能源化学(英文版)

Select

Modified solid acids derived from biomass based cellulose for one-step conversion of carbohydrates into ethyl levulinate

Jun Zhang, Jinzhu Chen

2016, 25(5): 747-753. DOI: 10.1016/j.jechem.2016.06.005

摘要 ( 4138 )

A series of metal salt-modified carbon catalysts had been prepared to study the selective transformation of various carbohydrates into ethyl levulinate in an ethanol medium. The specific textural and chemical characteristics of prepared carbon samples were identified by Raman, XRD, XPS, NH₃-TPD, FT-IR and nitrogen physisorption. Various parameters such as ethanol/water volume ratio, NaCl addition, reaction temperature, and catalyst dosage played a great role in ethyl levulinate production. A desirable ethyl levulinate yield of 58.0 mol% with a highest ROF (rate of ethyl levulinate formation per gram of catalyst per hour) value of 2148.3 μmol/(g_cat·h) was achieved at 468 K over FeCl₃ modified carbon catalyst with respect to fructose conversion. The recycling experiments revealed that the sulfonated carbon catalysts exhibited relatively satisfied activity and stability.

Select

First assessment of Li₂O-Bi₂O₃ ceramic oxides for high temperature carbon dioxide capture

E. M. Briz-López, M. J. Ramírez-Moreno, I. C. Romero-Ibarra, C. Gómez-Yáñez, H. Pfeiffer, J. Ortiz-Landeros

2016, 25(5): 754-760. DOI: 10.1016/j.jechem.2016.05.001

摘要 ( 3781 )

The capacity to capture CO₂ was determined in several stoichiometric compositions in the Li₂O-Bi₂O₃ system. The compounds (Li₇BiO₆, Li₅BiO₅, Li₃BiO₄ and LiBiO₂ phases) were synthesized via solid-state reaction and characterized by X-ray diffraction, scanning electron microscopy and N₂ adsorption techniques. The samples were heat-treated at temperatures from 40 to 750 ℃ under the CO₂ atmosphere to evaluate the carbonate formation, which is indicative of the capacity of CO₂ capture. Moreover, Li₇BiO₆ shows an excellent CO₂ capture capacity of 7.1 mmol/g, which is considerably higher than those of other previously reported ceramics. Li₇BiO₆ is able to react with CO₂ from 240 ℃ to approximately 660 ℃ showing a high kinetic reaction even at CO₂ partial pressure values as low as 0.05.

Select

Hard carbon derived from cellulose as anode for sodium ion batteries: Dependence of electrochemical properties on structure

V. Simone, A. Boulineau, A. de Geyer, D. Rouchon, L. Simonin, S. Martinet

2016, 25(5): 761-768. DOI: 10.1016/j.jechem.2016.04.016

摘要 ( 5662 )

Cellulose, the most abundant organic polymer on Earth, is a sustainable source of carbon to use as a negative electrode for sodium ion batteries. Here, hard carbons (HC) prepared by cellulose pyrolysis were investigated with varying pyrolysis temperature from 700 ℃ to 1600 ℃. Characterisation methods such as Small Angle X-ray Scattering (SAXS) measurements and N₂ adsorption were performed to analyse porosity differences between the samples. The graphene sheet arrangements were observed by transmission electron microscopy (TEM): an ordering of the graphene sheets is observed at temperatures above 1150 ℃ and small crystalline domains appear over 1400 ℃. As the graphene sheets start to align, the BET surface area decreases and the micropore size increases. To correlate hard carbon structures and electrochemical performances, different tests in Na//HC cells with 1 M NaPF 6 ethylene carbonate/dimethyl carbonate (EC/DMC) were performed. Samples pyrolysed from 1300 ℃ to 1600 ℃ showed a 300 mAh/g reversible capacity at C/10 rate (where C = 372 mA/g) with an excellent stability in cycling and a very good initial Coulombic efficiency of up to 84%. Furthermore, hard carbons showed an excellent rate capability where sodium extraction rate varies from C/10 to 5 C. At 5 C more than 80% of reversible capacity remains stable for hard carbons synthesized from 10 0 0 ℃ to 1600 ℃.

Select

A new D-D-π-A dye for efficient dye-sensitized solar cells

Xiaoqiang Yu, Huailing Jiang, Yi Wang, Yantao Shi, Tingli Ma, Ming Bao

2016, 25(5): 769-774. DOI: 10.1016/j.jechem.2016.05.005

摘要 ( 3681 )

New metal-free organic dye sensitizers containing mono-triphenylamine or bis-triphenylamine as the electron donor, a thiophene as the π-conjugated system, and a cyanoacrylic acid moiety as the electron acceptor were synthesized. The optical and electrochemical properties of the dyes were investigated, and their performance as sensitizers in solar cells was evaluated. Dye-sensitized solar cells based on dye containing bis-triphenylamine as the electron donor produced a photon-to-current conversion efficiency of 6.06% (Jsc = 14.21 mA/cm², Voc = 0.62 V, ff = 0.69) under 100 mW/cm² simulated AM 1.5 G solar irradiation (100 mW/cm 2).

Select

One-step synthesis of dimethyl ether from syngas on ordered mesoporous copper incorporated alumina

Yan Wang, Yuexian Chen, Feng Yu, Dahai Pan, Binbin Fan, Jinghong Ma, Ruifeng Li

2016, 25(5): 775-781. DOI: 10.1016/j.jechem.2016.04.014

摘要 ( 3989 )

Ordered mesoporous copper incorporated Al₂O₃ (Cu/Al₂O₃) with high Cu dispersion were prepared by a facile solution combustion synthesis method using aluminum nitrate and copper nitrate as oxidants and urea as fuel. It is a facile and green route to synthesize catalysts for dimethyl ether directly from syngas. Cu/Al₂O₃ catalysts were characterized by XRD, N₂ adsorption-desorption, SEM-EDS, and H₂-TPR. The results indicate that the catalysts obtain an ordered mesoporous structure and copper is homogenously dispersed. The mesoporous Cu/Al₂O₃ catalysts were utilized as bifunctional catalysts in syngas to dimethyl ether reaction (STD). The copper content affects the catalytic performance in STD reaction. The CO conversion and DME selectivity of Cu/Al₂O₃ with 15% copper molar ratio achieve 52.9% and 66.1%, respectively. Moreover, the mesoporous Cu/Al₂O₃ catalysts show excellent stability in STD reaction.

Select

Insight into the function of base-promoted Cu-containing catalysts for highly efficient hydrogenolysis of cellulose into polyols

Pengfei Ma, Zihui Xiao, Shaohua Jin, Chuang Li, Changhai Liang

2016, 25(5): 782-792. DOI: 10.1016/j.jechem.2016.07.001

摘要 ( 4005 )

The Cu-containing catalysts were synthesized via thermal treatment of the CuMgAl hydrotalcite with a fixed metal ratio at various calcination temperatures. The bi-functional solid base catalysts exhibited high activity for the hydrogenolysis of highly concentrated cellulose. The hydrotalcite precursors and the calcined samples were characterized by means of X-ray diffraction (XRD), thermogravimetric analysis (TG), N 2 adsorption-desorption, temperature-programmed reduction of H₂(H₂-TPR), temperature-programmed desorption of CO₂ (CO₂-TPD) and dissociative N₂O adsorption. The characterization results indicated that the transformation of structure was caused by the increasing calcination temperature, which could further influence the numbers of the base sites and metal active sites in the CuMgAl catalysts. The hydrogenolysis of cellulose was systematically investigated over different catalytic systems. With the CuMgAl-600 catalyst, complete conversion of cellulose can be accomplished and the highest yield obtained is 81.4%, with total polyols yields obtained are 59.1% for the C2-C3 polyols. In addition, either the in-situ hydroxyl or the hydrated OH^- due to the “memory effect” of hydrotalcite as Brønsted bases, was proved to exhibit promotional effect on the hydrogenolysis of cellulose, which could effectively substitute the effect of ionizing alkali. Furthermore, it is noteworthy that the conversion of cellulose could maintain up to 90.2% with unobvious formation of coke-like precipitates when the cellulose concentration reached a high level of 18%.

Select

Positively charged carbon electrocatalyst for enhanced power performance of L-ascorbic acid fuel cells

Myounghoon Choun, Hye Jin Lee, Jaeyoung Lee

2016, 25(5): 793-797. DOI: 10.1016/j.jechem.2016.05.006

摘要 ( 3679 )

Carbon surface with large oxygen and carbon ratio (O/C) indicated an outstanding electro-catalytic activity toward L-ascorbic acid oxidation, compared to platinum group metals. However, interrelation of surface functional groups and its electro-catalytic activity is still unclear. In this paper, we prepared different levels of oxidized carbons by a simple acid treatment and investigated the correlation between the surface oxygen functional groups of acid-treated carbon and electro-catalytic activity in an electrooxidation of L-ascorbic acid. Positively charged carbon was demonstrated by lone pair electron of oxygen from valence band spectra study. It was revealed that the positively charged carbon, especially involved in carbonyl, showed enhanced the electro-catalytic activity through both better adsorption of negatively charged reactants and lowered LUMO by electronegativity of oxygen.

Select

Photoelectrochemical study of MoO₃assorted morphology films formed by thermal evaporation

R. Senthilkumar, G. Anandhababu, T. Mahalingam, G. Ravi

2016, 25(5): 798-804. DOI: 10.1016/j.jechem.2016.04.005

摘要 ( 5212 )

Molybdenum oxide nanostructured thin films were grown on fluorine doped tin oxide (FTO), indium doped tin oxide (ITO) and ordinary glass substrates by thermal evaporation process without vacuum and catalysts using molybdenum trioxide (MoO₃) powder as a source material and oxygen as a carrier gas. Various morphologies including nanobelts, disks and hexagonal rod-like nanostructures were obtained by changing the source and substrate temperatures during the growth of MoO₃ thin films. Structural parameters, morphology, composition and surface features of the films were characterized by XRD, SEM, EDAX, XPS, AFM and Raman spectroscopy. The films were orthorhombic in structure with preferred orientation along (0 1 0) plane. Morphology analysis reveals randomly aligned nanobelts with 40 nm in thickness and a width of 800 nm and 3-12 mm in length. The disks have 1.5 μm diameters, 1 μm thickness and hexagonal rod-like nanostructures with a length, breath and width of 2 μm, 1 μm and 100 nm are formed. The samples were investigated under dark and photocurrent conditions in H₂SO₄ aqueous solution as a function of applied potential. The photocurrent density of samples prepared on ITO and FTO substrate samples were compared and the results are discussed.

Select

Gold-iridium bifunctional electrocatalyst for oxygen reduction and oxygen evolution reactions

Lizhi Yuan, Zhao Yan, Luhua Jiang, Erdong Wang, Suli Wang, Gongquan Sun

2016, 25(5): 805-810. DOI: 10.1016/j.jechem.2016.04.013

摘要 ( 4263 )

Carbon supported gold-iridium composite (AuIr/C) was synthesized by a facile one-step process and was investigated as the bifunctional catalyst for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). The physical properties of the AuIr/C composite were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Although the Au and Ir in the AuIr/C did not form alloy, it is clear that the introduction of Ir decreases the average Au particle size to 4.2 nm compared to that in the Au/C (10.1 nm). By systematical analysis on chemical state of metal surface via XPS and the electrochemical results, it was found that the Au surface for the Au/C can be activated by potential cycling from 0.12 V to 1.72 V, resulting in the increased surface roughness of Au, thus improving the ORR activity. By the same potential cycling, the Ir surface of the Ir/C was irreversibly oxidized, leading to degraded ORR activity but uninfluenced OER activity. For the AuIr/C, Ir protects Au against being oxidized due to the lower electronegativity of Ir. Combining the advantages of Au and Ir in catalyzing ORR and OER, the AuIr/C catalyst displays an enhanced catalytic activity to the ORR and a comparable OER activity. In the 50-cycle accelerated aging test for the ORR and OER, the AuIr/C displayed a satisfied stability, suggesting that the AuIr/C catalyst is a potential bifunctional catalyst for the oxygen electrode.

Select

Improving electrochemical activity of PtRu/SnO₂/C catalyst by reduction treatment and alkaline etching

Qi Wang, Hualong Tao, Zhiqiang Li, Chunhuan Chen, Shanshan Liu, Lei Han, Xing Lu

2016, 25(5): 811-816. DOI: 10.1016/j.jechem.2016.05.003

摘要 ( 4003 )

PtRu/SnO₂/C catalyst was prepared in a polyol process, followed by reduction treatment and alkaline etching. X-ray diffraction, transmission electron microscope with energy dispersive spectrometer and Xray photoelectron spectroscopy were used to characterize the morphology, structure and composition of the catalysts. CO and methanol electro-oxidation activities of the catalysts were evaluated by CO stripping voltammetry, cyclic voltammetry and chronoamperometry measurements. Reduction treatment of the prepared PtRuSnO₂/C catalyst in a polyol process induced the enrichment of Sn on the surface, inhibiting methanol dissolution and CO adsorption on Pt. Alkaline etching removed Sn or SnO_x and thus exposed PtRu on the surface, resulting in enhanced activities for CO and methanol electro-oxidation due to the synergy effects of PtRu on the surface and Sn species beneath.

Select

Influence of graphene oxide on electrochemical performance of Si anode material for lithium-ion batteries

Wenjing Liu, Jinjin Jiang, Hao Wang, Chunxiao Deng, Feng Wang, Gongchang Peng

2016, 25(5): 817-824. DOI: 10.1016/j.jechem.2016.06.006

摘要 ( 4252 )

We have developed a Si/graphene oxide electrode synthesized via ultrasonication-stirring method under alkaline condition. Scanning electron microscopy (SEM), transmission electron microscope (TEM), EDS dot-mapping and high-resolution transmission electron microscopy (HRTEM) results show that Si particles are evenly dispersed on the graphene oxide sheets. The electrochemical performance was investigated by galvanostatic charge/discharge tests at room temperature. The results revealed that Si/graphene oxide electrode exhibited a high reversible capacity of 2825 mAh/g with a coulombic efficiency of 94.6% at 100 mA/g after 15 cycles and a capacity retention of 70.8% after 105 cycles at 40 0 0 mA/g. These performance parameters show a great potential in the high-performance batteries application for portable electronics, electric vehicles and renewable energy storage.

Select

Dry reforming of methane on active and coke resistant Ni/Y₂Zr₂O₇ catalysts treated by dielectric barrier discharge plasma

Xiuzhong Fang, Jie Lian, Kaiwen Nie, Xianhua Zhang, Yanfeng Dai, Xianglan Xu, Xiang Wang, Wenming Liu, Changqing Li, Wufeng Zhou

2016, 25(5): 825-831. DOI: 10.1016/j.jechem.2016.06.002

摘要 ( 4110 )

In this study, Ni/Y₂Zr₂O₇ catalysts prepared with impregnation method and treated by dielectric barrier discharge plasma (DBD) in different atmospheres have been investigated for methane dry reforming. It is revealed by H₂-TPR that plasma treatment can enhance the interaction between NiO/Ni particles and the Y₂Zr₂O₇ pyrochlore support. Therefore, catalysts with smaller NiO and Ni grains sizes, higher metallic Ni active surface areas can be achieved, as evidenced by XRD, TEM and H₂ adsorption-desorption measurements. As a consequence, the plasma-treated catalysts show significantly improved activity, stability and coke resistance, as testified by the TEM and TGA-DSC results. Plasma treatment in H₂/Ar gas mixture is found to be the best condition to prepare Ni/Y₂Zr₂O₇, which can be used to obtain a catalyst with the highest activity, stability and most potent coke resistance. It is believed that the smaller Ni grain size and higher metallic Ni active surface area induced by plasma treatment are the inherent reasons accounting for the promoted reaction performance of the Ni/Y₂Zr₂O₇ pyrochlore catalysts.

Select

Improved hydrogen storage properties of MgH₂ catalyzed with K₂NiF₆

N. N. Sulaiman, N. Juahir, N. S. Mustafa, F. A. Halim Yap, M. Ismail

2016, 25(5): 832-839. DOI: 10.1016/j.jechem.2016.04.015

摘要 ( 5281 )

In this study, the hydrogen storage properties of MgH₂-X wt% K₂NiF₆ (X = 5, 10, 15, 20, and 50) were investigated for the first time. From the analysis of the onset desorption temperature and isothermal de/absorption kinetics, it was shown that MgH₂+5 wt% K₂NiF₆ sample has the best performance. The 5 wt% doped sample started to release hydrogen at about 260 ℃, which was a reduction of about 95 ℃ and 157 oC compared with the as-milled and as-received MgH₂. In addition, the de/absorption kinetics of the MgH₂+5 wt% K₂NiF₆ were also improved significantly compared to the un-doped MgH₂. The apparent activation energy for hydrogen desorption exhibited the decrement from 167.0 kJ/mol for as-milled MgH₂ to 111.0 kJ/mol with the addition of 5 wt% K₂NiF₆. Moreover, the X-ray diffraction spectra displayed the formation of new phases of KF, KH, Mg₂Ni and Mg₂NiH₄ by doping the K₂NiF₆ with MgH₂ after the dehydrogenation and rehydrogenation processes. The scanning electron microscope results revealed that MgH₂doped with 5 wt% K₂NiF₆ demonstrated the smallest particle size compared to the as-received and as-milled MgH₂. It is believed that the formation of in situ active species of KF, KH, and Mg₂Ni could provide a synergetic catalytic effect in enhancing the hydrogen sorption properties of MgH₂.

Select

Co/Fe oxide and Ce_0.8Gd_0.2O_2-δ composite interlayer for solid oxide electrolysis cell

Jingbo Yan, Lei Shang, Zhe Zhao, Dingrong Ou, Mojie Cheng

2016, 25(5): 840-844. DOI: 10.1016/j.jechem.2016.05.002

摘要 ( 3363 )

A composite interlayer comprised of gadolinia doped ceria (GDC) and Co/Fe oxide was prepared and investigated for solid oxide electrolysis cell with yttrium stabilized zirconia (YSZ) electrolyte and La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ (LSCF) anode. The interlayer was constructed of a base layer of GDC and a top layer of discrete Co₃O₄/FeCo₂O₄ particles. The presence of the GDC layer drastically alleviated the undesired reactions between LSCF and YSZ, and the presence of Co/Fe oxide led to further performance improvement. At 800 ℃ and 45% humidity, the cell with 70% Co/Fe-GDC interlayer achieved 0.98 A/cm² at 1.18 V, 14% higher than the cell without Co/Fe oxide. Electrochemical impedance spectroscopy (EIS) revealed that with higher Co/Fe content, both the ohmic resistance and the polarization resistance of the cell were reduced. It is suggested that Co/Fe oxide can react with the Sr species segregated from LSCF and Sr_1-x (Co,Fe)O_3-δ, a compound with high catalytic activity and electronic conductivity. The Sr-capturing ability of Co/Fe oxide in combination with the Sr-blocking ability of GDC layer can effectively suppress the undesired reaction between LSCF and YSZ, and consequently improve the cell performance.

Select

Graphene-wrapped Ag₃PO₄/LaCO₃OH heterostructures for water purification under visible light

Santosh S. Patil, Mukund G. Mali, Animesh Roy, Mohaseen S. Tamboli, Virendrakumar G. Deonikar, Deepak R. Patil, Milind V. Kulkarni, Salem S. Al-Deyab, Sam S. Yoon, Sanjay S. Kolekar, Bharat B. Kale

2016, 25(5): 845-853. DOI: 10.1016/j.jechem.2016.05.004

摘要 ( 4357 )

We demonstrated a unique synthesis approach of graphene (GR)-wrapped Ag₃PO₄/LaCO₃OH (APO/LCO) heterostructures by an in-situ wet chemical method. FESEM analysis reveals the formation of rhombic dodecahedrons of APO decorated with LCO and later wrapped with GR flakes. Optical studies shows two absorption edges corresponding to the band gap energies of APO (2.41 eV) and LCO (4.1 eV). Considering the absorption edge of the heterostructures in the visible region, the photocatalytic activities of photocatalysts containing different APO/LCO mass ratios were evaluated by the degradation of MB. GR-decorated composite with 20% LCO (APO/LCO20/GR) exhibited the highest photocatalytic activity for MB degradation, with a rate constant, k of 0.541 min^-1. The photocatalytic activity of APO/LCO20/GR more greatly enhanced than those of the individual constituents (APO, LCO, APO/LCO20). The enhanced photocatalytic activity of the heterostructure can be attributed to the co-catalytic effect of LCO as well as intriguing physicochemical properties of GR. To understand the enhanced photocatalytic activity of the heterostructures the photocatalytic reaction mechanism is proposed in detail. The recyclability of the APO/LCO/GR composite photocatalyst is further evaluated by reusing the catalyst in replicate photocatalytic experiments which shows consistent photocatalytic activity thereby confirms the stability and reusability of heterostructure photocatalyst.

Select

Promoter effect of La₂O₃ on gold catalyst with different textural structures

Huiyuan Xu, Jingjie Luo, Shenying Xu, Denglei Zhu, Wei Chu

2016, 25(5): 854-860. DOI: 10.1016/j.jechem.2016.06.001

摘要 ( 4217 )

Silica supported gold nanoparticles were synthesized and promoted by lanthanum oxide as dopant. The influences of La₂O₃ and silica textural structure on the gold dispersion, formation of active species, crystalline composition and the reacting role of dopants were studied in detail. The characterization results suggested that the dispersion of gold nanoparticles depended on the textural structure of silica without lanthanum oxide doping where small mesopores are more preferable to disperse gold nanoparticles. The addition of lanthanum oxide largely increased the dispersion of gold nanoparticles and oxygen active sites independent of the textural structure of silica support. The interaction between lanthanum oxide and silica enhanced by the synergy facilitated the release of oxygen vacancies and transition of active oxygen species. In addition, the chemical properties were greatly changed after lanthanum oxide addition which was only inconspicuously impacted by the initial textural structure of silica supports, shedding light on the further design of economic gold catalyst based on simple synthesis method.

Select

Theoretical design and experimental synthesis of counter electrode for dye-sensitized solar cells: Amino-functionalized graphene

Yiyi Jia, Yantao Shi, Jieshan Qiu, Ce Hao

2016, 25(5): 861-867. DOI: 10.1016/j.jechem.2016.07.002

摘要 ( 3901 )

For some specific catalytic reaction, how to construct active sites on two dimensional materials is of great scientific significance. Dye-sensitized solar cells (DSCs) can be viewed as one representative photovoltaics because in which liquid electrolyte with triiodide/iodide (I₃^-/I^-) as redox couples are involved. In this study, amino-functionalized graphene (AFG) has been designed according to theoretically analyzing iodine reduction reaction (IRR) processes and rationally screening the volcanic plot. Then, such AFG has been successfully synthesized by a simple hydrothermal method and shows high electrocatalytic activity towards IRR when serving as counter electrode in DSCs. Finally, a high conversion efficiency of 7.39% by AFG-based DSCs was obtained, which is close to that using Pt as counter electrode.

Select

Dehydrogenation characteristics of LiAlH₄ improved by in-situ formed catalysts

Jiaxing Cai, Lei Zang, Lipeng Zhao, Jian Liu, Yijing Wang

2016, 25(5): 868-873. DOI: 10.1016/j.jechem.2016.06.004

摘要 ( 4757 )

The hydrogen storage properties and catalytic mechanism of FeCl₂ -doped LiAlH₄ were investigated in minute details. LiAlH₄ -2 mol% FeCl₂ samples start to release hydrogen at 76 ℃, which is 64 ℃ lower than that of as-received LiAlH₄. Isothermal desorption measurements show that the 2 mol% FeCl₂ -doped sample releases 7.0 wt% of hydrogen within 17 min at 250 ℃. At lower temperatures of 110 ℃ and 80 ℃, the sample can release 4.4 wt% and 3 wt% of hydrogen, respectively. The apparent activation energy of LiAlH₄-2 mol% FeCl₂ samples for R2 is 105.02 kJ/mol, which is 67 kJ/mol lower than that of pure LiAlH₄. The reaction between LiAlH₄ and FeCl₂ during ball milling was found by analyzing the X-ray diffraction results, and Fe-Al particles formed in-situ from the reaction act as the real catalyst for the dehydrogenation of LiAlH₄.

Select

Zirconium-containing UiO-66 as an efficient and reusable catalyst for transesterification of triglyceride with methanol

Fan Zhou, Ningyue Lu, Binbin Fan, Huigang Wang, Ruifeng Li

2016, 25(5): 874-879. DOI: 10.1016/j.jechem.2016.06.003

摘要 ( 4135 )

Zirconium-based MOFs of the UiO family have attracted considerable attention due to their high thermal, chemical and mechanical stability. With the aim of further exploring the applications of zirconium-based UiO-66 in acid-catalyzed reactions and elucidating the effects of the defects in UiO-66 materials on their catalytic performances, in this work, a series of zirconium-containing UiO-66 samples were synthesized by varying the synthesis temperatures and BDC/Zr (terephthalic acid/ZrCl₄) ratios in the synthesis system. The synthesized UiO-66 samples were characterized by X-ray diffraction (XRD), N₂ adsorption-desorption, scanning electron microscopy (SEM), thermogravimetrical analysis (TGA), temperature-programmed desorption of NH₃(NH₃-TPD). Their catalytic performances were investigated in transesterification of tributyrin and soybean oil with methanol. The results showed that UiO-66 samples with different amounts of defects could be successfully prepared by varying the synthesis temperatures and/or the BDC/Zr ratios used in the synthesis system. The catalytic activities of the UiO-66 materials greatly depended on their linker defects and enhanced with the increase of the defect amount. The UiO-66 was an efficient catalyst for transesterification of tributyrin and soybean oil with methanol under mild reaction conditions and its catalytic activity was comparable to other solid acid catalysts reported in the literatures. The UiO-66 catalyst was relatively stable and could be reused.

Select

Low cost, high performance supercapacitor electrode using coconut wastes: eco-friendly approach

Divyashree A., Shoriya Aruni Bt Abdul Manaf, Yallappa S., Chaitra K., Kathyayini N., Gurumurthy Hegde

2016, 25(5): 880-887. DOI: 10.1016/j.jechem.2016.08.002

摘要 ( 4068 )

Low cost, high performance supercapacitor electrodes were fabricated using coconut waste as precursor. Simple one step pyrolysis is adopted to get the spherical shaped particle where lignocellulosic nature of carbon converts into porous carbon nanospheres. Three types of coconut wastes, namely, coconut fiber (CF), coconut leaves (CL) and coconut stick (CS) have been studied and compared for their application in supercapacitors. Uniform spherical shape with particle size ranging from 30 to 60 nm for leaves and sticks and ～20 nm for fibers was obtained. The electrochemical properties of the porous carbon nanospheres were studied using cyclic voltammetry (CV), chronopotentiometry (CP) and electrochemical impedance spectroscopy (EIS). The porous carbon nanospheres derived from all the three biowaste samples show good electrochemical performance for supercapacitor application. Porous carbon nanospheres derived from coconut fiber exhibited maximum specific capacitance of 236 F/g followed by coconut stick and coconut leaves with 208 and 116 F/g respectively at a scan rate of 2 mV/s. Further impedance studies showed a charge transfer resistance of 4.9Ω for the porous carbon nanospheres derived from coconut fiber, while those from coconut leaves and coconut stick exhibited a slightly higher resistance of 6 and 14.2Ω, respectively. The simple eco-friendly approach we have demonstrated for synthesizing coconut waste based carbon nanospheres makes them excellent candidates for future, low-cost, energy storage devices.

Select

Hydrogen-transfer conversion of furfural into levulinate esters as potential biofuel feedstock

Bingfeng Chen, Fengbo Li, Zhijun Huang, Guoqing Yuan

2016, 25(5): 888-894. DOI: 10.1016/j.jechem.2016.06.007

摘要 ( 4104 )

Furfural is directly converted to levulinate esters (isopropyl levulinate and furan-2-ylmethyl-levulinate) as potential biofuel feedstocks, through a combined catalytic strategy. Nb₂O₅-ZrO₂ mixed oxide microspheres are used as bifunctional catalysts for hydrogen-transfer hydrogenation and acid-catalyzed alcoholysis in isopropanol. Bifunctional catalysts improve sustainability of furfural conversion through process intensification. Hydrogen transfer hydrogenation from isopropanol avoids dangerous hydrogen gas, and abates process and environmental costs. Isopropyl levulinate and furan-2-ylmethyl-levulinate are the main products that can be applied as blending components in biodiesel or hydrocarbon fuels.

过刊目录