Solvent-free Oxidation Of Benzyl Alcohol Research Articles

Selective oxidation using supported gold bimetallic and trimetallic nanoparticles

Supported gold nanoparticles are highly effective for a range of redox reactions. In these reactions the activity is often enhanced by the addition of a second or indeed a third metallic component. A model reaction that is often investigated is the selective oxidation of benzyl alcohol using molecular oxygen as terminal oxidant. In the presence of a solvent the complexity of this reaction can often be missed. However, in the solvent-free oxidation of benzyl alcohol to benzaldehyde using supported gold palladium nanoparticles as catalysts, there are two pathways to the principal product, benzaldehyde. One is the direct catalytic oxidation of benzyl alcohol to benzaldehyde by O2, while the second is the disproportionation of two molecules of benzyl alcohol to give equal amounts of benzaldehyde and toluene. The formation of toluene is an unwanted side reaction. In this paper the research on this reaction will be reviewed and two strategies described that can be used to switch off the formation of the non desired toluene. The first involves the use of basic supports for the gold palladium nanoparticles, which is highly effective in suppressing the formation of toluene and this may be related to the morphology of the gold palladium nanoparticles and their interaction with the support. The second involves the introduction of platinum to the gold palladium nanoparticles which also switches off toluene formation on supports that permit toluene formation in the absence of platinum. This effect may be related to the relative stability of platinum hydride.

Synthesis of ordered mesoporous silica/ceria–silica composites and their high catalytic performance for solvent-free oxidation of benzyl alcohol at room temperature

Ordered mesoporous Ce-MCM-41 and Ce-MCM-48 were prepared in which cerium was incorporated up to 29% of Ce/Si. These materials exhibit outstanding efficiency for highly selective solvent-free liquid phase oxidation of benzyl alcohol to benzaldehyde at room temperature.

ChemInform Abstract: Palladium Supported on an Acidic Metal—Organic Framework as an Efficient Catalyst in Selective Aerobic Oxidation of Alcohols.

Highly dispersed palladium nanoparticles were deposited on an acidic MOF (MIL-101) by using a simple colloidal method. The resulting Pd/MIL-101 catalyst was highly active in the liquid-phase aerobic oxidation of a wide range of alcohols including benzyl, allylic, aliphatic and heterocyclic alcohols as well as diols, affording the desired oxidation products in high yields under base-free and mild conditions. The catalyst was shown to be able to efficiently catalyze aerobic oxidation even at ambient temperature using air instead of pure O2. The solvent-free oxidation of benzyl alcohol gave a remarkably high turnover frequency (TOF) of approximately 16 900 h−1. However, the catalytic activity was significantly suppressed when ethylenediamine was grafted on the uncoordinated Cr sites of the MIL-101 support, which suggests that the open Cr sites might play an important role in promoting the oxidation of alcohols in the present catalytic system.

Au–Pd nanoalloys supported on Mg–Al mixed metal oxides as a multifunctional catalyst for solvent-free oxidation of benzyl alcohol

Au-Pd nanoalloys supported on Mg-Al mixed metal oxides prepared using sol-immobilisation are found to be highly efficient and reusable catalysts for the solvent-free oxidation of benzyl alcohol using molecular oxygen under low pressure. When using this support alloying Pd with Au resulted in an increase in both activity and selectivity to benzaldehyde and moreover an improved resistance to catalyst deactivation compared with the monometallic Pd and Au catalysts. The turnover number for the Au/Pd 1:1 molar ratio catalyst achieved 13,000 after 240 min and the selectivity to benzaldehyde was maintained at 93%; this high catalytic activity can be retained in full after three successive uses. The ensemble and electronic effect of Au-Pd nanoalloys were studied by IR spectroscopy using CO chemisorption, XPS and HRTEM. Moreover, the bifunctional nature of the acid-base MgAl-MMO support was found to be important as the acid sites are considered to be responsible for the improvement of catalytic activity; while, the basic sites gave rise to high selectivity. A possible mechanism with Au-Pd nanoparticles as the active sites has been proposed, illustrating that the oxidation of benzyl alcohol can proceed through the cooperation between the Au-Pd nanoalloys and the base/acid sites on the surface of the support.

Palladium supported on an acidic metal–organic framework as an efficient catalyst in selective aerobic oxidation of alcohols

Highly dispersed palladium nanoparticles were deposited on an acidic MOF (MIL-101) by using a simple colloidal method. The resulting Pd/MIL-101 catalyst was highly active in the liquid-phase aerobic oxidation of a wide range of alcohols including benzyl, allylic, aliphatic and heterocyclic alcohols as well as diols, affording the desired oxidation products in high yields under base-free and mild conditions. The catalyst was shown to be able to efficiently catalyze aerobic oxidation even at ambient temperature using air instead of pure O2. The solvent-free oxidation of benzyl alcohol gave a remarkably high turnover frequency (TOF) of approximately 16 900 h−1. However, the catalytic activity was significantly suppressed when ethylenediamine was grafted on the uncoordinated Cr sites of the MIL-101 support, which suggests that the open Cr sites might play an important role in promoting the oxidation of alcohols in the present catalytic system.

Pd Nanoparticles on Layered Double Hydroxide as Efficient Catalysts for Solvent-Free Oxidation of Benzyl Alcohol Using Molecular Oxygen: Effect of Support Basic Properties

Pd nanoparticles supported on basic layered double hydroxide (LDH) as highly efficient and reusable catalysts are prepared and characterized. The layered structure of LDH support could be reconstructed to different extent by controlling the activation conditions, which presented changing quantity of Bronsted-base sites. Besides, with the changing calcination temperature the LDH substrate imposed a restricted nano-size effect on the supported Pd particles under identical reduction condition, which demonstrated a convenient approach for controlling the size of supported Pd particles. The resulting Pd/LDH samples were tested as heterogeneous catalysts for solvent-free oxidation of benzyl alcohol using molecular oxygen. The sample with a larger amount of Bronsted-base sites is more active in the oxidation of benzyl alcohol, and after five catalytic runs it still gives benzaldehyde in excellent yields. The promotional effect of Bronsted-base sites of the LDH support on the catalytic activity for benzyl alcohol oxidation over Pd/LDH is studied.

Amino-containing cross-linked ionic copolymer-anchored heteropoly acid for solvent-free oxidation of benzyl alcohol with H2O2

Abstract Amino-containing cross-linked ionic copolymer-anchored HPA catalysts were prepared by the anion-exchange of polydivinylbenzene/amino-functionalized ionic liquids copolymers with Keggin heteropoly acid (HPA), and were characterized by 1H NMR, FT-IR, TG, XRD, SEM, TEM, BET surface area, and elemental analysis. Their catalytic performance for oxidation of benzyl alcohol with H2O2 was studied under solvent-free conditions. The results demonstrated that the catalysts were very active and selective, and could be reused after simple separation.

Facile Method for the Synthesis of Phosphomolybdic Acid Supported on Zirconia–Ceria Mixed Oxide and Its Catalytic Evaluation in the Solvent-Free Oxidation of Benzyl Alcohol

A series of phosphomolybdic acid (5–20 wt % PMA) promoted zirconia–ceria (ZrO2–CeO2) mixed oxides were synthesized by an impregnation method and characterized by XRD, nitrogen adsorption/desorption, UV–vis DR spectroscopy, TPR/TPD, and 31P MAS NMR spectroscopy. NMR spectra revealed that the catalyst retained the Keggin structure of PMA even after calcination at 500 °C. The catalysts were screened for the solvent-free liquid-phase oxidation of benzyl alcohols using hydrogen peroxide as the oxidizing agent. The sample of 15 wt % PMA/ZrO2–CeO2 showed 85% conversion and 96% selectivity to the corresponding aldehydes.

Amino functionalized bipyridine–heteropolyacid ionic hybrid: A recyclable catalyst for solvent-free oxidation of benzyl alcohol with H2O2

A new amino-functionalized bipyridine–heteropolyacid ionic hybrid was prepared by protonating and anion-exchanging the amino-attached bipyridine ionic liquid with phosphotungstic acid, and characterized by FT-IR, 1H NMR, UV–vis, XRD, SEM, TG, BET surface area, melting point, and elemental analysis. Its catalytic activity was evaluated in the oxidation of benzyl alcohol with aqueous H2O2. The hybrid catalyst is proved to be a highly efficient solid catalyst for solvent-free oxidation of benzyl alcohol with H2O2, which is featured by the fast reaction rate, high conversion and selectivity, easy recovery, and quite steady reuse.

Palladium nanoparticles supported on manganese oxide–CNT composites for solvent-free aerobic oxidation of alcohols: Tuning the properties of Pd active sites using MnOx

The manganese oxide-multi-walled carbon nanotube (MnOx/CNT) composite was successfully synthesized following a surface deposition method. Subsequently, the palladium nanoparticles were homogeneously deposited onto this MnOx/CNT hybrid material followed by being reduced under H2 atmosphere. The catalytic activity in solvent-free benzyl alcohol oxidation was correlated with MnOx loading, indicating the important role of manganese oxide in tuning the properties of Pd catalytic active site, e.g., dispersion and electron density. In the presence of reducible MnOx on CNT, the electron transfer and oxygen activation were greatly enhanced because of the synergistic interaction between Pd metallic nanoparticles and the hybrid support materials. Due to this strong metal support interaction (SMSI), the Pd/MnOx/CNT catalysts were remarkably stable against deactivation.

Oxidation of Benzyl Alcohol by using Gold Nanoparticles Supported on Ceria Foam

The efficacy of using cerium oxide foams as a support for Au nanoparticles and subsequent use as oxidation catalysts have been investigated. These were synthesized using L-asparagine to produce a cerium coordination polymer foam, which was calcined to give the oxide foam. Au nanoparticles were supported on the CeO(2) foams using a sol-immobilization method. The activity of the Au/foamCeO(2) for solvent-free benzyl alcohol oxidation was superior to standard Au/CeO(2) catalysts, and the activity was found to be dependent on the crystallization time of the precursor foam. A crystallization time of 4 h was found to produce the most active catalyst, which retained activity and a high selectivity to benzaldehyde (ca. 96 %) when re-used and this is related to the structure of the material. The high activity is attributed to the greater lability of surface oxygen in the support compared with commercial CeO(2) materials.

Synthesis of Nickel Hexacyanoferrate Nanoparticles and Their Potential as Heterogeneous Catalysts for the Solvent-Free Oxidation of Benzyl Alcohol

Nickel hexacyanoferrate nanoparticles were synthesized and characterized using elemental analysis, thermal analysis, infrared spectroscopy, and X-ray diffraction. A FE-SEM image of the nickel hexacyanoferrate showed that it consists of nearly spherical particles with sizes ranging from 30 to 70 nm. The synthesized material was found to be a heterogeneous catalyst useful for the solvent-free oxidation of benzyl alcohol with H 2 O 2 as an oxidant. A 36% conversion of benzyl alcohol to benzaldehyde was achieved under optimized reaction conditions using specific parameters such as the amount of catalyst, the temperature, the benzyl alcohol to H 2 O 2 molar ratio, and the reaction time. Nickel hexacyanoferrate nanoparticles were synthesized and used as heterogeneous catalysts for the solvent-free oxidation of benzyl alcohol with H 2 O 2 as an oxidant.

Controlling the Duality of the Mechanism in Liquid‐Phase Oxidation of Benzyl Alcohol Catalysed by Supported Au–Pd Nanoparticles

In the solvent-free oxidation of benzyl alcohol to benzaldehyde using supported gold-palladium nanoparticles as catalysts, two pathways have been identified as the sources of the principal product, benzaldehyde. One is the direct catalytic oxidation of benzyl alcohol to benzaldehyde by O(2), whereas the second is the disproportionation of two molecules of benzyl alcohol to give equal amounts of benzaldehyde and toluene. Herein we report that by changing the metal oxide used to support the metal-nanoparticles catalyst from titania or niobium oxide to magnesium oxide or zinc oxide, it is possible to switch off the disproportionation reaction and thereby completely stop the toluene formation. It has been observed that the presence of O(2) increases the turnover number of this disproportionation reaction as compared to reactions in a helium atmosphere, implying that there are two catalytic pathways leading to toluene.

Magnesium oxide supported nano-gold: A highly active catalyst for solvent-free oxidation of benzyl alcohol to benzaldehyde by TBHP

Nano-size gold particles deposited on MgO by the homogeneous deposition–precipitation showed very high catalytic activity with nearly 100% conversion of benzyl alcohol in a short reaction period (0.5 h) and more over showed excellent reusability in the process. Influence of the catalyst support (MgO, CaO, BaO, SrO, Al2O3, Ga2O3 and In2O3), method of gold deposition, Au loading and catalyst calcination temperature and also that of the reaction conditions (viz. reaction time and temperature) on the benzyl alcohol to benzaldehyde oxidation have been thoroughly investigated.

Growth of zinc hexacyanoferrate nanocubes and their potential as heterogeneous catalyst for solvent-free oxidation of benzyl alcohol

Zinc hexacyanoferrate nanocubes have been synthesized following an extremely simple method and characterized by elemental analysis, thermal analysis, infrared spectroscopic and X-ray diffraction techniques. Field emission scanning electron microscopic image showed that it consisted of sharp cubic particles with size ranging from 83 to 164 nm. Catalytic activity of nanocubic zinc hexacyanoferrate has been studied for solvent-free oxidation of benzyl alcohol using H 2O 2 as oxidant under the optimum conditions of certain parameters such as benzyl alcohol to H 2O 2 molar ratio, the amount of catalyst, reaction time and temperature.

Solvent-free oxidation of benzyl alcohol using Au–Pd catalysts prepared by sol immobilisation

We report the preparation of Au-Pd nanocrystalline catalysts supported on TiO(2) and carbon prepared via a sol-immobilisation technique using three different preparation strategies; namely, simultaneous formation of the sols for both metals or initial formation of a seed sol of one of the metals followed by a separate step in which a coating sol of the second metal is added. The catalysts have been structurally characterised using a combination of transmission electron microscopy and X-ray photoelectron spectroscopy. The catalysts have been evaluated for the oxidation of benzyl alcohol under solvent-free conditions. The catalysts prepared using the sol immobilisation technique show higher activity when compared with catalysts prepared by impregnation, particularly as lower metal concentrations can be used. The Au-Pd catalysts were all more active than the corresponding monometallic supported Au or Pd catalysts. For 1 wt% Au-Pd/TiO(2) the order of metal addition in the preparation was not observed to be significant with respect to selectivity or activity. However, the 1 wt% Au-Pd/carbon catalysts are more active but less selective to benzaldehyde than the TiO(2)-supported catalysts when compared at iso-conversion. Furthermore, for the carbon-supported catalyst the order of metal addition has a very marked affect on activity. The carbon-supported catalysts are also more significantly affected by heat treatment, e.g. calcination at 400 degrees C leads to the activity being decreased by an order of magnitude, whereas the TiO(2)-supported catalysts show a 50% decrease in activity. Toluene is observed as a by-product of the reaction and conditions have been identified that minimise its formation. It is proposed that toluene and benzaldehyde are formed by competing parallel reactions of the initial benzyl intermediate via an adsorbed benzylidene species that can either be hydrogenated or oxidised. Hence, conditions that maximise the availability of oxygen on the catalyst surface favour the synthesis of benzaldehyde.

Solvent-free oxidation of benzyl alcohol over chromium orthoborate

Abstract The use of CrBO 3 in the catalytic liquid phase oxidation of benzyl alcohol (BzOH) has been investigated for the first time. The reaction was performed under solvent-free conditions without employing any oxidant. Benzaldehyde (BzH), dibenzyl ether (DBzE) and benzyl benzoate (BzB) were obtained as the major reaction products. Influence of the reaction parameters (reaction time, temperature and the amount of catalyst) on the catalytic performance has been studied. A mechanism operating over acidic boron sites has been suggested.

A new route to synthesis of sulphonato-salen-chromium(III) hydrotalcites: Highly selective catalysts for oxidation of benzyl alcohol to benzaldehyde

The Mg–Al layered-double hydroxides (LDHs) intercalated by three kinds of sulphonato-salen-chromium(III) complexes were prepared and characterized by FTIR, UV–vis, XRD and elemental analysis. It was found that the homogeneous complexes were successfully intercalated into the LDH interlayer via the method of anion exchange followed by coordination with chromium(III) chloride. And the resulting LDH hosted chromium complexes were shown to be effective heterogeneous catalysts for the solvent-free oxidation of benzyl alcohol (BzOH) to benzaldehyde (BzH) using 30% H 2O 2 as oxidant. Furthermore, owing to the different local environment of the central metal ion chromium(III), the catalyst with the backbone of o-C 6H 4 displayed the highest catalytic performance followed by the NH(CH 2CH 2) 2 with the (CH 2) 2 showing the lowest BzH yield. In addition, a tentative mechanism was also discussed.

Microwave-accelerated solvent-free aerobic oxidation of benzyl alcohol over efficient and reusable manganese oxides

Abstract A new facile and cost-effective process involving the solvent-free oxidation of benzyl alcohol using molecular oxygen as oxidant under controlled microwave irradiation has been developed for the production of chlorine-free benzaldehyde. Influence of different catalyst parameters (different manganese oxides and other kinds of transition metal oxides) and reaction conditions (reaction period and temperature) on the process performance has been studied. Under optimized reaction conditions, the MnO 2 catalyst showed a superior catalytic performance in the highly selective oxidation of benzyl alcohol as compared to other manganese oxide materials such as MnO, Mn 2 O 3 and Mn 3 O 4 . Moreover, a very stable catalytic activity as a function of cycling test was observed for the MnO 2 catalyst.

Solvent-free oxidation of benzyl alcohol using titania-supported gold–palladium catalysts: Effect of Au–Pd ratio on catalytic performance

The oxidation of benzyl alcohol with molecular oxygen under solvent-free conditions has been investigated using a range of titania-supported Au–Pd alloy catalysts to examine the effect of the Au–Pd ratio on the conversion and selectivity. The catalysts have been compared at high reaction temperature (160 °C) as well as at 100 °C, to determine the effect on selectivity since at lower reaction temperature the range of by-products that are formed are limited. Under these conditions the 2.5 wt.% Au–2.5 wt.% Pd/TiO 2 was found to be the most active catalyst, whereas the Au/TiO 2 catalyst demonstrated the highest selectivity to benzaldehyde. Toluene, formed via either a hydrogen transfer process or an oxygen transfer process, was observed as a major by-product under these forcing conditions.