–200 nm. However, following 24 h of impregnation in ethanol the nanoparticles tended to form aggregates. The conversion rates of all the primary alcohols were similar, while for secondary alcohol, in which the hydrogen of the hydroxyl is less acidic and there is steric hindrance, the conversion was the lowest. Performing the oxidation using the solvent 1-propanol yielded smaller nanoparticles with narrower distributions in comparison to the reaction that was observed when using the ethanol solvent. On the other hand, the relatively high particle size distribution in 1-hexanol yielded agglomerates.

Synthesis of Palladium and Copper Nanoparticles Supported on TiO2 for Oxidation Solvent-Free Aerobic Oxidation of Benzyl Alcohol

The use of metal oxides as supports for palladium and copper (Pd–Cu) nanoalloys constitutes a new horizon for improving new active catalysts in very important reactions. From the literatures, Pd-based bimetallic nanostructures have great properties and active catalytic performance. In this work, nanostructures of titanium dioxide (TiO2) were used as supports for Pd–Cu nanoparticles catalysts. Palladium and copper were deposited on these supports using the sol-immobilisation method. The composite nanoalloys were characterized using transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The catalyst was evaluated for the oxidation of benzyl alcohol. The effect of the Cu–Pd ratio using sol-immobilization methods supported on TiO2 was investigated. The results show that monometallic Cu/TiO2 was observed to have a low activity. However, as soon as the catalyst contained any palladium, the activity increased with a significant increase in the selectivity towards isomerization products. The influence of support and temperature were investigated. Furthermore, the catalyst reusability was also tested for oxidation of benzyl alcohol reactions, by repeatedly performing the same reaction using the recovered catalyst. The Pd–Cu/TiO2 catalyst displayed better reusability even after several reactions

Deposition-Precipitation Synthesized CuCo/Activated Carbon Catalysts for Benzyl Alcohol Oxidation Reaction

The effect of Cox addition in the range of 0.1 to 1 mole into Cu supported on activated carbon (AC) catalysts fabricated by deposition-precipitation method was assessed. CuCox/AC prepared via the same method under different calcination temperature was done to evaluate the effect on the properties and activity of the catalysts. The bimetallic Cu-Co catalysts are structurally characterized by X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). It was found that Co was clearly incorporated in Cu/AC lattice and improved the crystalline structure with optimum Co loading. CuCox/AC nanoparticles formed with uniform shapes and size under the present synthesis conditions. The catalytic performances of the as-prepared catalysts were evaluated towards the aerobic oxidation of benzyl alcohol using hydrogen peroxide as oxidant. Cu/AC, Co/AC and CuCox/AC showed ability to oxidize benzyl alcohol to benzaldehyde. CuCo0.2/AC calcined at 450°C showed highest catalytic activity exhibiting 86% conversion of benzyl alcohol due to the high crystallinity as compared to the monometallic counterpart. It was found that the crystallinity of the catalysts could be tuned by varying the amount of Co. The synergistic effects of Cu-Co in optimum mole ratio and calcination temperature influenced the availability of active sites participating in the catalytic activity.

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

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

3D printed catalytic reactors for aerobic selective oxidation of benzyl alcohol into benzaldehyde in continuous multiphase flow

In this work, novel, patterned monolithic reactors were devised to explore more efficient routes for reactant conversion in order to investigate their potential to replace the packed bed and batch reactors conventionally employed in chemical industries. Well-defined bimetallic formulations were developed to substitute platinum group metals and critical raw materials such as palladium and cobalt, at least in part, by less active, but more sustainable and cost-effective metals such as earth-abundant iron. FePd and FeCo based monoliths were 3D printed and stacked in a continuous flow tubular reactor for testing the selective oxidation of benzyl alcohol (BA) into benzaldehyde (BZ) under mild conditions (80–100 °C and atmospheric pressure). The novel monolithic reactors were evaluated against current state-of-the-art reactor technologies, conventional packed bed and batch reactors. The FeCo- and FePd-Al2O3-supported monolithic catalyst beds showed higher conversion and TOF than their packed bed counterparts under the same operating conditions, revealing the impact of the novel design on both regular geometry and composition. What is of particular interest in the catalytic measurements shown is that the combined stacking of two monoliths in a flow reactor, Al2O3-supported Fe and GO-supported FePd catalysts, can significantly improve the performance with an increase in TOF of up to 90% in comparison to their FePd analogues. Mathematical modelling was used to obtain additional insights into the physical and chemical processes governing the rate of BA conversion. It was found that due to the flow regime inside the microchannels, an axial dispersion model was appropriate, which allowed for mapping the concentration profiles of the reactants and products within the respective monolith geometries.

Benzyl alcohol to benzaldehyde oxidation on MnOx clusters: Unraveling atomistic features

• Catalytic oxidation of benzyl alcohol to benzaldehyde over MnO x catalysts is analyzed in the DFT framework. • Oxidation reactivity and selectivity over cluster-sized Mn 4 O 8 and Mn 4 O 9 catalytic models is compared. • Catalyst poisoning is addressed by investigating the formation of benzoic acid following that of benzaldehyde. • Reaction steps and the related oxidation pathways are collected and analyzed by an original kinetic approach. • Experimental strategies aimed at decreasing catalyst deactivation hence at increasing selectivity are proposed. The catalytic oxidation of benzyl alcohol with O 2 is a promising option for the production of benzaldehyde, from both environmental and economical viewpoints. In particular, highly dispersed MnO x systems feature good activity and selectivity in a wide range of temperatures, although deactivation phenomena by over-oxidation and/or poisoning of active sites are generally recorded. On this account, a density functional theory study was performed on cluster-sized catalyst models, namely Mn 4 O 8 and over-oxygenated Mn 4 O 9 fragments, to predict the reactivity pattern of MnO x catalysts in the selective aerobic oxidation of benzyl alcohol. Several pathways concur to determine the whole reaction process and all of them were compared to unveil the atomistic details of the alcohol oxidation mechanism. Moreover, assuming that the consecutive formation of benzoic acid affects the activity-stability pattern of the MnO x based catalyst, also the benzaldehyde oxidation mechanism was computationally addressed. A systematic comparison of the benzyl alcohol and benzaldehyde oxidation mechanisms on the Mn 4 O 8 and Mn 4 O 9 fragments reveals some experimental strategies to test the reaction mechanisms and design alternative catalytic routes to decrease undesired parasitic reactions leading to catalyst deactivation. The matching structural, energetic and kinetic data are published in the Data in Brief journal [1].

Cerium-photocatalyzed aerobic oxidation of benzylic alcohols to aldehydes and ketones.

We have developed a cerium-photocatalyzed aerobic oxidation of primary and secondary benzylic alcohols to aldehydes and ketones using inexpensive CeCl3·7H2O as photocatalyst and air oxygen as the terminal oxidant.

Amino-functionalized zirconium and cerium MOFs: Catalysts for visible light induced aerobic oxidation of benzylic alcohols and microwaves assisted N-Alkylation of amines

Herein we report that mixed zirconium-cerium-MOFs with amino-functionalized linkers (2-amino-1,4-benzenedicarboxylate, BDC-NH2, and 4-aminonaphthalene-2,6-dicarboxylate, NDC-NH2) act as effective non-noble-metal-based heterogeneous catalysts, for both the aerobic photooxidation of benzylic alcohols and for the direct microwaves activation N-alkylation of amines with alcohols. The catalytic performance has been studied considering two different approaches: the effect of NH2 functionalized linkers and the effect of hosting CeIII species on Zr-MOFs. Zr- and ZrCe-MOFs resulted efficient visible-light-driven photocatalysts with high stability and considerable recyclability in the photocatalytic selective oxidation of alcohols to aldehydes using molecular oxygen as oxidant. These materials are also effective catalysts for the microwaves-assisted N-alkylation of amines with alcohols yielding selectively the imine (ZrCe-MOF) or the corresponding secondary amine (Ce-MOFs).

Solvent-free aerobic selective oxidation of benzyl alcohol catalyzed by palladium nanoparticles supported on nitrogen-containing ordered mesoporous carbon

A series of nitrogen-containing ordered mesoporous carbon (NOMC) materials have been prepared by a one-pot soft-templating method under an aqueous solution by adopting various nitrogen-containing precursors. The synthesized NOMC materials were utilized as catalyst supports to load palladium (Pd). The ordered mesostructures of NOMC have been reserved after the loading of Pd, and Pd nanoparticles were well dispersed on the surface of NOMC materials. The analytic results of XPS confirmed that the supported Pd species existed mainly in the form of metallic Pd (Pd0) and there was a probable interaction between Pd and nitrogen species of NOMC. In the solvent-free aerobic oxidation of benzyl alcohol, the Pd/NOMC materials demonstrated high catalytic activities, affording a maximum yield of benzaldehyde up to 95% at 95 °C of reaction temperature.

Selective aerobic oxidation of benzylic and allylic alcohols catalyzed by Cu(OAc)2/TEMPO/Et2NH

Selective oxidation of benzylic and allylic alcohols to their corresponding aldehyde/ketone derivative without affecting saturated alcohols is still a challenging endeavor in organic synthesis. Various metal complexes, especially the copper complexes in the presence of TEMPO are being used very often for such transformations under aerobic conditions, but they are not selective to allylic and benzylic alcohols. The use of copper salt for oxidation of alcohols in the absence of a ligand are very scarcely studied except for the one catalyzed by CuCl/TEMPO where chloride inhibition and lack of selective oxidation have been noted upon use of CuCl 2 . Herein we report a Cu(OAc) 2 catalyzed and TEMPO mediated selective aerobic oxidation of benzylic and allylic alcohols to aldehyde/ketone in the presence of Et 2 NH. The method avoids pre-synthesis of the catalyst as in the case of Cu(II)/(I) complexes/TEMPO catalyzed oxidation reactions, requires low catalyst loading, employs cheaper copper salt, and gives excellent selectivity for oxidation of benzylic and allylic alcohols.

A meso-scale ultrasonic milli-reactor enables gas–liquid-solid photocatalytic reactions in flow

The handling of solid reagents, catalysts and by-products is a daunting challenge in continuous-flow micro- and milli-reactors. Suspensions tend to settle over time leading to irrevocable clogging of the reaction channels. Herein, we describe our efforts to develop an ultrasonic milli-reactor which can handle such challenging solid-containing transformations. The reactor consists of a Langevin-type transducer, a sonotrode and an irradiating cylinder, on which a coiled glass capillary (12.88 mL) was attached. The ultrasonic milli-reactor was combined with an LED illuminating box and its efficacy was showcased in the photocatalytic aerobic oxidation of benzyl alcohol enabled by TiO2 particles exposed to UV-A irradiation. Ultrasound irradiation generates cavitation bubbles and causes a vigorous oscillation of both the cavitation and the Taylor bubbles. This improves the liquid mixing, the gas–liquid mass transfer and ensures resuspension of the settled particles. Moreover, these effects enhance the photon absorption by the semiconductor catalyst, which has an overall positive effect on the photocatalytic transformation.

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

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

Catalytic Oxidation of Benzyl Alcohol to Benzaldehyde on Au8 and Au6Pd2 Clusters: A DFT Study on the Reaction Mechanism

Density functional theory calculations were performed to investigate the reaction mechanism of the aerobic oxidation of benzyl alcohol to benzaldehyde catalyzed by Au and Au–Pd clusters. Two consecutive reaction mechanisms were examined with Au8 and Au6Pd2 clusters: (1) the oxidation of benzyl alcohol with dissociated O atoms on metal clusters generating benzaldehyde and H2O; and (2) oxidation with adsorbed oxygen molecules generating benzaldehyde and H2O2. The calculations show that the aerobic oxidation of benzyl alcohol energetically prefers to proceed in the former mechanism, which agrees with the experimental observation. We demonstrate that the role of Au centers around the activation of molecular oxygen to peroxide-like species, which are capable of the H–abstraction of benzyl alcohol. The roles of Pd in the Au6Pd2 cluster are: (1) increasing the electron distribution to neighboring Au atoms, which facilitates the activation of O2; and (2) stabilizing the adsorption complex and transition states by the interaction between positively charged Pd atoms and the π-bond of benzyl alcohol, both of which are the origin of the lower energy barriers than those of Au8.