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2016, Vol. 25, No. 6　Online: 2016-11-15


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Multifarious roles of carbon quantum dots in photocatalysis

 

Prof. Xu and coworkers present an overview to elaborate multifarious roles of carbon quantum dots in photocatalysis, including photoelectron mediator and acceptor, photosensitizer, photocatalyst, reducing agent for metal salt, enhancing adsorption capacity and spectral converter.

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Preface

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Special Issue on Catalytic Activation and Selective Conversion of Energy-Related Molecules Ye Wang 2016, 25(6): 0-0.  摘要 ( 2453 )   PDF(414KB) ( 4 )

PERSPECTIVES

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Cobalt-copper based catalysts for higher terminal alcohols synthesis via Fischer-Tropsch reaction Yizhi Xiang, Norbert Kruse 2016, 25(6): 895-906.  DOI: 10.1016/j.jechem.2016.09.014 摘要 ( 4473 )   The production of higher terminal alcohols through CO hydrogenation according to the Fischer-Tropsch (F-T) process has been a topic of interest since the Institut Français du Pétrole (IFP) demonstrated shortchain C1-C6 mixed alcohols production over cobalt-copper based catalysts. A number of catalyst formulations were screened for their suitability at that time. In particular, the addition of Cr, Zn, Al, Mn and V to CoCu was investigated. In a number of patents, it was shown that catalyst preparation is crucial in these catalyst formulations and that high alcohols selectivity can only be achieved by carefully respecting the procedures and recipes. This short critical review highlights recent developments in CoCu-based catalysts for higher terminal alcohols synthesis via F-T synthesis. Special attention will be given to catalyst preparation which according to developments in our group is based on oxalate precipitation. This way we show that the close association of Co and Cu on the one hand and promoter/dispersant on the other are of utmost importance to ensure high performance of the catalysts. We shall concentrate on "CoCuMn", "CoCuMo" and "CoCuNb" catalyst formulations, all prepared via oxalate precipitation and combined with "entrainment techniques" if necessary, and show high total alcohols selectivity can be obtained with tunable Anderson-Schulz-Flory chain-lengthening probability. Either long-chain C8-C14 terminal alcohols as feedstock for plasticizers, lubricants and detergents, or short-chain C2-C5 alcohols as "alkanol" fuels or fuel additives can be formed this way.

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Towards a green bulk-scale biobutanol from bioethanol upgrading Qi Zhang, Jing Dong, Yongmei Liu, Yangdong Wang, Yong Cao 2016, 25(6): 907-910.  DOI: 10.1016/j.jechem.2016.08.010 摘要 ( 4241 )   Biobutanol is attracting increasingly interest as a source of renewable energy and biofuels because of its many advantages over bioethanol that include higher energy density, fuel efficiency, and reduced engine damages. Currently, there is a growing interest in producing biobutanol from bioethanol, in view of the tremendous potential benefits of this transformation for the bulk production of biobutanol in a target specific manner. This perspective paper describes recent progress for the ethanol to butanol process. The different catalysts, including homogeneous and heterogeneous catalytic systems, for ethanol to butanol are outlined and compared, and the key issues and requirements for future developments are highlighted. A major challenge for further development and application of ethanol to butanol process is to find an optimal balance between different catalytic functions and to suppress the formation of side products that has plagued most catalytic bioethanol upgrading systems.

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Iron-based Fischer-Tropsch synthesis of lower olefins: The nature of χ-Fe5C2 catalyst and why and how to introduce promoters Di Wang, Bingxu Chen, Xuezhi Duan, De Chen, Xinggui Zhou 2016, 25(6): 911-916.  DOI: 10.1016/j.jechem.2016.11.002 摘要 ( 4645 )   As a sustainable and short-flow process, iron-catalyzed direct conversion of CO-rich syngas to lower olefins without intermediate steps, i.e., Fischer-Tropsch-to-Olefins (FTO), has received increasing attention. However, its fundamental understanding is usually limited by the complex crystal phase composition in addition to the interferences of the promoter effects and inevitable catalyst deactivation. Until recently, the combination of multiple in-situ/ex-situ characterizations and theoretical studies has evidenced Hägg iron carbide (χ-Fe5C2) as the dominant active phase of iron-based Fischer-Tropsch catalysts. This perspective attempts to review and discuss some recent progresses on the nature of χ-Fe5C2 catalyst and the crucial effects of promoters on the FTO performance from theoretical and experimental viewpoints, aiming to provide new insights into the rational design of iron-based FTO catalysts.

REVIEWS

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Development of tailored TiO2 mesocrystals for solar driven photocatalysis Peng Zhang, Mamoru Fujitsuka, Tetsuro Majima 2016, 25(6): 917-926.  DOI: 10.1016/j.jechem.2016.11.012 摘要 ( 4276 )   Ordered metal oxides superstructures have attracted much more attention in the fields of fuel generation and environmental purification owing to their unique physiochemical characteristics such as large surface area, fine pore structure, efficient electronic mobility, and good stability. Very recently, TiO2 mesocrystals (TMCs) having superstructures self-assembled by TiO2 nanoparticle building blocks, are of considerable interest in current research and application ranging from UV to visible light attributed to their efficient charge separation and superior photocatalytic activity. In this review, we describe the common procedures to prepare unique TMCs and overview of recent developments of TMCs during last 3 years, especially the structure-related or electronic-effected mechanism in photocatalytic reaction. Further, we introduce the characterization and fundamental properties of modified TMCs by the means of single-particle fluorescence microscopy for unraveling the charge transport and photocatalytic properties of individual TMCs and time-resolved diffuse reflectance spectroscopy (TDR) for monitoring the charge transfer dynamics. Finally, various aspects on TMCs are discussed for the future developments of energy and environmental fields.

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Multifarious roles of carbon quantum dots in heterogeneous photocatalysis Kang-Qiang Lu, Quan Quan, Nan Zhang, Yi-Jun Xu 2016, 25(6): 927-935.  DOI: 10.1016/j.jechem.2016.09.015 摘要 ( 3972 )   As a new member of carbon material family, carbon quantum dots (CQDs) have attracted tremendous attentions for their potentials in the heterogeneous photocatalysis applications. Due to the unique microstructure and optical properties, the roles of CQDs played in the CQDs-based photocatalytic systems have been found to be diverse with the continuous researches in this regard. Herein, we provide a concise minireview to elaborate the multifarious roles of CQDs in photocatalysis, including photoelectron mediator and acceptor, photosensitizer, photocatalyst, reducing agent for metal salt, enhancing adsorption capacity and spectral converter. In addition, the perspectives on future research trends and challenges are proposed, which are anticipated to stimulate further research into this promising field on designing a variety of efficient CQDs-based photocatalysts for solar energy conversion.

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Heterogeneous catalytic partial oxidation of lower alkanes (C1-C6) on mixed metal oxides Jacques C. Vedrine 2016, 25(6): 936-946.  DOI: 10.1016/j.jechem.2016.10.007 摘要 ( 4941 )   This review paper aims at analysing the state of the art for partial oxidation and oxidative dehydrogenation (ODH) reactions of lower alkanes C1-C6 into olefins and oxygenated products (aldehydes, anhydrides, carboxylic acids) on metal oxide catalysts with cations of variable oxidation state, such as Mo and V in particular. Key parameters to be met by the catalysts, such as their redox properties, their structural aspects, active sites composed of ensembles of atoms isolated one from the others, mechanisms of reactions, are discussed. Main features of the different reactions of C1-C6 alkanes and catalysts are analysed and their generalisation for determining more active and more selective catalysts is attempted. Prospective views for the future of the domain are proposed.

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Selective extraction and conversion of lignin in actual biomass to monophenols: A review Zhicheng Jiang, Changwei Hu 2016, 25(6): 947-956.  DOI: 10.1016/j.jechem.2016.10.008 摘要 ( 4121 )   Our over dependency on the fossil resource for industrial chemicals and fuels faces great challenges. Recently, the production of monophenols from lignin in lignocellulosic biomass is regarded as a promising process for sustainable biofuels. This article discusses the conversion of lignin in actual biomass directly to monophenols. The two step way including extraction of lignin from biomass and further degradation of the lignin oligomers to monophenols is especially discussed. The obtained monophenols can also be converted to chemicals with low-oxygen content via hydrodeoxygenation process. For extraction of lignin, co-solvent system is the most adopted for hydrolysis or solvolysis of lignin assisted by acid or alkaline catalysts. The structure of the obtained oligomers derived from lignin is discussed in detail. For lignin depolymerization, hydrogenolysis is an efficient method with the use of gaseous hydrogen or alcohols as hydrogen source. At the meantime, depolymerization mechanism and the route for repolymerization of the reaction intermediates are presented here. In hydrodeoxygenation process, metal catalysts, especially noble metal catalysts are required. The precise effects of the reaction solvents and catalysts on extraction and degradation of lignin need to be further investigated, and this will benefit to design more efficient strategies for lignin utilization.

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Nanocarbons and their hybrids as catalysts for non-aqueous lithium-oxygen batteries Yunchuan Tu, Dehui Deng, Xinhe Bao 2016, 25(6): 957-966.  DOI: 10.1016/j.jechem.2016.10.012 摘要 ( 4967 )   Rechargeable lithium-oxygen (Li-O2) batteries have been considered as the most promising candidates for energy storage and conversion devices because of their ultra high energy density. Until now, the critical scientific challenges facing Li-O2 batteries are the absence of advanced electrode architectures and highly efficient electrocatalysts for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), which seriously hinder the commercialization of this technology. In the last few years, a number of strategies have been devoted to exploring new catalysts with novel structures to enhance the battery performance. Among various of oxygen electrode catalysts, carbon-based materials have triggered tremendous attention as suitable cathode catalysts for Li-O2 batteries due to the reasonable structures and the balance of catalytic activity, durability and cost. In this review, we summarize the recent advances and basic understandings related to the carbon-based oxygen electrode catalytic materials, including nanostructured carbon materials (one-dimensional (1D) carbon nanotubes and carbon nanofibers, 2D graphene nanosheets, 3D hierarchical architectures and their doped structures), and metal/metal oxide-nanocarbon hybrid materials (nanocarbon supporting metal/metal oxide and nanocarbon encapsulating metal/metal oxide). Finally, several key points and research directions of the future design for highly efficient catalysts for practical Li-O2 batteries are proposed based on the fundamental understandings and achievements of this battery field.

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Nanostructured energy materials for electrochemical energy conversion and storage: A review Xueqiang Zhang, Xinbing Cheng, Qiang Zhang 2016, 25(6): 967-984.  DOI: 10.1016/j.jechem.2016.11.003 摘要 ( 4412 )   Nanostructured materials have received tremendous interest due to their unique mechanical/electrical properties and overall behavior contributed by the complex synergy of bulk and interfacial properties for efficient and effective energy conversion and storage. The booming development of nanotechnology affords emerging but effective tools in designing advanced energy material. We reviewed the significant progress and dominated nanostructured energy materials in electrochemical energy conversion and storage devices, including lithium ion batteries, lithium-sulfur batteries, lithium-oxygen batteries, lithium metal batteries, and supercapacitors. The use of nanostructured electrocatalyst for effective electrocatalysis in oxygen reduction and oxygen evolution reactions for fuel cells and metal-air batteries was also included. The challenges in the undesirable side reactions between electrolytes and electrode due to high electrode/electrolyte contact area, low volumetric energy density of electrode owing to low tap density, and uniform production of complex energy materials in working devices should be overcome to fully demonstrate the advanced energy nanostructures for electrochemical energy conversion and storage. The energy chemistry at the interfaces of nanostructured electrode/electrolyte is highly expected to guide the rational design and full demonstration of energy materials in a working device.

ARTICLES

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Systematic variation of the sodium/sulfur promoter content on carbon-supported iron catalysts for the Fischer-Tropsch to olefins reaction Martin Oschatz, Nynke Krans, Jingxiu Xie, Krijn P. de Jong 2016, 25(6): 985-993.  DOI: 10.1016/j.jechem.2016.10.011 摘要 ( 4397 )   The Fischer-Tropsch to olefins (FTO) process is a method for the direct conversion of synthesis gas to lower C2-C4 olefins. Carbon-supported iron carbide nanoparticles are attractive catalysts for this reaction. The catalytic activity can be improved and undesired formation of alkanes can be suppressed by the addition of sodium and sulfur as promoters but the influence of their content and ratio remains poorly understood and the promoted catalysts often suffer from rapid deactivation due to particle growth. A series of carbon black-supported iron catalysts with similar iron content and nominal sodium/sulfur loadings of 1-30/0.5-5 wt% with respect to iron are prepared and characterized under FTO conditions at 1 and 10 bar syngas pressure to illuminate the influence of the promoter level on the catalytic properties. Iron particles and promoters undergo significant reorganization during FTO operation under industrially relevant conditions. Low sodium content (1-3 wt%) leads to a delay in iron carbide formation. Sodium contents of 15-30 wt% lead to rapid loss of catalytic activity due to the covering of the iron surface with promoters during particle growth under FTO operation. Higher activity and slower loss of activity are observed at low promoter contents (1-3 wt% sodium and 0.5-1 wt% sulfur) but a minimum amount of alkali is required to effectively suppress methane and C2-C4 paraffin formation. A reference catalyst support (carbide-derived carbon aerogel) shows that the optimum promoter level depends on iron particle size and support pore structure.

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Fischer-Tropsch synthesis on impregnated cobalt-based catalysts:New insights into the effect of impregnation solutions and pH value Chuang Xing, Peipei Ai, Peipei Zhang, Xinhua Gao, Ruiqin Yang, Noriyuki Yamane, Jian Sun, Prasert Reubroycharoen, Noritatsu Tsubaki 2016, 25(6): 994-1000.  DOI: 10.1016/j.jechem.2016.09.008 摘要 ( 4412 )   The Co-based catalysts were prepared with different cobalt acetate solutions. Effects of pH value were studied deeply on Fischer-Tropsch synthesis (FTS) through a semi-batch reactor. Among all impregnation solutions (water, butanol, amyl alcohol, acetic acid, nitric acid and ammonium nitrate), the catalyst prepared by NH4NO3 solution showed the highest catalytic activity due to its small particle size and high reduction degree. However, the catalyst with the smallest particle size derived from water as impregnation solution exhibited low activity as well as high methane selectivity since it was difficult to be reduced and inactive in FTS. According to FT-IR spectra results, the low intensity of absorbed CO on the catalyst prepared from water solution resulted in low FTS activity. Whereas, the high activity of catalysts prepared from NH4NO3 solution could be explained by the high intensity of absorbed CO on the catalysts. The cobalt species on the catalysts prepared under lower pH conditions exhibited smaller particle size distribution as well as lower CO conversion than those prepared at higher pH value.

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Solvent-free synthesis of alumina supported cobalt catalysts for Fischer-Tropsch synthesis Mengnan Lu, Nouria Fatah, Andrei Y. Khodakov 2016, 25(6): 1001-1007.  DOI: 10.1016/j.jechem.2016.11.009 摘要 ( 4149 )   A novel mechano-synthesis method has been elaborated in this work for the design of efficient cobaltbased Fischer-Tropsch catalysts. The process aims to reduce the total number of steps involved in the synthesis of solid catalysts and thus to avoid relevant toxic solutions generated during the catalyst preparation. The mechano-synthesis of the Co/Al2O3 catalyst was processed in a low-energy vibratory micro mill and high energy planetary ball mill. Porous spherical γ-aluminas (1860 μm and 71 μm mean particle diameter) were used in this work as host compounds. Co3O4 (3 μm mean particle diameter) has provided guest particles for mechano-synthesis. The catalysts were characterized by textural (surface area, porosity and particle size) and structural analyses (X-ray diffraction, TPR, SEM-EDX and microprobe). The microprobe images show deposition of Co3O4 on the surface of the alumina and indicated no Co3O4 diffusion inside the alumina pores. SEM-EDX mapping illustrated that cobalt coating tended to occur on surface of rounded shape of cracked alumina fragments. After milling, the crystallite size of Co3O4 decreased to 15 nm from 30 to 50 nm. The TPR profiles indicated very low concentrations of inactive cobalt aluminate mixed compounds which are usually produced during the catalyst preparation by impregnation. In Fischer-Tropsch synthesis, the catalysts prepared using mechano-synthesis methods showed catalytic performance comparable to the catalysts prepared by impregnation.

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Reaction mechanism of aqueous-phase conversion of γ-valerolactone (GVL) over a Ru/C catalyst Abigail Rozenblit, Adam J. Avoian, Qiaohua Tan, Tawan Sooknoi, Daniel E. Resasco 2016, 25(6): 1008-1014.  DOI: 10.1016/j.jechem.2016.11.010 摘要 ( 4391 )   The present work explores the reaction pathways of γ-valerolactone (GVL) over a supported ruthenium catalyst. The conversion of GVL in aqueous phase over a 5% Ru/C catalyst was investigated in a batch reactor operating at 463 K under 500-1000 psi of H2. The main reaction products obtained under these conditions were 2-butanol (2-BuOH), 1,4-pentanediol (1,4-PDO), 2-methyltetrahydrofuran (2-MTHF) and 2-pentanol (2-PeOH). A complete reaction network was developed, identifying the primary and/or secondary products. In this reaction network, production of 2-BuOH via decarbonylation of a ring-opened surface intermediate CH3CH(O*)(CH2)2-CO* is clearly the dominant pathway. From the evolution of products as a function of reaction time and theoretical (DFT) calculations, a mechanism for the formation of intermediates and products is proposed. The high sensitivity of 2-BuOH production to the presence of CO, compared to a much lower effect on the production of the other products indicates that the sites responsible for decarbonylation are particularly prone to CO adsorption and poisoning. Also, since the decarbonylation rate is not affected by the H2 pressure it is concluded that the direct decarbonylation path of the CH3CH(O*)(CH2)2-CO* intermediate does not required a previous dehydrogenation step, as is the case in decarbonylation of short alcohols.

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High-yield production of 2,5-dimethylfuran from 5-hydroxymethylfurfural over carbon supported Ni-Co bimetallic catalyst Panpan Yang, Qineng Xia, Xiaohui Liu, Yanqin Wang 2016, 25(6): 1015-1020.  DOI: 10.1016/j.jechem.2016.08.008 摘要 ( 2 )   The catalytic conversion of 5-hydroxymethylfurfural (HMF) to 2,5-dimethylfuran (DMF) has attracted extensive research interests because DMF can be used as potential and competitive renewable transportation fuel or additives. Here we report a non-noble bimetallic catalyst with improved activity for hydrogenation and hydrogenolysis by introducing active carbon as support into a nickel-cobalt catalyst. The characterizations of the catalyst indicate that the Ni and Co species are uniformly dispersed on the active carbon through the wetness impregnation method. The influences of reaction temperature and hydrogen pressure are systematically investigated and an excellent yield (up to 95%) of DMF can be obtained at relatively mild conditions, 130℃ and 1MPa H2, over the carbon supported Ni-Co bimetallic catalyst. The high catalytic activity originates from the synergistic effect between Ni and CoOx species, the high BET surface area of the catalyst, and the uniform dispersion of Ni and Co species on the active carbon. The catalyst could be reused for 5 times without loss of activity in a batch reactor. Futhermore, the conversion of HMF to DMF on a fixed-bed reactor was also investigated and the 2%Ni-20%Co/C catalyst exhibited an excellent yield to DMF (>90%) for 71 h time on stream, indicating the high activity and stability of the catalyst.

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Catalytic performance of iron oxide loaded on electron-rich surfaces of carbon nitride Zhen Dong, Tao Wang, Jie Zhao, Teng Fu, Li Wang, Jinlin Li, Weiping Ding 2016, 25(6): 1021-1026.  DOI: 10.1016/j.jechem.2016.10.005 摘要 ( 8 )   Carbon nitride (CN) in CN encapsulated Ni/Al2O3 (denoted as CN/Ni/Al2O3) catalyst was evidenced previously as a material in electron-rich state and possessed H2-dissociative adsorption activity due to the electron doping effect from underlying nickel. In this report, iron oxide loaded on the CN/Ni/Al2O3 was synthesized and investigated by Fischer-Tropsch (F-T) synthesis to test the special effect of electron-rich support on the catalytic activity of iron oxide. The Fe/CN/Al2O3 and CN/Ni/Al2O3 samples were accordingly synthesized for comparison. In Fe/CN/Ni/Al2O3, the iron oxide was reduced to magnetite by syngas as evidenced by the in-situ XPS measurements and XRD pattern of used catalyst. Compared with Fe/CN/Al2O3, more light hydrocarbons over Fe/CN/Ni/Al2O3 were observed. It should be understood by the interaction between iron oxide and support mainly due to the effect of electron-rich state and thus enhanced H2 adsorption ability. In addition, such a novel support facilitated the CO conversion and retarded the water-gas shift reaction and CO2 formation. The new type of adjustment on electronic state should be useful for novel catalyst design.

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The thermodynamics analysis and experimental validation for complicated systems in CO2 hydrogenation process Chunmiao Jia, Jiajian Gao, Yihu Dai, Jia Zhang, Yanhui Yang 2016, 25(6): 1027-1037.  DOI: 10.1016/j.jechem.2016.10.003 摘要 ( 100 )   Catalytic conversion of CO2 into chemicals and fuels is an alternative to alleviate climate change and ocean acidification. The catalytic reduction of CO2 by H2 can lead to the formation of various products:carbon monoxide, carboxylic acids, aldehydes, alcohols and hydrocarbons. In this paper, a comprehensive thermodynamics analysis of CO2 hydrogenation is conducted using the Gibbs free energy minimization method. The results show that CO2 reduction to CO needs a high temperature and H2/CO2 ratio to achieve a high CO2conversion. However, synthesis of methanol from CO2 needs a relatively high pressure and low temperature to minimize the reverse water-gas shift reaction. Direct CO2 hydrogenation to formic acid or formaldehyde is thermodynamically limited. On the contrary, production of CH4 from CO2 hydrogenation is the thermodynamically easiest reaction with nearly 100% CH4 yield at moderate conditions. In addition, complex reactions with more than one product are also calculated in this work. Among the considered carboxylic acids (HCOOH, CH3COOH and C2H5COOH), propionic acid dominates in the product stream (selectivity above 90%). The same trend can also be found in the hydrogenation of CO2 to aldehydes and alcohols with the major product of propionaldehyde and butanol, respectively. In the process of CO2 hydrogenation to alkenes, low temperature, high pressure, and high H2 partial pressure favor the CO2 conversion. C4H6 is the most thermodynamically favorable among all considered alkynes under different temperatures and pressures. The thermodynamic calculations are validated with experimental results, suggesting that the Gibbs free energy minimization method is effective for thermodynamically understanding the reaction network involved in the CO2 hydrogenation process, which is helpful for the development of high-performance catalysts.

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Synergistic effects of bimetallic Cu-Fe/SiO2 nanocatalysts in selective hydrogenation of diethyl malonate to 1,3-propanediol Le He, Xiaoxiao Gong, Linmin Ye, Xinping Duan, Youzhu Yuan 2016, 25(6): 1038-1044.  DOI: 10.1016/j.jechem.2016.11.007 摘要 ( 19 )   Cux-Fey/SiO2 catalysts were prepared using urea-assisted sol-gel method. The structure and physicochemical properties of the catalysts were characterized using N2 adsorption-desorption, transmission electron microscopy, H2-temperature-programmed reduction, powder X-ray diffraction, and X-ray photoelectron spectroscopy. Compared with monometallic Cu or Fe catalysts, the bimetallic Cux-Fey/SiO2 catalysts exhibited enhanced catalytic performance for the selective hydrogenation of diethyl malonate to 1,3-propanediol. The bimetallic catalyst with an optimal Cu/Fe atomic ratio of 2 exhibited the highest activity, which yielded 96.3% conversion to diethyl malonate and 93.3% selectivity to 1,3-propanediol under the optimal reaction conditions. Characterization results revealed that interactions between Cu and Fe contributed to the improvement of diethyl malonate conversion and selectivity to 1,3-propanediol. The X-ray photoelectron spectroscopy results revealed that the addition of appropriate amount of Fe species enhanced the reduction of Cu2+ species, thereby increasing the Cu0 species on the surface of bimetallic catalyst. It led to a better chemisorption capacity of hydrogen and further promoted of the activation of hydrogen molecule. The ethyl acetate temperature-programmed desorption results indicated that the FeOy species provided the additional adsorption sites for substrate molecules, and they activated the C=O bond. The improved catalytic performance of bimetallic Cux-Fey/SiO2 catalyst was mainly attributed to the synergistic effect between Cu0 and FeOy species.

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The mechanism of hydrogen abstraction by high valence transition metal oxo compounds Gang Fu, Ruming Yuan, Huilin Wan, Xin Xu 2016, 25(6): 1045-1050.  DOI: 10.1016/j.jechem.2016.10.006 摘要 ( 3110 )   We present here a systematic theoretical study to explore the underlying mechanisms of the H abstraction reaction from methane. Various abstracting agents have been modeled, using oxygen radicals and a set of high valence metal oxo compounds. Our calculations demonstrate that although H abstraction from CH3-H by metal oxoes can be satisfactorily fitted into the Polanyi correlation on the basis of oxygen radicals, the mechanisms behind are significantly different. The frontier orbital analyses show that there are three electrons and three active orbitals (3e,3o) involved in H abstraction by oxygen radicals; whereas an additional orbital of πM-O* is involved in H abstraction by M=O, resulting in a (4e,4o) interaction. In terms of valence bond state correlation diagram, we find that H abstraction by a metal oxo may benefit from the contribution of ionic resonance structures, which could compensate the penalty of opening the M-O π bond. We believe that these findings can help to design more effective catalysts for the activation of light alkanes.

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Identification of relevant active sites and a mechanism study for reverse water gas shift reaction over Pt/CeO2 catalysts Xiaodong Chen, Xiong Su, Binglian Liang, Xiaoli Yang, Xinyi Ren, Hongmin Duan, Yanqiang Huang, Tao Zhang 2016, 25(6): 1051-1057.  DOI: 10.1016/j.jechem.2016.11.011 摘要 ( 7 )   Reverse water gas shift (RWGS) reaction can serve as a pivotal stage in the CO2 conversion processes, which is vital for the utilization of CO2. In this study, RWGS reaction was performed over Pt/CeO2 catalysts at the temperature range of 200-500℃ under ambient pressure. Compared with pure CeO2, Pt/CeO2 catalysts exhibited superior RWGS activity at lower reaction temperature. Meanwhile, the calculated TOF and Ea values are approximately the same over these Pt/CeO2 catalysts pretreated under various calcination conditions, indicating that the RWGS reaction is not affected by the morphologies of anchored Pt nanoparticles or the primary crystallinity of CeO2. TPR and XPS results indicated that the incorporation of Pt promoted the reducibility of CeO2 support and remarkably increased the content of Ce3+ sites on the catalyst surface. Furthermore, the CO TPSR-MS signal under the condition of pure CO2 flow over Pt/CeO2 catalyst is far lower than that under the condition of adsorbed CO2 with H2-assisted flow, revealing that CO2 molecules adsorbed on Ce3+ active sites have difficult in generating CO directly. Meanwhile, the adsorbed CO2 with the assistance of H2 can form formate species easily over Ce3+ active sites and then decompose into Ce3+-CO species for CO production, which was identified by in-situ FTIR.

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Effects of the crystallization time on the mesoporous structure, texture, morphology and styrene oxidation performances of V-MCM-41 Junqiang Xu, Qiang Zhang, Fang Guo, Jingping Hong, Wei Chu 2016, 25(6): 1058-1063.  DOI: 10.1016/j.jechem.2016.10.004 摘要 ( 6 )   The new V-MCM-41 molecular sieves with good ordered hexagonal mesoporous structure and crystallinity were synthesized through in-situ hydrothermal preparation method. The effects of the crystallization time were discussed. The synthesized samples were characterized by X-ray diffraction, N2 adsorption/desorption, Fourier transformed infrared and scanning electron microscopy. The different structures, textures, morphologies of V-MCM-41 obtained with different crystallization times were observed and analyzed on the basis of the characterized results. The results showed that the V-MCM-41 molecular sieve obtained at 110℃ for 48 h crystallization times was of good spherical morphology, ordered hexagonal structure, most uniform pore size distribution and high surface area compared with other samples. Meanwhile, the V-MCM-41 molecular sieve with the high skeleton Si condensation and the good crystallinity was obtained. The heteroatom could be incorporated into MCM-41 framework with increasing crystallization times, which was beneficial to improve the catalytic activity and selectivity of pure siliceous MCM-41. The V-MCM-41 showed the good catalytic selectivity in catalytic oxidation of styrene using hydrogen peroxide, and the selectivity of the benzaldehyde and phenylacetic acid reached 30.68% and 49.44%, respectively.

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Modified wool-iron biopolymer-based complex as an active heterogeneous decontamination photocatalyst Lizhong Zhang, Qian Zhai, Xiufeng Zhao, Xuemei Min, Qiuhui Zhu, Jianhui Li 2016, 25(6): 1064-1069.  DOI: 10.1016/j.jechem.2016.10.010 摘要 ( 6 )   A series of biopolymer based complex were manufactured by coordinating iron ions to the abundant amino- and sulfur-containing groups in the modified wool and used as heterogeneous Fenton-like photocatalyst for 4-chlorophenol (4-CP) degradation in the presence of H2O2. Hydroxylamine hydrochloride (NH2OH·HCl) or acrylic acid was employed to modify the natural wool to strengthen the interaction with iron and to reinforce the structural stability. The NH2OH·HCl modified wool based complex showed the best catalytic performance for 4-CP degradation. The strong coordination between iron and great number of hydroxamic acid in this modified complex leads to the least iron leaching during the tests. HO·species was confirmed to be the dominant reactive oxidant in the decontamination process. The approach presented in this study can provide a new approach for developing novel bioployermer-based photocatalysts for efficient degradation of toxic organic pollutants such as 4-CP.

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CO2 selective hydrogenation to synthetic natural gas (SNG) over four nano-sized Ni/ZrO2 samples: ZrO2 crystalline phase & treatment impact Min Chen, Zhanglong Guo, Jian Zheng, Fangli Jing, Wei Chu 2016, 25(6): 1070-1077.  DOI: 10.1016/j.jechem.2016.11.008 摘要 ( 5 )   Two type zirconia (monoclinic and tetragonal phase ZrO2) carriers were synthesized via hydrothermal route, and nano-sized zirconia supported nickel catalysts were prepared by incipient impregnation then followed thermal treatment at 300℃ to 500℃, for the CO2 selective hydrogenation to synthetic natural gas (SNG). The catalysts were characterized by XRD, CO2-TPD-MS, XPS, TPSR (CH4, CO2) techniques. For comparison, the catalyst NZ-W-400 (monoclinic) synthesized in water solvent exhibited a better catalytic activity than the catalyst NZ-M-400 (tetragonal) prepared in methanol solvent. The catalyst NZ-W-400 displayed more H2 absorbed sites, more basic sites and a lower temperature of initial CO2 activation. Then, the thermal treatment of monoclinic ZrO2 supported nickel precursor was manufactured at three temperature of 350, 400, 500℃. The TPSR experiments displayed that there were the lower temperature for CO2 activation and initial conversion (185℃) as well as the lower peak temperature of CH4 generation (318℃), for the catalyst calcined at 500℃. This sample contained the more basic sites and the higher catalytic activity, evidenced byCO2-TPD-MS and performance measurement. As for the NZ-W-350 sample, which exhibited the less basic sites and the lower catalytic activity, its initial temperature for CO2 activation and conversion was higher (214℃) as well as the higher peak temperature of CH4 formation (382℃).

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Improvement of catalytic stability for CO2 reforming of methane by copper promoted Ni-based catalyst derived from layered-double hydroxides Bing Li, Zhenxin Xu, Fangli Jing, Shizhong Luo, Ning Wang, Wei Chu 2016, 25(6): 1078-1085.  DOI: 10.1016/j.jechem.2016.11.001 摘要 ( 9 )   Copper-promoted nickel-based metal nanoparticles (NPs) with high dispersion and good thermal stability were derived from layered-double hydroxides (LDHs) precursors that were facilely developed by a coprecipitation strategy. The copper-promoted Ni-based metal NPs catalysts were investigated for methane reforming with carbon dioxide to hydrogen and syngas. A series of characterization techniques including XRD, N2 adsorption and desorption, H2-TPR, XPS, CO2-TPD, TEM, TGA and in situ CH4-TPSR were utilized to determine the structure-function relationship for the obtained catalysts. The copper addition accelerated the catalyst reducibility as well as the methane activation, and made the Ni species form smaller NPs during both preparation and reaction by restricting the aggregation. However, with higher copper loading, the derived catalysts were less active during methane reforming with CO2 to syngas. It was confirmed that the catalyst with 1 wt% Cu additive gave the higher catalytic activity and remained stable during long time reaction with excellent resistance to coking and to sintering. Furthermore, the mean size of metal NPs changed minimally from 6.6 to 7.9 nm even after 80 h of time on stream at temperature as high as 700℃ for this optimized catalyst. Therefore, this high dispersed anti-coking copper-promoted nickel catalyst derived from LDHs precursor could be prospective catalyst candidate for the efficient heterogeneous catalysis of sustainable CO2 conversion.