- Fourier Transform Infrared Studies of the Self-Reaction of CH3O2 Radicals
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Product studies were made with the FT IR method in the photooxidation of CH3N2CH3 and in the Cl-atom initiated oxidation of CH4 in O2-N2 mixtures at 700 torr and 297 K.The major products were CH2O, CH3OH, and CH3O2H in both systems.A weak, broad absorption band centered at 1030 cm-1 was assigned tentatively to CH3O2CH3.These results are consistent with the following primary and secondary reactions: (primary) 2CH3O2 ---> 2CH3O + O2 (1a); 2CH3O2 ---> CH3OH + CH2O + O2 (1b); 2CH3O2 ---> CH3O2CH3 + O2 (1c); (secondary) CH3O + O2 ---> CH2O + HO2 (5); CH3O2 + HO2 ---> CH3O2H + O2 (6).The relative rate costants for reactions 1a-c were determined to be k1a:k1b:k1c = 0.32 : 0.60 : 0. 08, respectively.
- Niki, H.,Maker, P. D.,Savage, C. M.,Breitenbach, L. P.
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- A product yield study of the reaction of HO2 radicals with ethyl peroxy (C2H5O2), acetyl peroxy (CH3C(O)O2), and acetonyl peroxy (CH3C(O)CH2O2) radicals
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Branching ratios for HO2 and RO2 reaction were measured for three organic peroxy radicals: ethyl peroxy, acetyl peroxy, and acetonyl peroxy radicals. In the absence of methanol, yields of acetaldehyde and ethyl hydroperoxide (EHP) were 47 and 35%, respectively. In the presence of equal concentrations of ethane and methanol, the acetaldehyde yield dropped to zero, and the EHP yield rose to 93%. Cl atoms reacted with acetaldehyde in the presence of O2 to form acetyl peroxy radicals. The observed paracetic acid and acetic acid were formed almost exclusively in the reaction of acetyl peroxy radicals with H2O2. In the absence of methanol, Cl atoms reacted with acetone to form acetonyl peroxy radicals, which then predominantly reacted with other peroxy radicals present to form acetonoxy radicals. Simulations showed that chain propagation in RO2+HO2 reactions might have a small impact on tropospheric chemistry under low NOx conditions. The impact of these reactions on OH radical concentrations would be greater for aged air, which typically contains higher concentrations of oxygenated organics and lower levels of NOx.
- Hasson, Alam S.,Tyndall, Geoffrey S.,Orlando, John J.
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- Catalytic oxidation of methane to methyl hydroperoxide and other oxygenates under mild conditions
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Methane is oxidized by air in acetonitrile solution to give methyl hydroperoxide (easily reduced to methanol), formaldehyde and formic acid in the presence of [NBu4]VO3-pyrazine-2-carboxylic acid as the catalyst and H2O2 as a promoter.
- Nizova, Galina V.,Suess-Fink, Georg,Shul'pin, Georgiy B.
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- Selective oxidation of methane to methanol using AuPd@ZIF-8
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Selective methane conversion to alcohol derivatives remains an open challenge. Here, bimetallic catalyst, AuPd@ZIF-8, has been synthesized and demonstrated as an excellent catalyst in the presence of H2O2 and O2 under mild
- Sun, Chenghua,Xu, Guowang,Xu, Yongjun,Yu, Aimin
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- Insights into the direct selective oxidation of methane to methanol over ZSM-5 zeolytes in aqueous hydrogen peroxide
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The direct selective oxidation of methane by aqueous hydrogen peroxide over ZSM-5(50) has been investigated. Methyl hydroperoxide was confirmed as the initial product of methane oxidation. The decomposition of methyl hydroperoxide to formaldehyde is established as a key intermediate in an oxidation pathway to formic acid and ultimately CO2. Hydrogen was detected during the oxidation of methane over ZSM-5 zeolites. The hydrogen was evaluated in terms of its origins and possible role in the production of MeOH. The addition of a copper salt to the ZSM-5(50) zeolite was found to decrease the overall productivity of all methane oxygenates. The use of copper also promoted the selectivity for methyl hydroperoxide whilst removing formic acid. The role of hydroxymethyl-methyl hydroperoxide is considered as an intermediate in the decomposition of methyl hydroperoxide to methanol. A tentative proposal into the nature of the iron species responsible for the catalytic species in ZSM-5(50) is made.
- Al-Megren, Hamid,Al-Shihri, Saeed,Chadwick, David,Richard, Christian J.
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- Formation of Molecular Hydrogen by Thermal Decomposition of n-Dialkyl Peroxides in Oxygen
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The decomposition of low concentrations of di-n-butyl, di-n-heptyl, and di-tert-butyl peroxides in presence of oxygen was investigated in the temperature range 150-200 deg C and under atmospheric pressure.It was shown that H2 and H2O2 were simultaneously formed.The ratio /( + ) was practically independent of oxygen concentration, peroxide concentration, and temperature and its value was about 8percent of that for the n-alkyl peroxides.The results are in favor of the formation of H2 and H2O2 by the homogeneous recombination of HO2 radicals.
- Sahetchian, K. A.,Heiss, A.,Rigny, R.
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- FTIR Study of the Kinetics and Mechanism for Cl-Atom-Initiated Reactions of Acetaldehyde
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The rate constant for the reaction Cl + CH3CHO -> CH3CO + HCl was determined to be 7.6 X 10-11 cm3 molecule-1 s-1 at 298 +/- 2 K, using the competitive chlorination method with the reaction Cl + C2H6 as the refe
- Niki, H.,Maker. P. D.,Savage, C. M.,Breitenbach, L. P.
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- Cu single-atoms embedded in porous carbon nitride for selective oxidation of methane to oxygenates
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Cu single atoms embedded in the C3N4 (Cu-SAs/C3N4) matrix exhibited high activity with 95% oxygenate selectivity for the direct conversion of methane at ambient temperature. The presence of abundant anchoring sites in C3N4 led to highly dispersed Cu-N4 mo
- Wu, Bo,Yang, Ruoou,Shi, Lei,Lin, Tiejun,Yu, Xing,Huang, Min,Gong, Kun,Sun, Fanfei,Jiang, Zheng,Li, Shenggang,Zhong, Liangshu,Sun, Yuhan
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- High-Pressure Falloff Curves and Specific Rate Constants for the Reaction CH3 + O2 CH3O2 CH3O + O
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The recombination reaction CH3 + O2 -> CH3O2 was studied at room temperature by laser flash photolysis over the pressure range 0.25-150 bar in the bath gases Ar and N2.Falloff curves are onstructed, leading to a limiting high-pressure rate constant of krec,infinite = (2.2 +/- 0.3) E-12 cm3 molecule-1s-1.By use of a simplified adiabatic channel model, on the basis of the measured krec,infinite a set of specific rate constants k(E,J) is calculated for the unimolecular dissociation CH3O2 -> CH3 + O2 and compared with the reaction CH3O2 -> CH3O + O.With the derived specific rate constants, thermal rate constants for the reaction CH3 + O2 ->/- CH 3O + O are calculated and compared with experiments.
- Cobos, C. J.,Hippler, H.,Luther, K.,Ravishankara, A. R.,Troe, J.
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- Flash Photolysis Study of the CH3O2 + HO2 Reaction between 248 to 573 K
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The kinetics of the reaction CH3O2 + HO2 -> products (1) has been investigated between 248 and 573 K, using the flash photolysis-UV absorption technique.The rate constant, k1, was found to be independent of the presence of up to 12.8 Torr of wa
- Lightfoot, P. D.,Veyret, B.,Lesclaux, R.
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- Oxidation of a Monomethylpalladium(II) Complex with O2 in Water: Tuning Reaction Selectivity to Form Ethane, Methanol, or Methylhydroperoxide
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Photochemical aerobic oxidation of n-Pr4N[(dpms)PdIIMe(OH)] (5) and (dpms)PdIIMe(OH2) (8) (dpms = di(2-pyridyl)methanesulfonate) in water in the pH range of 6-14 at 21 °C was studied and found to produce, in combined high yield, a mixture of MeOH, C2H6, and MeOOH along with water-soluble n-Pr4N[(dpms)PdII(OH)2] (9). By changing the reaction pH and concentration of the substrate, the oxidation reaction can be directed toward selective production of ethane (up to 94% selectivity) or methanol (up to 54% selective); the yield of MeOOH can be varied in the range of 0-40%. The source of ethane was found to be an unstable dimethyl PdIV complex (dpms)PdIVMe2(OH) (7), which could be generated from 5 and MeI. For shedding light on the role of MeOOH in the aerobic reaction, oxidation of 5 and 8 with a range of hydroperoxo compounds, including MeOOH, t-BuOOH, and H2O2, was carried out. The proposed mechanism of aerobic oxidation of 5 or 8 involves predominant direct reaction of excited methylpalladium(II) species with O2 to produce a highly electrophilic monomethyl PdIV transient that is involved in subsequent transfer of its methyl group to 5 or 8, H2O, and other nucleophilic components of the reaction mixture.
- Sberegaeva, Anna V.,Zavalij, Peter Y.,Vedernikov, Andrei N.
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- Experimental confirmation of the low-temperature oxidation scheme of alkanes
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(Chemical equation presented) Intermediate detected: The design of internal combustion engines relies on a good understanding of the mechanism of the auto-ignition of hydrocarbons. A key assumption of this mechanism, which was commonly accepted but never proven, has now been experimentally demonstrated: the formation of ketohydroperoxides has been observed under conditions close to those actually observed before the auto-ignition.
- Battin-Leclerc, Frederique,Herbinet, Olivier,Glaude, Pierre-Alexandre,Fournet, Rene,Zhou, Zhongyue,Deng, Liulin,Guo, Huijun,Xie, Mingfeng,Qi, Fei
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- Oxygenation of methane with atmospheric oxygen in aqueous solution promoted by H2O2 and catalyzed by a vanadate ion-pyrazine-2-carboxylic acid system
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Methane is oxidized in aqueous solution with atmospheric oxygen and hydrogen peroxide in a reaction catalyzed by a NaVO3 - pyrazine-2-carboxylic acid system. Methyl hydroperoxide is selectively formed at 50°C. The turnover number of the catalyst after 24 h amounts to 480, and the yield of methyl hydroperoxide is 24% with respect to H2O2. Formaldehyde and formic acid are mainly formed at 120°C.
- Suess-Fink,Yan', Hong,Nizova,Stanislas,Shul'pin
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- FTIR product study of the reactions CH3O2 + CH3O2 and CH3O2 + O3
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The products of the self-reaction of methylperoxy radicals have been determined at 296 K in a 140-L chamber using continuous ultraviolet photolysis with FTIR detection. The branching fraction for the reaction channel giving methoxy radicals is found to be (41 ± 4)%, in good agreement with two earlier studies but somewhat higher than the most recent investigations. No evidence was found for the production of CH3OOCH3 (yield 3O2 with O3 occurring with a rate coefficient of 1 × 10-17 cm3 molecule-1 s-1, with an uncertainty of a factor of 2. As part of the present work a relative rate technique was used to measure k(Cl + CH3N2CH3) = (4.8 ± 0.6) × 10-11 cm3 molecule-1 s-1 at 296 K. The decay of peroxy radical concentrations in the nighttime clean troposphere is interpreted in terms of the product branching ratios and the rate coefficient for the reaction of CH3O2 + O3.
- Tyndall,Wallington,Ball
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- Unprecedentedly high efficiency for photocatalytic conversion of methane to methanol over Au-Pd/TiO2-what is the role of each component in the system?
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Direct and highly efficient conversion of methane to methanol under mild conditions still remains a great challenge. Here, we report that Au-Pd/TiO2 could directly catalyze the conversion of methane to methanol with an unprecedentedly high methanol yield of 12.6 mmol gcat-1 in a one-hour photocatalytic reaction in the presence of oxygen and water. Such an impressive efficiency is contributed by several factors, including the affinity between Au-Pd nanoparticles and intermediate species, the photothermal effect induced by visible light absorption of Au-Pd nanoparticles, the employment of O2 as a mild oxidant, and the effective dissolution of methanol in water. More importantly, for the first time, thermo-photo catalysis is demonstrated by the distinct roles of light. Namely, UV light is absorbed by TiO2 to excite charge carriers, while visible light is absorbed by Au-Pd nanoparticles to increase the temperature of the catalyst, which further enhances the driving force of corresponding redox reactions. These results not only provide a valuable guide for designing a photocatalytic system to realize highly efficient production of methanol, but also, highlight the great promise of thermo-photo catalysis. This journal is
- Cai, Xiaojiao,Fang, Siyuan,Hu, Yun Hang
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- A Supported Nickel Catalyst Stabilized by a Surface Digging Effect for Efficient Methane Oxidation
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A surface digging effect of supported Ni NPs on an amorphous N-doped carbon is described, during which the surface-loaded Ni NPs would etch and sink into the underneath carbon support to prevent sintering. This process is driven by the strong coordination interaction between the surface Ni atoms and N-rich defects. In the aim of activation of C?H bonds for methane oxidation, those sinking Ni NPs could be further transformed into thermodynamically stable and active metal-defect sites within the as-generated surface holes by simply elevating the temperature. In situ transmission electron microscopy images reveal the sunk Ni NPs dig themselves adaptive surface holes, which would largely prevent the migration of Ni NPs without weakening their accessibility. The reported two-step strategy opens up a new route to manufacture sintering-resistant supported metal catalysts without degrading their catalytic efficiency.
- Zhou, Huang,Liu, Tianyang,Zhao, Xuyan,Zhao, Yafei,Lv, Hongwei,Fang, Shi,Wang, Xiaoqian,Zhou, Fangyao,Xu, Qian,Xu, Jie,Xiong, Can,Xue, Zhenggang,Wang, Kai,Cheong, Weng-Chon,Xi, Wei,Gu, Lin,Yao, Tao,Wei, Shiqiang,Hong, Xun,Luo, Jun,Li, Yafei,Wu, Yuen
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- Reactive Channels of the CH3O2-CH3O2 Reaction
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Kinetic studies of the products of the CH3O2-CH3O2 reactions have been made by using long-path FT-IR spectroscopy.These allow an evaluation of the relative importance of the four suggested channels: 2CH3O2 -> 2CH3O + O2 (1a); 2CH3O2 -> CH2O + CH3OH + O2 (
- Kan, Charles S.,Calvert, Jack G.,Shaw, John H.
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- Low-temperature direct conversion of methane to methanol over carbon materials supported Pd-Au nanoparticles
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Direct conversion of methane to methanol under mild conditions remains a great challenge. Here, we report a class of carbon material catalysts for this direct synthesis. The carbon materials such as carbon nanotubes (CNTs), activated carbon (AC), and reduced graphene oxide (rGO) are employed as catalyst support, and the palladium-gold (Pd-Au) nanoparticles are used as active center. By using oxygen/hydrogen as oxidant in the direct synthesis, the catalyst of Pd-Au/CNTs shows outstanding methanol productivity and selectivity. Compared with the Pd-Au/CNTs, the Pd-Au/CNTs-n with a treatment of nitric acid for the support enhances the methanol selectivity, but decreases the methanol productivity. In addition, our characterization results reveal that a weak interaction between Pd-Au nanoparticles and CNTs support is in favor of methanol productivity and selectivity. In contrast, a strong interaction between Pd-Au and AC or rGO catalysts inhibits the reaction activity. This work offers a simple and effective strategy to directly synthesize methanol from methane under the mild conditions.
- He, Yingluo,Luan, Chunhui,Fang, Yuan,Feng, Xiaobo,Peng, Xiaobo,Yang, Guohui,Tsubaki, Noritatsu
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- Binary Au–Cu Reaction Sites Decorated ZnO for Selective Methane Oxidation to C1 Oxygenates with Nearly 100% Selectivity at Room Temperature
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Direct and efficient oxidation of methane to methanol and the related liquid oxygenates provides a promising pathway for sustainable chemical industry, while still remaining an ongoing challenge owing to the dilemma between methane activation and overoxidation. Here, ZnO with highly dispersed dual Au and Cu species as cocatalysts enables efficient and selective photocatalytic conversion of methane to methanol and one-carbon (C1) oxygenates using O2 as the oxidant operated at ambient temperature. The optimized AuCu–ZnO photocatalyst achieves up to 11225 μmol·g–1·h–1 of primary products (CH3OH and CH3OOH) and HCHO with a nearly 100% selectivity, resulting in a 14.1% apparent quantum yield at 365 nm, much higher than the previous best photocatalysts reported for methane conversion to oxygenates. In situ EPR and XPS disclose that Cu species serve as photoinduced electron mediators to promote O2 activation to ?OOH, and simultaneously that Au is an efficient hole acceptor to enhance H2O oxidation to ?OH, thus synergistically promoting charge separation and methane transformation. This work highlights the significances of co-modification with suitable dual cocatalysts on simultaneous regulation of activity and selectivity.
- Gong, Zhuyu,Liu, Huifen,Luo, Lei,Ma, Jiani,Tang, Junwang,Xing, Jialiang,Xu, Youxun
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supporting information
p. 740 - 750
(2022/01/03)
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- Lanthanum modified Fe-ZSM-5 zeolites for selective methane oxidation with H2O2
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Selective partial oxidation of methane to methanol under ambient conditions is a great challenge in chemistry. Iron modified ZSM-5 catalysts are shown to be effective for this reaction using H2O2as the oxidant. However, the high consumption of H2O2over this catalyst presents a major disadvantage. Here we report a lanthanum modified Fe-ZSM-5 (LaFe-ZSM-5) catalyst for enhanced selective methane oxidation with suppressed H2O2consumption. Using 0.5 wt% LaFe-ZSM-5 pretreated with H2the productivity of primary oxygenated products (CH3OH, CH3OOH, HCOOH) is 3200 mol kgLaFe?1h?1in 0.1 M H2O2, with a selectivity of 98.9% to primary oxygenated products. The productivity is increased to 11?460 mol kgLaFe?1h?1in 0.5 M H2O2. Compared with Fe-ZSM-5, LaFe-ZSM-5 uses 31% less H2O2for obtaining per mol of product under the same conditions.In situDRIFT spectroscopy and solid state MAS NMR revealed the high H2O2consumption in ZSM-5 based catalyst maybe closely related to the acidity of strong Br?nsted acid sites (Si(OH)Al). The La modified ZSM-5 catalyst can decrease the acidity of the strong Br?nsted acid sites and this suppresses the decomposition of H2O2
- Barnes, Alexandra J.,Bere, Takudzwa,Dummer, Nicholas F.,Gong, Xiaoxiao,Hutchings, Graham J.,Lewis, Richard J.,Morgan, David J.,Richards, Nia,Shaw, Greg,Sun, Songmei
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p. 8052 - 8064
(2021/12/27)
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- Oxidation of methane to methanol over Pd@Pt nanoparticles under mild conditions in water
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Direct methane oxidation into oxygen-containing chemicals under mild conditions has sparked increasing interest. Here, we report Pd@Pt core-shell nanoparticles that efficiently catalyse the direct oxidation of CH4to CH3OH in water using H2O2as an oxidant under mild conditions. The catalyst presents a methanol productivity of up to 89.3 mol kgcatalyst?1h?1with a high selectivity of 92.4% after 30 min at 50 °C, thus outperforming most of the previously reported catalysts. Electron-enriched Pt species in the Pd@Pt nanoparticles were identified by structural and electronic analysis. Pd in the core donates electrons to Pt, leading to higher rates of methane activation. Based on the results of control experiments and kinetic analysis, a consecutive oxidation pathwayviaa radical mechanism is proposed, which includes initial formation of CH3OOH and CH3OH followed by further oxidation of CH3OH to HCHO, HCOOH, and CO2
- Chen, Jianjun,Chen, Yaoqiang,Collière, Vincent,Lecante, Pierre,Peres, Laurent,Philippot, Karine,Wang, Sikai,Yan, Ning
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p. 3493 - 3500
(2021/06/06)
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- Efficient Synthesis of Monomeric Fe Species in Zeolite ZSM-5 for the Low-Temperature Oxidation of Methane
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Direct oxidation of methane into value-added C1 oxygenated products, such as methanol, is essential and remains a significant challenge in the field of catalysis. In this work, we have prepared Fe/ZSM-5 materials via three different methods and investigated the influence of various preparation methods on the composition and catalytic performance of Fe/ZSM-5 for the low-temperature oxidation of methane. Through a combination of scanning transmission electron microscopy, ultraviolet-visible diffuse reflectance and 57Fe M?ssbauer spectroscopy, we have found that the highest proportion of monomeric Fe species of 71 % could be achieved in the ZSM-5 zeolite by the solid-state ion-exchange method, affording an excellent C1 oxygenates yield of 120 mol/molFe with a C1 oxygenates selectivity of 96 % at 50 °C for 30 min in the aqueous solution of H2O2.
- Yu, Tao,Su, Yang,Wang, Aiqin,Weckhuysen, Bert M.,Luo, Wenhao
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p. 2766 - 2770
(2021/05/07)
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- Low temperature selective oxidation of methane using gold-palladium colloids
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Methane upgrading into energy-dense liquid derivatives (such as methanol or mid-range hydrocarbons) is a highly desirable process to increase its utilisation. The selective oxidation of methane using hydrogen peroxide has been investigated using unsupported gold-palladium nanoparticles prepared using colloidal methods. The effect of the reaction conditions and the catalyst parameters have been systematically investigated. Poly(vinyl)pyrrolidone (PVP) stabilised Au-Pd colloids produce methyl hydroperoxide as the primary reaction product, which is subsequently converted to methanol with high oxygenate selectivity. The stability and re-use characteristics of the colloidal catalyst have also been assessed for methane oxidation with hydrogen peroxide.
- McVicker, Rebecca,Agarwal, Nishtha,Freakley, Simon J.,He, Qian,Althahban, Sultan,Taylor, Stuart H.,Kiely, Christopher. J.,Hutchings, Graham J.
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- Gold-palladium colloids as catalysts for hydrogen peroxide synthesis, degradation and methane oxidation: Effect of the PVP stabiliser
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The reactivity of AuPd nanoparticle catalysts prepared by sol immobilisation is often explained by a structure activity relationship based solely on particle size or composition. In this contribution, we compare colloidal AuPd nanoparticles stabilised with polyvinylpyrrolidone (PVP) with the same AuPd nanoparticles supported on TiO2 for the direct synthesis of hydrogen peroxide and methane oxidation to methanol. We show that while the particles have similar rates of H2O2 synthesis, supporting the particles can affect the rates of H2O2 decomposition and hence the effectiveness of the catalyst for reactions which rely on H2O2 as an initiator or oxidant. We demonstrate that the absence of PVP results in high rates of H2O2 decomposition in methane oxidation experiments but this can be minimised by the addition of PVP to the reactor. These results also show that for AuPd alloys, both polymer stabiliser and support effects need to be taken into account when describing the activity of the nanoparticles and the active sites should in fact be thought of as a metal-support-polymer interface with many degrees of freedom. This journal is
- Agarwal, Nishtha,Althahban, Sultan,Dimitratos, Nikolaos,Freakley, Simon J.,Hutchings, Graham J.,Kiely, Christopher J.,Lewis, Richard J.,McVicker, Rebecca U.,Morgan, David J.
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p. 5935 - 5944
(2020/10/08)
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- Highly selective aerobic oxidation of methane to methanol over gold decorated zinc oxide: Via photocatalysis
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Photodriven CH4 conversion has been regarded as a promising green strategy for fabrication of value-added commodity chemicals, in particular methanol. However, due to the incomplete transformation of intermediates or the overoxidation of products, a good selectivity of methanol is hard to achieve. Here, we present a highly selective transformation of methane to methanol using gold modified zinc oxide as a photocatalyst under full light spectrum irradiation at atmospheric temperature. The selectivity of methanol can reach 99.1percent with a productivity of 1371 μmol g-1. Fine tuning the loading amount of gold nanoparticles (0.75 wtpercent) and inputting an appropriate light energy are the pivotal factors for selectivity improvement. Besides, in contrast to the reported photocatalytic aerobic CH4 oxidation on gold modified zinc oxide, we find that both oxygen and water, rather than only molecular oxygen, provide the O-source for methanol formation. This result is verified through 18O-isotope tests (18O2 and H218O), leading to a disparate mechanism.
- Fan, Yingying,Han, Dongxue,Jiang, Yuheng,Niu, Li,Qiu, Xueying,Tang, Zhiyong,Wei, Shilei,Zhou, Wencai
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supporting information
p. 13277 - 13284
(2020/07/16)
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- Room temperature and atmospheric pressure aqueous partial oxidation of ethane to oxygenates over AuPd catalysts
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New modes of chemical manufacturing based on small-scale, distributed facilities have been proposed to supplement many existing production operations in the chemical industry, including the synthesis of value-added products from light alkanes. Motivated by this prospect, herein the aqueous partial oxidation of ethane over unsupported AuPd nanoparticle catalysts is investigated, with emphasis on outcomes for reactions occurring at 21 °C and 1 bar ethane. When H2O2 is used as an oxidant, the system generates numerous C2 oxygenates, including ethyl hydroperoxide/ethanol, acetaldehyde, and acetic acid. Ethyl hydroperoxide is found to be the primary product resulting from the direct oxidation of ethane: it is produced with 100% selectivity in batch reactions with short durations and with low initial H2O2 concentrations. At longer times or in more oxidizing conditions, deeper product oxidations expectedly occur. In batch experiments, the maximum observed yield of oxygenates is 7707 μmol gAuPd-1 h-1. Product distributions differ when H2O2 is replaced by H2 and O2 in the headspace. Additionally, to simulate a scenario wherein H2O2 is produced on-site and to study ethane oxidation in steady, low H2O2 concentrations over 50 h, a semi-batch configuration facilitating continuous injection of dilute H2O2 was implemented. These efforts showed that H2O2 can serve as an oxygenate-selective oxidant of ethane when its concentration is kept low during reaction. These and other experimental results, as well as initial computational results using density functional theory, suggest that paths forward for aqueous ethane conversion exist, and systems should be engineered to emphasize product stabilization.
- Felvey, Noah,Gurses, Sadi,Kronawitter, Coleman X.,Wang, Yu Lei
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p. 6679 - 6686
(2020/11/16)
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- Single Chromium Atoms Supported on Titanium Dioxide Nanoparticles for Synergic Catalytic Methane Conversion under Mild Conditions
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Direct conversion of methane to value-added chemicals with high selectivity under mild conditions remains a great challenge in catalysis. Now, single chromium atoms supported on titanium dioxide nanoparticles are reported as an efficient heterogeneous catalyst for direct methane oxidation to C1 oxygenated products with H2O2 as oxidant under mild conditions. The highest yield for C1 oxygenated products can be reached as 57.9 mol molCr?1 with selectivity of around 93 % at 50 °C for 20 h, which is significantly higher than those of most reported catalysts. The superior catalytic performance can be attributed to the synergistic effect between single Cr atoms and TiO2 support. Combining catalytic kinetics, electron paramagnetic resonance, and control experiment results, the methane conversion mechanism was proposed as a methyl radical pathway to form CH3OH and CH3OOH first, and then the generated CH3OH is further oxidized to HOCH2OOH and HCOOH.
- Shen, Qikai,Cao, Changyan,Huang, Runkun,Zhu, Lei,Zhou, Xin,Zhang, Qinghua,Gu, Lin,Song, Weiguo
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supporting information
p. 1216 - 1219
(2019/12/12)
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- Activating and Converting CH4 to CH3OH via the CuPdO2/CuO Nanointerface
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The activation and conversion of methane (CH4) is one of the most challenging processes, because of the high chemical inertness of CH4 and the subsequent uncontrollable overoxidation. Herein, we report that the CuPdO2/CuO interface in PdxCu1-xO/C can efficiently activate and convert CH4 to CH3OH using H2O2 or O2 as the oxidant under mild conditions, where the CH3OH yield (4076.5 μmol g-1) and selectivity (93.9%) of the optimized Pd0.3Cu0.7O/C are much higher than those of PdO/C, CuPdO2/C, and the mixture of CuPdO2/C and CuO/C. Structural characterizations and mechanism studies reveal that the highly activity of Pd0.3Cu0.7O/C is attributed to the strong synergistic effects in PdxCu1-xO/C. The formation of Pd4+ species at the interfaces of CuPdO2 and CuO, which is promoted by the electron transfer from Cu to Pd, can selectively oxidize CH4 to produce CH3OH. This work highlights the importance of controlled interface in Pd-based catalysts for heterogeneous catalysis and beyond.
- Bai, Shuxing,Xu, Yong,Wang, Pengtang,Shao, Qi,Huang, Xiaoqing
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p. 6938 - 6944
(2019/08/28)
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- Aqueous-Phase Selective Oxidation of Methane with Oxygen over Iron Salts and Pd/C in the Presence of Hydrogen
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Direct conversion of methane into value-added chemicals is a challenging but worthwhile subject. In this communication, the direct conversion of methane into methane oxygenates was achieved in an aqueous solution at room temperature using iron salts and Pd/C as catalysts and hydrogen peroxide as an oxidant. The hydrogen peroxide can be directly added or generated in situ from hydrogen and oxygen. The Pd/C catalyst greatly enhanced the reaction rate together with the iron salts. The effect of some parameters such as reaction temperature, reaction time, pH, acid type, and catalyst amount on the yields of the methane oxygenates was also investigated. When hydrogen peroxide was directly added, the turnover frequency (TOF), defined as the moles of methane oxygenates per moles of Fe per unit time, at 293 K was 29 h?1 at pH=2.3. The TOF at 293 K was 42 h?1 at pH=1.3 with in situ generated hydrogen peroxide from hydrogen and oxygen.
- Kang, Jongkyu,Park, Eun Duck
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p. 4247 - 4251
(2019/08/07)
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- Room-Temperature Methane Conversion by Graphene-Confined Single Iron Atoms
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Direct conversion of methane to high-value-added chemicals is a major challenge in catalysis, which usually requires high-energy input to overcome the reaction barrier. We report that graphene-confined single Fe atoms can be used as an efficient non-precious catalyst to directly convert methane to C1 oxygenated products at room temperature. A series of graphene-confined 3d transition metals (Mn, Fe, Co, Ni, and Cu) were screened, yet only single Fe atoms could catalyze the methane conversion. Combining in operando time-of-flight mass spectrometry, 13C nuclear magnetic resonance, and density functional theory calculations, we found that methane conversion proceeds on the O–FeN4–O active site along a radical pathway to produce CH3OH and CH3OOH first, and then the generated CH3OH can be further catalyzed to form HOCH2OOH and HCOOH at room temperature. Methane from natural gas and shale gas is one of the most promising feedstocks because of its high reserves and low price. The selective activation and orientable conversion of methane are considered the “holy grail” in catalysis. Because of the highly stable C–H bond, methane conversion usually requires high temperatures to overcome the high reaction barrier. However, the high-temperature reaction is not favorable for industrial application. Despite many efforts to decrease the reaction temperature, it remains a great challenge to promote methane conversion under mild conditions, especially at room temperature. Herein, we report that graphene-confined single Fe atoms can be used as an efficient non-precious catalyst to directly convert methane to high-value-added C1 oxygenated products at room temperature (25°C), which provides a new route to understanding and designing highly efficient non-precious catalysts for methane conversion at room temperature. Graphene-confined single Fe atoms, screened out from a series of 3d transition metals (Mn, Fe, Co, Ni, and Cu), were used as an efficient non-precious catalyst to directly convert methane to C1 oxygenated products at room temperature. The unique O–FeN4–O structure formed in graphene can readily activate the C–H bond of methane along a radical pathway with a low reaction energy barrier.
- Cui, Xiaoju,Li, Haobo,Wang, Yan,Hu, Yuanli,Hua, Lei,Li, Haiyang,Han, Xiuwen,Liu, Qingfei,Yang, Fan,He, Limin,Chen, Xiaoqi,Li, Qingyun,Xiao, Jianping,Deng, Dehui,Bao, Xinhe
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supporting information
p. 1902 - 1910
(2018/06/20)
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- The Role of Copper Speciation in the Low Temperature Oxidative Upgrading of Short Chain Alkanes over Cu/ZSM-5 Catalysts
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Partial oxidative upgrading of C1–C3 alkanes over Cu/ZSM-5 catalysts prepared by chemical vapour impregnation (CVI) has been studied. The undoped ZSM-5 support is itself able to catalyse selective oxidations, for example, methane to methanol, using mild reaction conditions and the green oxidant H2O2. Addition of Cu suppresses secondary oxidation reactions, affording methanol selectivities of up to 97 %. Characterisation studies attribute this ability to population of specific Cu sites below the level of total exchange (Cu/Al0.5). These species also show activity for radical-based methane oxidation, with productivities exceeding those of the parent zeolite supports. When tested for ethane and propane oxidation reactions, comparable trends are observed.
- Armstrong, Robert D.,Peneau, Virginie,Ritterskamp, Nadine,Kiely, Christopher J.,Taylor, Stuart H.,Hutchings, Graham J.
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p. 469 - 478
(2018/01/27)
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- Selective Oxidation of Methane to Methanol Using Supported AuPd Catalysts Prepared by Stabilizer-Free Sol-Immobilization
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The selective oxidation of methane to methanol, using H2O2, under mild reaction conditions was studied using bimetallic 1 wt % AuPd/TiO2 prepared by stabilizer-free sol-immobilization. The as-prepared catalysts exhibited low, unselective oxidation activity and deleterious H2O2 decomposition, which was ascribed to the small mean particle size of the supported AuPd nanoparticles. Heat treatments were employed to facilitate particle size growth, yielding an improvement in the catalyst turnover frequency and decreasing the H2O2 decomposition rate. The effect of support phase was studied by preparing a range of AuPd catalysts supported on rutile TiO2. The low surface area rutile TiO2 yielded catalysts with effective oxygenate production but poor H2O2 utilization. The influence of the rutile-TiO2 support was investigated further by producing catalysts with a lower metal loading to maintain a consistent metal loading per square meter compared to the 1 wt % AuPd/P25 TiO2 catalyst. When calcined at 800 °C, the 0.13 wt % AuPd catalyst demonstrated significantly improved turnover frequency of 103 h-1. In contrast, the turnover frequency was found to be ca. 2 h-1 for the rutile-supported 1 wt % AuPd catalyst calcined at 800 °C. The catalysts were probed by electron microscopy and X-ray photoelectron spectroscopy to understand the influence of particle size and oxidation state on the utilization of H2O2 and oxygenate productivity. This work shows that the key to highly active catalysts involves the prevention of deleterious H2O2 decomposition, and this can be achieved through carefully controlling the nanoparticle size, metal loading, and metal oxidation state.
- Williams, Christopher,Carter, James H.,Dummer, Nicholas F.,Chow, Y. Kit,Morgan, David J.,Yacob, Sara,Serna, Pedro,Willock, David J.,Meyer, Randall J.,Taylor, Stuart H.,Hutchings, Graham J.
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p. 2567 - 2576
(2018/03/13)
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- HYDROCARBON OXIDATION
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A method of direct oxidation of a hydrocarbon to produce an oxygenated reaction product, wherein said method comprises contacting a peroxide and oxygen and the hydrocarbon with a suspension of catalyst particles dispersed in a liquid reaction medium, wherein the catalyst particles are unsupported and comprise at least one transition metal.
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Page/Page column 10-11; 14; 15
(2018/12/03)
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- Low temperature selective oxidation of methane to methanol using titania supported gold palladium copper catalysts
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The selective oxidation of methane to methanol has been studied using trimetallic AuPdCu/TiO2 catalysts prepared by incipient wetness impregnation. They are able to catalyse the selective oxidation of methane to methanol under mild aqueous reaction conditions using H2O2 as the oxidant. When compared with bimetallic, Au-Pd/TiO2 analogues, the new trimetallic catalysts present productivities which are up to 5 times greater under the same test conditions, and this is coupled with methanol selectivity of up to 83%. Characterisation shows that whilst Au-Pd is present as Au-core-Pd-shell nanoparticles, copper is present as either Cu or Cu2O in 5 nm particles.
- Ab Rahim, Mohd Hasbi,Armstrong, Robert D.,Hammond, Ceri,Dimitratos, Nikolaos,Freakley, Simon J.,Forde, Michael M.,Morgan, David J.,Lalev, Georgi,Jenkins, Robert L.,Lopez-Sanchez, Jose Antonio,Taylor, Stuart H.,Hutchings, Graham J.
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p. 3410 - 3418
(2016/06/09)
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- Aqueous-phase methane oxidation over Fe-MFI zeolites; Promotion through isomorphous framework substitution
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Fe- and Cu-containing zeolites have recently been shown to be efficient catalysts for the one-step selective transformation of methane into methanol in an aqueous medium at only 50 C, using H2O2 as green oxidant. Previously, we have observed that Fe species alone are capable of catalyzing this highly selective transformation. However, further catalytic testing and spectroscopic investigations demonstrate that although these extra-framework Fe species are the active component of the catalyst, significant promotion is observed upon the incorporation of other trivalent cations, e.g., Al3+ or Ga3+, into the MFI-framework. While these additional framework species do not constitute active catalytic centers, promotion is observed upon their incorporation as they (1) facilitate the extraction of Fe from the zeolite framework and hence increase the formation of the active Fe species and (2) provide an associated negatively charged framework, which is capable of stabilizing and maintaining the dispersion of the cationic extra-framework Fe species responsible for catalytic activity. By understanding these phenomena and subsequently controlling the overall composition of the catalyst (Fe and Al), we have subsequently been able to prepare a catalyst of equal intrinsic activity (i.e., TOF) but five-times higher productivity (i.e., space-time-yield) compared with the best catalysts reported for this reaction to date.
- Hammond, Ceri,Dimitratos, Nikolaos,Lopez-Sanchez, Jose Antonio,Jenkins, Robert L.,Whiting, Gareth,Kondrat, Simon A.,Ab Rahim, Mohd Hasbi,Forde, Michael M.,Thetford, Adam,Hagen, Henk,Stangland, Eric E.,Moulijn, Jacob M.,Taylor, Stuart H.,Willock, David J.,Hutchings, Graham J.
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p. 1835 - 1844
(2013/09/02)
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- SELECTIVE HYDROCARBON OXIDATION USING HETEROGENOUS CATALYSTS
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A process for the complete or partial oxidation of hydrocarbons comprises contacting a C1-C8 hydrocarbon and hydrogen peroxide in the presence of a heterogeneous catalyst under conditions suitable to convert the C1-C8 hydrocarbon to at least one corresponding C1-C8 oxygenate product, wherein the heterogeneous catalyst provides confinement and contains both Br?nsted-Lowry and Lewis acid centers. Particularly useful catalysts may include, for example, metal-modified ZSM-5 and other zeolites.
- -
-
Paragraph 0038
(2013/04/13)
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- SELECTIVE OXYGENATION OF ALKANES USING OXYGEN
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A process for the complete or partial oxygenation of hydrocarbons comprises contacting a C1-C8 hydrocarbon, molecular oxygen, and hydrogen peroxide, in the presence of water and a heterogeneous catalyst, under conditions suitable to convert the C1-C8 hydrocarbon to at least one corresponding C1-C8 oxygenate product, wherein the heterogeneous catalyst provides confinement and contains both Br?nsted-Lowry acid centers and Lewis acid centers. The reaction may be carried out at a temperature ranging from 2°C to 90°C. The use of molecular oxygen increases the economic attractiveness of the process while also improving yield.
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Page/Page column 10-12
(2013/05/09)
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- Partial oxidation of ethane to oxygenates using Fe- and Cu-containing ZSM-5
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Iron and copper containing ZSM-5 catalysts are effective for the partial oxidation of ethane with hydrogen peroxide giving combined oxygenate selectivities and productivities of up to 95.2% and 65 mol kgcat -1 h-1, respectively. High conversion of ethane (ca. 56%) to acetic acid (ca. 70% selectivity) can be observed. Detailed studies of this catalytic system reveal a complex reaction network in which the oxidation of ethane gives a range of C2 oxygenates, with sequential C-C bond cleavage generating C1 products. We demonstrate that ethene is also formed and can be subsequently oxidized. Ethanol can be directly produced from ethane, and does not originate from the decomposition of its corresponding alkylperoxy species, ethyl hydroperoxide. In contrast to our previously proposed mechanism for methane oxidation over similar zeolite catalysts, the mechanism of ethane oxidation involves carbon-based radicals, which lead to the high conversions we observe.
- Forde, Michael M.,Armstrong, Robert D.,Hammond, Ceri,He, Qian,Jenkins, Robert L.,Kondrat, Simon A.,Dimitratos, Nikolaos,Lopez-Sanchez, Jose Antonio,Taylor, Stuart H.,Willock, David,Kiely, Christopher J.,Hutchings, Graham John
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supporting information
p. 11087 - 11099
(2013/08/23)
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- HYDROCARBONS SELECTIVE OXIDATION WITH HETEROGENEOUS CATALYSTS
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A process for the complete or partial oxidation of hydrocarbons comprises contacting a C1-C8 hydrocarbon and hydrogen peroxide in the presence of a heterogeneous catalyst under conditions suitable to convert the C1-C8 hydrocarbon to at least one corresponding C1-C8 oxygenate product, wherein the heterogeneous catalyst provides confinement and contains both Br?nsted-Lowry and Lewis acid centers. Examples include zeolites modified with selected metals or metal oxides. Including copper, either in the catalyst, in a second catalyst of similar description, or as a homogeneous salt, increases both selectivity and activity of the process, particularly where an iron-containing catalyst is used.
- -
-
Paragraph 0042
(2014/01/07)
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- Oxidation of methane to methanol with hydrogen peroxide using supported gold-palladium alloy nanoparticles
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Direct and selective: Supported gold-palladium nanoparticles are active for the oxidation of methane, giving a high selectivity for the formation of methyl hydroperoxide and methanol, using hydrogen peroxide as the oxidant (see picture). The optimal methanol selectivity is achieved by performing the reaction in the presence of hydrogen peroxide that has been generated in situ from hydrogen and oxygen. Copyright
- Ab Rahim, Mohd Hasbi,Forde, Michael M.,Jenkins, Robert L.,Hammond, Ceri,He, Qian,Dimitratos, Nikolaos,Lopez-Sanchez, Jose Antonio,Carley, Albert F.,Taylor, Stuart H.,Willock, David J.,Murphy, Damien M.,Kiely, Christopher J.,Hutchings, Graham J.
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supporting information
p. 1280 - 1284
(2013/03/14)
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- Branching ratios for the reaction of selected carbonyl-containing peroxy radicals with hydroperoxy radicals
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An important chemical sink for organic peroxy radicals (RO2) in the troposphere is reaction with hydroperoxy radicals (HO2). Although this reaction is typically assumed to form hydroperoxides as the major products (R1a), acetyl peroxy radicals and acetonyl peroxy radicals have been shown to undergo other reactions (R1b) and (R1c) with substantial branching ratios: RO2 + HO2 → ROOH + O2 (R1a), RO 2 + HO2 → ROH + O3 (R1b), RO2 + HO2 → RO + OH + O2 (R1c). Theoretical work suggests that reactions (R1b) and (R1c) may be a general feature of acyl peroxy and α-carbonyl peroxy radicals. In this work, branching ratios for R1a-R1c were derived for six carbonyl-containing peroxy radicals: C2H 5C(O)O2, C3H7C(O)O2, CH3C(O)CH2O2, CH3C(O)CH(O 2)CH3, CH2ClCH(O2)C(O)CH 3, and CH2ClC(CH3)(O2)CHO. Branching ratios for reactions of Cl-atoms with butanal, butanone, methacrolein, and methyl vinyl ketone were also measured as a part of this work. Product yields were determined using a combination of long path Fourier transform infrared spectroscopy, high performance liquid chromatography with fluorescence detection, gas chromatography with flame ionization detection, and gas chromatography-mass spectrometry. The following branching ratios were determined: C2H5C(O)O2, YR1a = 0.35 ± 0.1, YR1b = 0.25 ± 0.1, and YR1c = 0.4 ± 0.1; C3H7C(O)O2, YR1a = 0.24 ± 0.15, YR1b = 0.29 ± 0.1, and YR1c = 0.47 ± 0.15; CH3C(O)CH2O2, Y R1a = 0.75 ± 0.13, YR1b = 0, and YR1c = 0.25 ± 0.13; CH3C(O)CH(O2)CH3, Y R1a = 0.42 ± 0.1, YR1b = 0, and YR1c = 0.58 ± 0.1; CH2ClC(CH3)(O2)CHO, Y R1a = 0.2 ± 0.2, YR1b = 0, and YR1c = 0.8 ± 0.2; and CH2ClCH(O2)C(O)CH3, YR1a = 0.2 ± 0.1, YR1b = 0, and YR1c = 0.8 ± 0.2. The results give insights into possible mechanisms for cycling of OH radicals in the atmosphere.
- Hasson, Alam S.,Tyndall, Geoffrey S.,Orlando, John J.,Singh, Sukhdeep,Hernandez, Samuel Q.,Campbell, Sean,Ibarra, Yesenia
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experimental part
p. 6264 - 6281
(2012/08/28)
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- Osmium-catalyzed selective oxidations of methane and ethane with hydrogen peroxide in aqueous medium
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Various transition metal chlorides including FeCl3, CoCl 2, RuCl3, RhCl3, PdCl2, OsCl 3, IrCl3, H2PtCl6, CuCl2 and HAuCl4 were studied for the selective oxidations of methane and ethane with hydrogen peroxide in aqueous medium. Among the metal chlorides investigated, osmium(III) chloride (OsCl3) exhibited the highest turnover frequency (TOF) for the formation of organic oxygenates (mainly alcohols and aldehydes) from both methane and ethane. For the OsCl 3-catalyzed oxidation of methane with hydrgen peroxide, methyl hydroperoxide was also formed together with methanol and formaldehyde. The effects of various kinetic factors on the catalytic behavior of the OsCl 3-H2O2 system were investigated, and TOF values of 12 and 41 h-1 could be obtained for oxygenate formation during the oxidations of methane and ethane, respectively. In the presence of OsCl 3, NaClO, NaClO4 or NaIO4 as oxidant was incapable of oxidizing methane and ethane to the corresponding oxygenates, and the use of tert-butyl hydroperoxide (TBHP) instead of H2O2 provided remarkably lower rates of formation of oxygenates. UV-Vis spectroscopic measurements suggested that OsCl3 was probably oxidized into an Os(IV) species by H2O2 in aqueous medium, and the Os(IV) species might be involved in the oxygenation of methane or ethane. The result that the conversions of both methane and ethane to oxygenates were suppressed by the addition of a radical scavenger suggested that the reactions proceeded via a radical pathway.
- Yuan, Qiang,Deng, Weiping,Zhang, Qinghong,Wang, Ye
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p. 1199 - 1209
(2008/04/03)
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- Hydroperoxidation of methane and other alkanes with H2O2 catalyzed by a dinuclear iron complex and an amino acid
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The compound [Fe2(HPTB)(μ-OH)(NO3)2](NO3) 2·CH3OH·2H2O (1) containing a dinuclear iron(III) complex in which HPTB=N,N,N′,N′-tetrakis(2-benzimidazolylmethyl)-2-hydroxo-1,3- diaminopropane catalyzes the oxidation of alkanes with hydrogen peroxide in acetonitrile solution at room temperature only if certain amino acids (pyrazine-2-carboxylic, pyrazine-2,3-dicarboxylic or picolinic acid) are added to the reaction mixture. Alkyl hydroperoxides are formed as main reaction products. The turnover numbers attain 140 for cyclohexane, 21 for ethane and four for methane oxidation. The oxidation proceeds non-stereoselectively and bond selectivity parameters are low which testifies the participation of hydroxyl radicals in alkane functionalization.
- Nizova, Galina V.,Krebs, Bernt,Süss-Fink, Georg,Schindler, Siegfried,Westerheide, Lars,Gonzalez Cuervo, Laura,Shul'pin, Georgiy B.
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p. 9231 - 9237
(2007/10/03)
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- Formation mechanism of peroxides in reactions of cyclic olefins with ozone in air
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We carried out reactions of methyl-substituted cyclohexenes and α-pinene with ozone in air and elucidated the mechanisms of formation of the minor products (peroxides and formic acid). Peroxyacetic acid was formed only from the cyclohexenes with a methyl group on the double bond, whereas formic acid was produced in higher yields from the cyclohexenes without a methyl group on the double bond. These differences in product yields allowed us to elucidate the mechanism of formation of the products.
- Hatakeyama, Shiro,Sivanesan, Subramanian,Urabe, Taichiro
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p. 1248 - 1249
(2007/10/03)
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- Oxidations by the system 'hydrogen peroxide-manganese(IV) complex- acetic acid' - Part II: Hydroperoxidation and hydroxylation of alkanes in acetonitrile
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Higher alkanes (cyclohexane, n-pentane, n-heptane, methylbutane, 2- and 3-methylpentanes, 3-methylhexane, cis- and trans-decalins) are oxidized at 20 °C by H2O2 in air in acetonitrile (or nitromethane) solution in the presence of the manganese(IV) salt [L2Mn2O3](PF6)2 (L = 1,4,7-trimethyl- 1,4-7-triazacyclononane) as the catalyst. An obligatory component of the reaction mixture is acetic acid. Turnover numbers attain 3300 after 2 h, the yield of oxygenated products is 46% based on the alkane. The oxidation affords initially the corresponding alkyl hydroperoxide as the predominant product, however later these compounds decompose to produce the corresponding ketones and alcohols. Regio- and bond selectivities of the reaction are high: C(1): C(2): C(3): C(4) ? 1: 40: 35: 35 and 1°: 2°: 3°is 1: (15-40): (180-300). The reaction with both isomers of decalin gives (after treatment with PPh3) alcohols hydroxylated in the tertiary positions with the cis/trans ratio of ~2 in the case of cis-decalin, and of ~30 in the case of trans-decalin (i.e. in the latter case the reaction is stereospecific). Light alkanes (methane, ethane, propane, normal butane and isobutane) can be also easily oxidized by the same reagent in acetonitrile solution, the conditions being very mild: low pressure (1-7 bar of the alkane) and low temperature (- 22 to +27°C). Catalyst turnover numbers attain 3100, the yield of oxygenated products is 22% based on the alkane. The yields of oxygenates are higher at low temperatures. The ratio of products formed (hydroperoxide: ketone: alcohol) depends very strongly on the conditions of the reaction and especially on the catalyst concentration (at higher catalyst concentration the ketone is predominantly produced).
- Shul'pin, Georgiy B.,Suess-Fink, Georg,Lindsay Smith, John R.
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p. 5345 - 5358
(2007/10/03)
-
- Identification of organic peroxides in the oxidation of C1-C3 alkanes
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Formation of organic peroxides in oxidation of C1-C3 alkanes initiated by C1 atoms in O2-N2 mixtures at 760 torr and 298 K was studied with FT-IR and HPLC method in laboratory. Methyl hydroperoxide (MHP) and ethyl hydroperoxide (EHP) were the main peroxide products and formed early in the oxidation process. Hydroxymethyl hydroperoxide (HOCH2OOH, HMHP) was identified in the reaction systems. Other two types of peroxides detected were peroxyacetic acid (CH3C(O)OOH, PAA) and dimethyl peroxide (C-H3OOCH3, DMP). In addition, more than seven peroxide products were not identified. The finding of HMHP in the system indicated that Criegee biradical CH2OO probably was an intermediate in the process of oxidation of alkanes. The results implied that oxidation of alkanes may have a significant contribution to organic peroxides in the troposphere.
- Qi,Zhang,Chen,Shao,Tang,Hu
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p. 1213 - 1221
(2007/10/03)
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- Oxidations by the reagent 'O2-H2O2-vanadium complex-pyrazine-2-carboxylic acid' - VIII. Efficient oxygenation of methane and other lower alkanes in acetonitrile
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Methane, ethane, propane, n-butane and isobutane can be readily oxidized in acetonitrile solution by air and H2O2 at 20-75°C using the catalytic system [n-Bu4N]VO3/pyrazine-2-carboxylic acid, Apart from alkyl hydroperoxides which are the primary oxidation products, more stable derivatives (alcohols, aldehydes or ketones and carboxylic acids) are obtained with high total turnover numbers (e.g., at 75°C after 4 h: 420 for methane and 2130 for ethane). It was shown in the case of ethane and cyclohexane that alkanes do not yield oxygenated products in the absence of air. The cyclohexane oxidation under an 18O2 atmosphere showed a high degree of 18O incorporation into the oxygenated products. Thus in the oxidation reaction described here H2O2 is only the promoter while O2 is the 'true' oxidant.
- Nizova, Galina V.,Suess-Fink, Georg,Shul'pin, Georgiy B.
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p. 3603 - 3614
(2007/10/03)
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- Pressure dependence of the rate coefficients and product yields for the reaction of CH3CO radicals with O2
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Relative rate coefficients for the reaction of acetyl (CH3CO) radicals with O2 (k4) and Cl2 (k7,) have been obtained at 298 K and 228 K as a function of total pressure, using FTIR/environmental chamber techniques. Measured values of k4/k7 were placed on an absolute basis using k7 = 2.8 × 10-11 exp(-47/T) cm3 molec-1 s-1. At 298 K, the value of k4 is constant ((7 ± 2) × 10-13 cm3 molec-1 s-1) at pressures from 0.1 to 2 torr, then increases to a high pressure limiting value of (3.2 ± 0.6) × 10-12 cm3 molec-1 s-1. which is approached at pressures above 300 torr. At 228 K, the low-pressure value of k4 increases by about 20-30% while the high pressure value remains unchanged. Experiments designed to elucidate the products of reaction (4) as a function of pressure at 298 K indicate that the reaction occurs via a concerted mechanism in which CH3CO radicals combine with O2 to give an excited acetylperoxy radical (CH3COO2*) which is increasingly stabilized at high pressure at the expense of a low pressure decomposition channel. The yield of acetylperoxy radicals from reaction (4) decreases from >95% at pressures above 100 torr, to about 90% at 60 torr, and 50% at 6 torr. Indirect evidence for formation of OH radicals from the low pressure decomposition is presented, although the carbon-containing coproduct(s) of this channel could not be identified.
- Tyndall, Geoffrey S.,Orlando, John J.,Wallington, Timothy J.,Hurley, Michael D.
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p. 655 - 663
(2007/10/03)
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- FTIR Kinetic and Mechanistic Study of the Atmospheric Chemistry of Methyl Thiolformate
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Some aspects of the atmospheric chemistry of methyl thiolformate (CH3SCHO), a recently detected intermediate in the oxidation of dimethyl sulfide, have been investigated at 298 K and 1000 mbar total pressure in large reaction chambers using long path in situ FTIR absorption spectroscopy for the analysis.Rate coefficients of (1.11 +/- 0.22)E-11 and (5.80 +/- 0.80)E-11 cm3 molecule-1 s-1 have been determined for its reaction with OH radicals and Cl atoms, respectively.The UV spectrum of CH3SCHO has been measured in the range 220-355 nm and a lower limit of 5.4 days determined for its atmospheric photolytic lifetime.Detailed product analyses have made for the OH and Cl initiated photooxidation of CH3SCHO.Strong SO absorption bands observed in both systems are tentatively assigned to CH3SOCHO in the OH system and to CH3SOCl in the Cl system.The first gas-phase spectra of CH3SCl and CH3SOCl are also presented.The results are discussed with respect to the atmospheric chemistry of CH3SCHO and possible consequences for the photooxidation mechanism of dimethyl sulfide.
- Patroescu, Iulia V.,Barnes, Ian,Becker, Karl H.
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p. 17207 - 17217
(2007/10/03)
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- Atmospheric chemistry of unsaturated carbonyls: butenedial, 4-oxo-2- pentenal, 3-hexene-2,5-dione, maleic anhydride, 3H-furan-2-one, and 5-methyl-3H-furan-2-one
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As part of a study on the oxidation mechanisms of aromatics some aspects of the atmospheric chemistry of several possible products, unsaturated 1,4-dicarbonyl compounds and two furanones, have been investigated in a 1080-L reaction chamber by 296 ± 2 K in 1000 mbar of synthetic air. The results indicate that reaction with OH radicals will be an important atmospheric sink for all of the unsaturated carbonyls studied here. However, for butenedial, 4-oxo-2-pentenal, and hexene-2,5-dione the results suggest that photolysis will probably be an even stronger sink. -from Authors
- Bierbach,Barnes,Becker,Wiesen
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p. 715 - 729
(2007/10/03)
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- Photocatalytic Oxidation of Organic Acids on Quantum-Sized Semiconductor Colloids
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A detailed analysis of the reaction products and mechanisms of the photocatalytic oxidation of acetate in the presence of quantum-sized ZnO colloids (Dp ca. 40 Angstroem) is presented. The principal oxidation products and reaction intermediates are determined to be CO2, HCO2(1-), CHOCO2(1-), HCHO, CH3OOH, CH3COOOH, and H2O2. Formate and glyoxylate, which are found as intermediates in the photooxidation of acetate, also serve as effective electron donors on illuminated ZnO surfaces. The proposed relative reactivity of electron donors toward photooxidation is in the following order: CHOCO2(1-) > HCO2(1-) > HCHO > CH3CO2(1-) > H2O2 >/= CH3COOOH > CH3OOH. Observed product distributions are discussed in terms of pathways involving direct oxidation of surface-bound acetate by valence band holes (or trapped holes) and the indirect oxidation of acetate by surface-bound hydroxyl radicals. The product distribution observed at low photon fluxes is not consistent with oxidation primarily by free hydroxyl radicals. A mechanism involving the reaction of an intermediate carbon-centered radical with > ZnOH surface sites is proposed. When electron donors are strongly adsorbed to semiconductor surfaces, surface-mediated reactions appear to play a dominant role in the determination of the time-dependent product distributions.
- Carraway, Elizabeth R.,Hoffman, Amy J.,Hoffmann, Michael R.
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p. 786 - 793
(2007/10/03)
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- Fourier-transform Infrared Product Study of the Reaction of CH3O2 + HO2 over the Pressure Range 15-700 Torr at 295 K
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Fourier-transform infrared spectroscopy was used to establish methyl hydroperoxide as the dominant product of the gas-phase reaction of methylperoxy radicals with hydroperoxy radicals.Over the pressure range 15-700 torr of either air or oxygen, 92 +/- 5percent of the reaction of CH3O2 with HO2 proceeds via channel (1a): CH3O2 + HO2 -> CH3OOH + O2 (1a).Quoted errors represent 2?.This result is discussed with respect to previous kinetic and mechanistic studies of peroxy radicals and computer models of atmospheric chemistry.
- Wallington, Timothy J.
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p. 2379 - 2382
(2007/10/02)
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- Rate Constants for Reduction of substituted Methylperoxyl Radicals by Ascorbate Ions and N,N,N',N'-tetramethyl-p-phenylenediamine
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Absolute rate constants (k) for reduction of substituted methylperoxyl radicals by ascorbate ions and by TMPD (N,N,N',N'-tetramethyl-p-phenylenediamine) in aqueous solutions have been determined by pulse radiolysis.The rate constants vary from 1E6 to 1E9 M-1 s-1, increasing as the electron-withdraving capacity of the substituent on the peroxyl group increases.Linear correlations are observed between log k and the Taft substituents ?* for a wide variety of substituents, but not all substituents fit the same line.In the case of ascorbate as reductant, the points for peroxyl radicals that contain halogens on the α-carbon lie on a different line (ρ*=0.41) than that for the other substituents (ρ*=1.25).In the case of TMPD there are alsotwo families of peroxyl radicals: Those comprimising the electron-donating groups Me through t-Bu (ρ=5.6) and those containing electron-withdrawing substituents (ρ*=0.64).
- Neta, P.,Huie, R. E.,Mosseri, S.,Shastri, L. V.,Mittal, J. P.,et al.
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p. 4099 - 4104
(2007/10/02)
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- Study of the Reaction ClO + CH3O2 --> Products at 300 K
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The first experimental study of the reaction ClO + CH3O2 --> products (1) is reported.The rate coefficient k1 and the product distribution were investigated in the modulated photolysis of Cl2/CH4/Cl2O/O2 mixtures.Reactants and products have been monitored by using UV-vis and Fourier-transform infrared gas-phase absorption spectroscopies.The value of k1 was found to be equal to (3.1 +/- 1.7)E-12 cm3 molecule-1 s-1 at 300 K and 240 Torr total pressure.The product channnel forming ClOO and CH3O appears to be dominant pathway at 300 K.The subsequent oxidation of CH3O to CH2O and its partial photolysis into H and HCO leads to enhanced production of odd hydrogen (OH, HO2) radicals.Consequently, high concentrations of OH radicals can built up, leading to an additional source of active chlorine via the reaction HCl + OH --> Cl + H2O, which destroys ozone by catalytic reactions.This strongly suggests that reaction 1 can play a substantial role in the photochemical processes that take place under stratospheric "ozone hole" conditions.
- Simon, F. G.,Burrows, J. P.,Schneider, W.,Moortgat, G. K.,Crutzen, P. J.
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p. 7807 - 7813
(2007/10/02)
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