An evaluation of the application of a TiO2/ Cu(II)/solar simulated radiation system for selective oxidation of benzyl alcohol derivatives

BACKGROUND: The conversion of hydroxybenzyl alcohols, nitro‐benzyl alcohol and methoxybenzyl alcohols into the corresponding aldehydes is attempted in aqueous solution by Cu(II) (which reduces to Cu(0)), at room temperature, under acidic and deaerated conditions, using TiO₂ solar simulated light photocatalysis. RESULTS: Under the experimental conditions adopted, the yields of the corresponding hydroxyaldehydes, when Cu(II) was completely reduced to Cu(0), were 21.6% for 4‐hydroxybenzaldehyde, 11.5% for 3‐hydroxybenzaldehyde and 20.2% for 2‐hydroxybenzaldehyde. Higher conversions of 2‐methoxybenzyl alcohol and 4‐methoxybenzyl alcohol were recorded relative to unsubstituted benzyl alcohol. A selectivity of 5.2%, at 50% conversion of the substrate, was observed for the oxidation of 4‐nitrobenzyl alcohol to 4‐nitrobenzaldehyde. For high degrees of aromatic alcohols conversion, oxidation of the generated aldehydes to the corresponding benzoic acid derivatives is observed. CONCLUSION: The introduction of substituents into the aromatic alcohols structure changes the photocatalytic oxidation rate and product selectivities with respect to that previously observed for unsubstituted benzyl alcohol. In particular, the presence of both electron donating (hydroxy, methoxy groups) and electron withdrawing (nitrogroup) groups on the aromatic ring of the substrate causes a detrimental effect on the selectivity of the process with respect to the case of benzyl alcohol. © 2012 Society of Chemical Industry     

Highly efficient N-doped magnetic cobalt-graphene composite for selective oxidation of benzyl alcohol

We developed a graphene-directed assembly route to synthesize a hybrid composite by assembling cobalt based framework material ZIF-67 on the graphene oxide (GO). The hybrid composite exhibited excellent catalytic performance in selective oxidation of benzyl alcohol by oxygen molecule with 89.5% conversion and 97.3% benzaldehyde selectivity. The catalyst can be magnetically separated and reused four times without obvious loss in the catalytic activity and selectivity.     

Selective oxidation of olefins and aromatic alcohols with tert‐butylhydroperoxide catalyzed by polymer‐anchored transition‐metal complexes

Three polymer‐anchored metal complexes (Co, Cu, and Pd) were synthesized and characterized. The catalytic performance of these complexes was tested for the oxidation of olefins and aromatic alcohols. These complexes showed excellent catalytic activity and high selectivity. These complexes selectively gave epoxides and aldehydes from olefins and alcohols, respectively. Individually, the effect of various solvents, oxidants, substrate oxidant molar ratios, temperatures, and catalyst amounts for the oxidation of cyclohexene and benzyl alcohol were studied. Under optimized reaction conditions, 96, 81, and 71% conversions of cyclohexene and 86, 79, and 73% conversions of benzyl alcohol were obtained with Co(II), Cu(II), and Pd(II) catalysts, respectively. The catalytic results reveal that these complexes could be recycled more than five times without much loss in activity. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Aerobic Oxidation of Benzylic Alcohols in Water by 2,2,6,6‐Tetramethylpiperidine‐1‐oxyl (TEMPO)/Copper(II) 2‐N‐Arylpyrrolecarbaldimino Complexes

Novel copper(II) 2‐N‐arylpyrrolecarbaldimine‐based catalysts for the aerobic oxidation of benzylic alcohols mediated by the 2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPO) radical are reported. The catalytic activity for both synthesized and in situ made complexes in alkaline water solutions was studied revealing high efficiency and selectivity (according to GC selectivity always >99%) for both of these catalytic systems. For example, quantitative conversion of benzyl alcohol to benzaldehyde can be achieved with the in situ prepared bis[2‐N‐(4‐fluorophenyl)‐pyrrolylcarbaldimide]copper(II) catalysts in 2 h with atmospheric pressure of O₂ at 80 °C. Interestingly, these catalysts can utilize dioxygen as well as air or hydrogen peroxide as the end oxidants, producing water as the only by‐product.     

微通道反应器内乙苯连续氧化反应工艺研究

研究了在"心型"结构微通道反应器内乙苯与过氧化氢反应连续合成苯乙酮的氧化工艺过程,考察了乙苯与催化剂醋酸钴的摩尔比、停留时间、溶剂量、反应温度等对单程转化率及选择性的影响。在典型的工艺条件下,n(醋酸钴)∶n(乙苯)=13%,停留时间70 s,促进剂Br/Co=1.75,V(冰乙酸)/V(乙苯)=10∶1,温度为100℃,乙苯的转化率达到30.7%,苯乙酮的选择性达到100%。     

Liquid-phase oxidation of alcohols with oxygen catalysed by modified palladium(II) oxide

Benzyl and trans-cinnamyl alcohols are heterogeneously oxidised to the corresponding aldehydes by O₂ in liquid phase at 100 °C and ambient pressure using hydrous binary Pd^II–M oxides (M=Co^III, Fe^III, Mn^III and Cu^II) as catalysts. Modification of Pd^II oxide with transition metal cations greatly improves the catalytic activity and selectivity to aldehydes, Co^III and Fe^III being the most effective promoters. In benzyl alcohol oxidation in toluene solution, the Pd–Co system gives 85–100% selectivity to aldehydes at 53–95% alcohol conversion in 15–60 min reaction time. The catalyst can be re-used without loss of its activity and selectivity. The presence of a certain amount of water in the catalysts is essential for their performance. From TGA, the composition of the optimal Pd–Co catalyst can be approximated as PdO·(0.13–1.0)CoO(OH)·(2–3)H₂O. The oxidation of alcohols on Pd–M oxide catalysts is accompanied by transfer hydrogenation and decarbonylation side reactions, which is similar to the oxidation on the palladium metal. This indicates that the oxidation of alcohols on Pd–M oxide catalysts occurs via a dehydrogenation mechanism, with hydrogen being present on the catalyst surface.     

Galvanic deposition of silver on 80‐μm‐Cu‐fiber for gas‐phase oxidation of alcohols

Microstructured Ag‐based catalysts were developed by galvanically depositing Ag onto 80‐μm‐Cu‐fibers for the gas‐phase oxidation of alcohols. By taking advantages including large voidage, open porous structure and high heat/mass transfer, as‐made catalysts provided a nice combination of high activity/selectivity and enhanced heat transfer. The best catalyst was Ag‐10/80‐Cu‐fiber‐400 (Ag‐loading: 10 wt%; Cu‐fiber pretreated at 400 °C in air), being effective for oxidizing acyclic, benzylic and polynary alcohols. For benzyl alcohol, conversion of 94% was achieved with 99% selectivity to benzaldehyde at 300 °C using a high WHSV of 20 h^?1. Computational fluid dynamics (CFD) calculation and experimental result illustrated significant enhancement of the heat transfer. The temperature difference from reactor wall to central line was about 10–20 °C for the Ag‐10/80‐Cu‐fiber‐400, much lower than that of 100–110 °C for the Ag‐10‐Cu‐2/Al₂O₃ at equivalent conversion and selectivity. Synergistic interaction between Cu₂O and Ag was discussed, being assignable to the activity improvement. © 2014 American Institute of Chemical Engineers AIChE J, 60: 1045–1053, 2014     

Novel efficient catalysts based on Ru or Pd oxide for selective liquid-phase oxidation of alcohols with nitrous oxide

Ru^IV–M and Pd^II–M (MCo^III, Fe^III and Mn^III) binary oxides supported on γ-alumina are demonstrated to be novel, active catalysts for selective liquid-phase oxidation of primary and secondary alcohols to, respectively, aldehydes and ketones with nitrous oxide under 10 bar N₂O pressure and 100 °C. The Ru and Pd catalysts have comparable activities but Ru ones are more selective, the Ru–Co system (Ru/Co=1:1) showing the best performance. Activated primary alcohols (benzyl and cinnamyl alcohol) and secondary alcohols give aldehydes or ketones with 100% selectivity at 95–100% conversion. Non-activated primary alcohols (e.g. 1-dodecanol) give aldehydes with some over-oxidation to acids; the latter is completely inhibited by adding a radical scavenger. The Ru–Co catalyst can be reused without loss of selectivity, although with a gradual decrease in its activity. Compared to the Ru–Co catalysed oxidation of alcohols with O₂ studied earlier, the oxidation with N₂O has the advantage of considerably higher selectivity, albeit occurring under higher pressures.     

4-OH-TEMPO radical grafted onto a novel polyaromatic ether sulfone containing carboxyl side chains as solid catalyst for alcohol oxidation

2,2,6,6-Tetramethylpiperidinium-nitroxide (TEMPO) is a mild and efficient catalyst, which is important in the industrial production of selective oxidation of alcohols to the corresponding aldehyde or ketone compounds. However, it is a challenge to recover the expensive TEMPO catalyst in homogeneous catalytic systems. In this study, a novel polymer-supported catalyst was prepared using 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxy (4-OH-TEMPO) and polyaromatic ether sulfone (PAES). The successful grafting of 4-OH-TEMPO in PAES-C was demonstrated by ¹H nuclear magnetic resonance (¹H NMR) and Fourier transform infrared (FT-IR), load capacity can be calculated by elemental analysis (EA). BET and scanning electron microscopy (SEM) to depict the structure-performance relationship. Herein, SEM images revealed the existence of porous structure. This structure can effectively adsorb NO molecules to form a PAES-TEMPO/NO_x catalytic system to selectively oxidize benzyl alcohol. The experimental results indicated the high activity, the subsequent benzyl alcohol oxidation cycle can reach more than 93% conversion without showing a large loss of selectivity. More importantly, the as-prepared catalyst exhibited the attractive recyclability (recovery rate is 98%). After 10 consecutive runs, no significant loss of conversion and selectivity was observed (the conversion rate of benzyl alcohol was more than 93% and the selectivity was more than 95%). This study might provide some recommendation on the development of highly efficient catalysts for alcohol oxidation.     

Efficient and Selective Aerobic Alcohol Oxidation Catalyzed by Copper(II)/2,2,6,6,‐Tetramethylpiperidine‐1‐oxyl at Room Temperature

A simple and efficient copper(II)/2,2,6,6,‐tetramethylpiperidine‐1‐oxyl (TEMPO)‐catalyzed aerobic oxidation of both primary and secondary benzylic, allylic, and aliphatic alcohols to their corresponding aldehydes and ketones at room temperature using the copper(II) complex [Cu(μ‐Cl)(Cl)(phen)]₂ as the Cu(II) source is reported. The conversion of both electron‐rich and electron‐neutral benzyl alcohols is smooth and faster than those of electron‐deficient ones. The chemoselectivity of a primary benzyl alcohol over the secondary alcohol is also observed. Alcohols regarded as difficult substrates for oxidation due to their coordinating ability with transition metal catalyst such as 4‐(methylthio)benzyl alcohol and 3‐pyridinemethanol are also oxidized easily. In addition, a lignin model alcohol is oxidized to the corresponding aldehyde in excellent yield. Conversions of benzylic and allylic alcohols are faster as compared to those of aliphatic alcohols in accordance with their C_α H bond strengths. A plausible mechanism of the TEMPO‐based catalytic cycle is proposed.     

Efficient liquid phase oxidation of olefins and aromatic alcohol catalyzed by reusable polymer anchored Schiff base complexes

BACKGROUND: Heterogenization of homogeneous catalyst has become an interesting process for the catalytic oxidation of olefins and aromatic alcohol. This may provide a new kind of catalyst that is not only friendly to the environment but also exhibits higher thermal and chemical stabilities. RESULTS: Polymer anchored Schiff‐base complexes of iron(III), copper(II) and cobalt(II) have been synthesized and characterized. The catalytic potential of these complexes has been tested for the oxidation of cyclohexene. The effect of varying solvent, oxidant, substrate oxidant molar ratio, temperature and catalyst amount has been studied. Under optimized reaction conditions 91, 88 and 81% conversion of cyclohexene was obtained with Fe(III), Cu(II) and Co(II) catalysts, respectively. Moreover, the oxidation of other substrates, such as styrene, benzylalcohol, toluene and 1‐hexene were also efficiently carried out by these catalysts. CONCLUSION: The immobilized complexes showed excellent catalytic activity along with high selectivity for the oxidation of olefins and alcohols. The catalysts can be recycled more than five times without any noticeable loss of catalytic activity. Copyright © 2009 Society of Chemical Industry     

锰掺杂CeO2-CoO的制备及其催化苯甲醇液相选择性氧化

以硝酸盐作前体,通过均匀共沉淀法制备了掺锰复合氧化物CeO2-MnO2-CoO,采用X-射线粉末衍射(XRD)对复合氧化物进行了表征,并研究了复合氧化物在苯甲醇液相氧化反应中的催化性能.结果表明,复合氧化物的组成、反应时间、溶剂种类和氧化剂用量等对苯甲醇转化率和苯甲醛选择性均有影响.采用叔丁基过氧化氢作氧化剂,正己烷为...     

Continuous gas–liquid aerobic oxidation of toluene catalyzed by [T(p-Cl)PPFe]2O in a series of three stirred tank reactors

The liquid-phase catalytic aerobic oxidation of toluene by [T(p-Cl)PPFe]₂O was studied in a series of three stirred tank reactors. The effects of operation mode (including semi-batch and continuous operation), reaction temperature, catalyst concentration, average residence time, and air flow rate on the oxidation process were examined. The experimental results showed that continuous oxidation had no advantage over the total yield and selectivity of benzaldehyde and benzyl alcohol in comparison with semi-batch oxidation. And the reaction temperature was the most significant factor influencing on continuous oxidation of toluene. It is also found that adopting sequentially decreased temperature in the three series reactors could improve the yield and selectivity of benzaldehyde and benzyl alcohol in this process. Under which at the higher conversion of toluene, the total yield to benzaldehyde and benzyl alcohol increased 17.05% or 43.62% respectively in comparison with adopting sequentially increased or same temperature in the three series reactors.     

Activation of Dioxygen by Cobaloxime and Nitric Oxide for Efficient TEMPO‐Catalyzed Oxidation of Alcohols

The aerobic oxidation of alcohols to their corresponding carbonyl compounds could be efficiently accomplished by using the combination of cobalt nitrate, dimethylglyoxime and 2,2,6,6‐tetramethylpiperidine 1‐oxyl (TEMPO) as a novel catalytic system, and various alcohols including primary and secondary benzylic, allylic and aliphatic alcohols could be quantitatively converted to the corresponding aldehydes or ketones at 70 °C under 0.4 MPa dioxygen pressure in dichloromethane. During the oxidation, the in situ generated cobaloxime and nitric oxide (NO) were responsible for the activation of dioxygen, respectively, thereby, two concerted catalytic routes exist: cobaloxime‐activating‐dioxygen TEMPO‐catalyzed and NO‐activating‐dioxygen TEMPO‐catalyzed aerobic oxidation of alcohols.     

Metal‐Free: An Efficient and Selective Catalytic Aerobic Oxidation of Hydrocarbons with Oxime and N‐Hydroxyphthalimide

A non‐metal catalytic system consisting of dimethylglyoxime (DMG) and N‐hydroxyphthalimide (NHPI) for the selective oxidation of hydrocarbons with dioxygen is described. The synergistic effect of DMG and NHPI ensures its efficient catalytic ability: 82.1% conversion of ethylbenzene with 94.9% selectivity for acetophenone could be obtained at 80 °C under 0.3 MPa of dioxygen in 10 h. Several hydrocarbons were efficiently oxidized to their corresponding oxygenated products under mild conditions.     

硼杂碳包镍负载钯催化芳香醇需氧氧化

以硼杂碳包镍(Ni@BC)为载体,采用乙醇还原前驱体H_2PdCl_4法制备了一种新型磁可分离Pd/Ni@BC催化剂,并对其进行AAS、TEM、XRD和XPS表征,选取苯甲醇需氧氧化为探针反应,考察催化剂用量、反应温度和反应时间对催化性能的影响,研究催化剂对其他芳香醇的催化性能和循环使用性能。AAS结果表明,Pd负载质量分数为9.1%,与理论负载量一致。TEM结果显示,Pd纳米颗粒均匀分散在载体表面,平均粒径为4 nm。XRD和XPS结果均表明,催化剂的活性物种为Pd0。在反应温度80℃、O2_压力101.325 k Pa(流速20 m L·min~(-1))、CH_3CN为溶剂和K_2CO_3为碱性助剂条件下,Pd/Ni@BC对多种芳香醇的氧化反应表现出很高的催化活性和选择性,能将苯甲醇、对甲基苯甲醇、对乙基苯甲醇、对异丙基苯甲醇、肉桂醇、安息香、二苯甲醇以及邻甲基苯甲醇等定量转化为相应的醛或酮。催化剂重复使用5次,苯甲醇转化率由97.3%降至78.9%,Pd的少量脱落和部分氧化是催化剂活性降低的主要原因。     

过渡金属氧化物修饰的金纳米催化剂苯甲醇氧化性能

采用一步法合成介孔二氧化硅负载的金纳米催化剂,以氯化锡为前驱体,通过浸渍法向金纳米催化剂中引入助剂氧化锡,得到过渡金属氧化物修饰的金纳米催化剂。通过N2吸附-脱附、X射线衍射、透射电镜和固体紫外漫反射光谱等对催化剂结构进行表征。将所合成的催化剂用于苯甲醇选择性氧化反应,考察助剂组分对催化剂性能的影响,结果表明,氧化锡的引入改变了金纳米颗粒的表面电子结构,增加了催化剂活性与选择性;但随着氧化锡含量继续增加,催化剂活性降低,这主要是因为金纳米颗粒表面过渡金属氧化物覆盖度增加,减少了催化剂活性组分与苯甲醇的接触。当氧化锡质量分数0.2%时,催化剂效果最佳,在100℃和氧气压力0.2 MPa下反应3 h,苯甲醇转化率25.7%,苯甲醛选择性75.9%,苯甲酸选择性15.8%,苯甲酸苄酯选择性6.3%。     

TEMPO‐Copper(II) Diimine‐Catalysed Oxidation of Benzylic Alcohols in Aqueous Media

In situ generated copper(II)‐diimine complexes combined with TEMPO (2,2,6,6‐tetramethylpiperidinyl‐1‐oxyl radical) were studied in the oxidation of benzylic alcohols, the focus being on enviromentally benign reaction conditions. In this respect, reactions were studied in aqueous alkaline solutions and dioxygen was used as an end oxidant. This simple catalytic system turned out to be highly efficient and selective in the oxidation of primary and secondary benzylic alcohols to their corresponding carbonyl compounds. Under optimised reaction conditions [5 mol % of TEMPO, 3 mol % of copper(II ) diimine, pH 12.6–13.5, 80 °C, 10 bar O₂] benzyl alcohol was quantitatively and selectively oxidised to benzaldehyde. According to ESI‐MS studies, coordination of TEMPO, as well as deprotonated benzyl alcohol to the parent copper‐diimine complex in aqueous solutions is feasible. Supported by these observations a plausible reaction mechanism is proposed for the oxidation reaction.     

NiFe/γ-Al2O3: A universal catalyst for the hydrodeoxygenation of bio-oil and its model compounds

NiFe bimetallic catalyst shows an excellent activity and selectivity for the hydrodeoxygenation (HDO) of three typical model compounds of bio-oil. The conversion of furfuryl alcohol, benzene alcohol and ethyl oenanthate is 100, 95.48 and 97.89% at 400 °C and the yield to 2-methylfuran, toluene and heptane is 98.85, 93.49 and 96.11% at 0.1 ml/min flow speed and atmospheric pressure. It indicates that the major reaction pathway is the cleavage of C–O rather than C–C. After the catalytic HDO of bio-oil over NiFe/Al₂O₃ catalyst, the heating value changes from 37.8 to 43.9 MJ/kg, the pH changes from 6.65 to 7.50.     

Homogeneous Catalytic Hydrogenation of Bio‐Oil and Related Model Aldehydes with RuCl2(PPh3)3

A homogeneous RuCl₂(PPh₃)₃ catalyst was prepared for the hydrogenation of bio‐oil to improve its stability and fuel quality. Experiments were first performed on three model aldehydes of acetaldehyde, furfural and vanillin selected to represent the linear aldehydes, oxygen heterocyclic aldehydes and aromatic aldehydes in bio‐oil. The results demonstrated the high hydrogenation capability of this homogeneous catalyst under mild conditions (55–90 °C, 1.3–3.3 MPa). The highest conversion of the three model aldehydes was over 90 %. Furfural and acetaldehyde were singly converted to furfuryl alcohol and ethanol after hydrogenation, while vanillin was mainly converted to vanillin alcohol, together with a small amount of 2‐methoxy‐4‐methylphenol and 2‐methoxyphenol. Further experiments were conducted on a bio‐oil fraction extracted by ethyl acetate and on the whole bio‐oil at 70 °C and 3.3 MPa. Most of the aldehydes were transformed to the corresponding alcohols, and some ketones and compounds with C–C double bond were converted to more stable compounds.