? Journal of Energy Chemistry
Journal of Energy Chemistry
ISSN 1003-9953
     
能源化学(英文)

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Nanostructure in Energy Conversion

Tailor-made nanostructured materials can be applied for solving the pressing challenges associated with energy conversion and storage. The review puts different research fields into perspective, namely (photo) thermal synthesis of renewable fuels over heterogeneous catalysts, the fabrication of stable and active electrocatalysts and electrode materials for water splitting, and the direct conversion of sunlight in photovoltaics and photoelectrodes. Differing challenges, but also common benefits associated with applications of nanostructured materials in those different fields are discussed. It will be shown that well-controlled catalytically active sites are often the main challenge, and that a multitude of elementary steps have to be considered.


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2016 Vol.25 No.2, Published: 2016-03-15
Preface | Highlight | REVIEW | Communication | ARTICLES |
 
 
Preface
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Preface to the Special Issue on Nanoconcepts in Energy Chemistry and Catalysis
Dangsheng Su, Gabriele Centi
2016 Vol. 25 (2): 0-0 [Abstract] ( 301 ) [HTML 1KB] [PDF] ( 0 )

The demand for a sustainable development of our society requires a fundamental turn in the current approach to energy production and use, which requires developing new concepts and technologies for catalysis in energy chemistry and environmental protection. Realize this challenge requires new materials, new technologies and new processes that can bring about a revolutionary change in our daily life. The title of this special JEC issue remarks that we need to operate at the nano-scale and introduce new concepts in materials design to change from an evolutionary to a revolutionary change in this area. For this reason, we indicated “Nanoconcepts in Energy Chemistry and Catalysis”, to remark the idea of the need to manipulate the fundamental steps in energy conversion and storage and in catalysis at the level of nanostructured materials and their composite.
This issue collects 22 contributions, including one highlight, four reviews, one communication and 16 full papers covering all the important applications of nanoconcepts in energy chemistry and catalysis. All the papers were written by international leading experts and specialists in the field of energy chemistry and catalysis including electrocatalysis for oxygen reduction reaction, electrode design for battery, nanocatalysts for Fisher-Tropsch synthesis, photocatalyst for hydrogen production, and materials for CO2 capture.
The first paper highlighted the recent work of Bao's group on the direct, non-oxidative conversion of methane to ethylene, aromatics, and hydrogen, an excellent example how nanoconcepts in catalysis can lead to breakthrough in the use of natural gas. The following four reviews, written by international well-known experts in the field, address the application of nanomaterials and ionic liquid in energy conversion and catalysis. These reviews provide a unique opportunity for the readers to be updated on the latest developments and new opportunities offered by using the advanced nanoconcepts discussed in these reviews.
Finally, one communication and 16 full articles report the newest results using nanostructured and materials in a various applications from oxygen reduction reaction, water splitting, hydrogen peroxide production, CO2 capture, as electrode materials and some other energy- and catalysis-related process.
We believe that this special issue dedicated to the use of nanoconcepts in energy chemistry represents a unique opportunity for young and experienced researches in the field of sustainable energy to have an updated view on this exciting topic that we are convinced is an enabling factor for the future of our society. We thus invite all to have this special issue as a privileged component of your bookshelf.

Highlight
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A new horizontal in C1 chemistry: Highly selective conversion of syngas to light olefins by a novel OX-ZEO process
Ye Wang
2016 Vol. 25 (2): 169-170 [Abstract] ( 353 ) [HTML 1KB] [PDF] ( 0 )

The most challenging goal of C1 chemistry is the control of C-C coupling to produce chemicals or fuels from C1 feedstocks, in particular syngas (H2 /CO), which can be derived from various carbon resources such as coal, natural gas or shale gas, and biomass. Light olefins including ethylene, propylene and butenes (C2=-C4=) are important building-block chemicals, which are currently produced from naphtha. The synthesis of light olefins from syngas is a promising alternative. Fischer-Tropsch (FT) synthesis, which has a history of more than 90 years, is currently the major process for the direct conversion of syngas to hydrocarbons including light olefins, but the C2 =-C4= selectivity is limited because of the FT mechanism, which involves the C-C coupling of CHx(x=1-3) intermediates formed via CO dissociation on metal (typically Fe, Co or Ru) surfaces [1]. The C-C coupling on open metal surfaces is uncontrollable, leading to wide distribution of hydrocarbon products following the Anderson-Schulz-Flory (ASF) distribution. The maximum selectivity of C2-C4 hydrocarbons (including paraffins and olefins) is 58% [1]. Light olefins may also be produced from syngas via a two-process route, i.e., methanol synthesis and methanol to olefins (MTO), but this indirect route is water- and energyintensive.

REVIEW
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Nanostructure in energy conversion
Saskia Buller, Jennifer Strunk
2016 Vol. 25 (2): 171-190 [Abstract] ( 314 ) [HTML 1KB] [PDF] ( 0 )

Nanostructured and nanosized materials are widely applied to tackle the pressing challenges associated with energy conversion. In this conceptual review, rather than highlighting separate examples, we aim to give a general overview about where and how nanostructure design can be beneficial in the three major research fields (photo)thermal chemical energy conversion, electrochemical energy conversion, and solar energy conversion. It will be shown that in many cases the design of catalytically active nanostructures is the main task and that especially for catalysts nanostructure and activity are inseparably linked to each other. Moreover, electrochemical and photochemical processes are complicated by the overlap of multiple processes that all need to be optimized, including in particular light absorption, charge migration, recombination and trapping events and surface processes. It will also be shown how the development of materials for new challenges can often be based on our knowledge on existing materials for related applications.

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Microbe-derived carbon materials for electrical energy storage and conversion
Li Wei, H. Enis Karahan, Shengli Zhai, Yang Yuan, Qihui Qian, Kunli Goh, Andrew Keong Ng, Yuan Chen
2016 Vol. 25 (2): 191-198 [Abstract] ( 314 ) [HTML 1KB] [PDF] ( 0 )

Microbes are microscopic living organisms that surround us which include bacteria, archaea, most protozoa, and some fungi and algae. In recent years, microbes have been explored as novel precursors to synthesize carbon-based (nano)materials and as substrates or templates to produce carbon-containing (nano)composites. Being greener and more affordable, microbe-derived carbons (MDCs) offer good potential for energy applications. In this review, we describe the unique advantages of MDCs and outline the common procedures to prepare them. We also extensively discuss the energy applications of MDCs including their use as electrodes in supercapacitors and lithium-ion batteries, and as electrocatalysts for processes such as oxygen reduction, oxygen evolution, and hydrogen evolution reactions which are essential for fuel cell and water electrochemical splitting cells. Based on the literature trend and our group's expertise, we propose potential research directions for developing new types of MDCs. This review, therefore, provides the state-of-the-art of a new energy chemistry concept. We expect to stimulate future research on the applications of MDCs that may address energy and environmental challenges that our societies are facing.

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Ionic liquids in electrocatalysis
Gui-Rong Zhang, Bastian J. M. Etzold
2016 Vol. 25 (2): 199-207 [Abstract] ( 295 ) [HTML 1KB] [PDF] ( 0 )

The performance of an electrocatalyst, which is needed e.g. for key energy conversion reactions such as hydrogen evolution, oxygen reduction or CO2 reduction, is determined not only by the inherent structure of active sites but also by the properties of the interfacial structures at catalytic surfaces. Ionic liquids (ILs), as a unique class of metal salts with melting point below 100℃, present themselves as ideal modulators for manipulations of the interfacial structures. Due to their excellent properties such as good chemical stability, high ionic conductivity, wide electrochemical windows and tunable solvent properties the performance of electrocatalysts can be substantially improved through ILs. In the current minireview, we highlight the critical role of the IL phase at the microenvironments created by the IL, the liquid electrolyte, catalytic nanoparticles and/or support materials, by detailing the promotional effect of IL in electrocatalysis as reaction media, binders, and surface modifiers. Updated exemplary applications of IL in electrocatalysis are given and moreover, the latest developments of IL modified electrocatalysts following the "Solid Catalyst with Ionic Liquid Layer (SCILL)" concept are presented.

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Transformation of bio-derived acids into fuel-like alkanes via ketonic decarboxylation and hydrodeoxygenation: Design of multifunctional catalyst, kinetic and mechanistic aspects
Irina L. Simakova, Dmitry Yu. Murzin
2016 Vol. 25 (2): 208-224 [Abstract] ( 343 ) [HTML 1KB] [PDF] ( 0 )

The combination of a low cost source of Biofine's levulinic acid with available way of valeric acid synthesis opens up new opportunities for valeric acid as a promising bio-derived source for synthesis of valuable compounds for transportation sector. The present review illustrates the development of different approaches to one-pot synthesis of fuel-like alkanes from lignocellulose derived carboxylic acids where particular focus is given to valeric acid consecutive decarboxylative coupling (ketonization) and ketone hydrodeoxygenation in a single reactor over one catalyst bed. The key factors that influence the catalytic performance on both ketonization and hydrodeoxygenation steps as well as their cross-influence will be clarified to provide insights for the design of more efficient catalysts for the one-pot transformation. Valeric acid is considered as a potential acid source from viewpoint of cost effectiveness and feasibility of such transformation with reasonable alkane yield. The both reaction mechanisms and kinetics will also be discussed to understand deeply how the selective C-C coupling and following C = O hydrogenation can be achieved.

Communication
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A nano-engineered graphene/carbon nitride hybrid for photocatalytic hydrogen evolution
Xiaobo Li, Yao Zheng, Anthony F. Masters, Thomas Maschmeyer
2016 Vol. 25 (2): 225-227 [Abstract] ( 277 ) [HTML 1KB] [PDF] ( 0 )

A metal-free photocatalytic hydrogen evolution system was successfully fabricated using heteroatom doped graphene materials as electron-transfer co-catalysts and carbon nitride as a semiconductor. The catalytic role of graphene is significantly dependent on the heteroatom dopant of the graphene, such as O, S, B, N doped/undoped graphene co-catalysts, and N-graphene shows the best catalytic hydrogen evolution rate.

ARTICLES
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Bio-inspired carbon electro-catalysts for the oxygen reduction reaction
Kathrin Preuss, Vasanth Kumar Kannuchamy, Adam Marinovic, Mark Isaacs, Karen Wilson, Isaac Abrahams, Maria-Magdalena Titirici
2016 Vol. 25 (2): 228-235 [Abstract] ( 318 ) [HTML 1KB] [PDF] ( 0 )

We report the synthesis, characterisation and catalytic performance of two nature-inspired biomassderived electro-catalysts for the oxygen reduction reaction in fuel cells. The catalysts were prepared via pyrolysis of a real food waste (lobster shells) or by mimicking the composition of lobster shells using chitin and CaCO3 particles followed by acid washing. The simplified model of artificial lobster was prepared for better reproducibility. The calcium carbonate in both samples acts as a pore agent, creating increased surface area and pore volume, though considerably higher in artificial lobster samples due to the better homogeneity of the components. Various characterisation techniques revealed the presence of a considerable amount of hydroxyapatite left in the real lobster samples after acid washing and a low content of carbon (23%), nitrogen and sulphur (< 1%), limiting the surface area to 23 m2/g, and consequently resulting in rather poor catalytic activity. However, artificial lobster samples, with a surface area of ≈200 m2/g and a nitrogen doping of 2%, showed a promising onset potential, very similar to a commercially available platinum catalyst, with better methanol tolerance, though with lower stability in long time testing over 10,000 s.

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S-doped carbon aerogels/GO composites as oxygen reduction catalysts
Mykola Seredych, Krisztina László, Enrique Rodríguez-Castellón, Teresa J. Bandosz
2016 Vol. 25 (2): 236-245 [Abstract] ( 252 ) [HTML 1KB] [PDF] ( 0 )

Composites of carbon aerogel and graphite oxide (GO) were synthesized using a self-assembly method based on dispersive forces. Their surface was modified by treatment in hydrogen sulfide at 650 and 800℃. The samples obtained were characterized by adsorption of nitrogen, TA-MS, XPS, potentiometric titration, and HRTEM and tested as catalysts for oxygen reduction reactions (ORR) in an alkaline medium. The synergistic effect of the composite (electrical conductivity, porosity and surface chemistry) leads to a good ORR catalytic activity. The onset potential for the composite of carbon aerogel heated at 800℃ is shifted to a more positive value and the number of electron transfer was 2e- at the potential 0.68 V versus RHE and it increased to 4e- with an increase in the negative values of the potential. An excellent tolerance to methanol crossover was also recorded.

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Water oxidation electrocatalysis with iron oxide nanoparticles prepared via laser ablation
Erica Pizzolato, Stefano Scaramuzza, Francesco Carraro, Alessia Sartori, Stefano Agnoli, Vincenzo Amendola, Marcella Bonchio, Andrea Sartorel
2016 Vol. 25 (2): 246-250 [Abstract] ( 262 ) [HTML 1KB] [PDF] ( 0 )

Iron oxide nanoparticles (FeOx NPs, 5-30 nm size) prepared via laser ablation in liquid were supported onto Indium Tin Oxide conductive glass slides by magnetophoretic deposition (MD) technique. The resulting FeOx@ITO electrodes are characterized by a low amount of iron coverage of 16-50 nmol/cm2, and show electrocatalytic activity towards water oxidation in neutral phosphate buffer pH 7 with 0.58 V overpotential and quantitative Faradaic efficiency towards oxygen production. XPS analysis on the oxygen region of the FeOx films reveals a substantial hydration of the surface after catalysis, recognized as a crucial step to access reactivity.

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Electrocatalytic hydrogen peroxide formation on mesoporous non-metal nitrogen-doped carbon catalyst
Frédéric Hasché, Mehtap Oezaslan, Peter Strasser, Tim-Patrick Fellinger
2016 Vol. 25 (2): 251-257 [Abstract] ( 300 ) [HTML 1KB] [PDF] ( 0 )

Direct electrochemical formation of hydrogen peroxide (H2O2) from pure O2 and H2 on cheap metal-free earth abundant catalysts has emerged as the highest atom-efficient and environmentally friendly reaction pathway and is therefore of great interest from an academic and industrial point of view. Very recently, novel metal-free mesoporous nitrogen-doped carbon catalysts have attracted large attention due to the unique reactivity and selectivity for the electrochemical hydrogen peroxide formation [1-3]. In this work, we provide deeper insights into the electrocatalytic activity, selectivity and durability of novel metal-free mesoporous nitrogen-doped carbon catalyst for the peroxide formation with a particular emphasis on the influence of experimental reaction parameters such as pH value and electrode potential for three different electrolytes. We used two independent approaches for the investigation of electrochemical hydrogen peroxide formation, namely rotating ring-disk electrode (RRDE) technique and photometric UV-VIS technique. Our electrochemical and photometric results clearly revealed a considerable peroxide formation activity as well as high catalyst durability for the metal-free nitrogen-doped carbon catalyst material in both acidic as well as neutral medium at the same electrode potential under ambient temperature and pressure. In addition, the obtained electrochemical reactivity and selectivity indicate that the mechanisms for the electrochemical formation and decomposition of peroxide are strongly dependent on the pH value and electrode potential.

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Atomic layer deposition of ultrathin layered TiO2 on Pt/C cathode catalyst for extended durability in polymer electrolyte fuel cells
Sangho Chung, Myounghoon Choun, Beomgyun Jeong, Jae Kwang Lee, Jaeyoung Lee
2016 Vol. 25 (2): 258-264 [Abstract] ( 272 ) [HTML 1KB] [PDF] ( 0 )

This study shows the preparation of a TiO2 coated Pt/C (TiO2/Pt/C) by atomic layer deposition (ALD), and the examination of the possibility for TiO2/Pt/C to be used as a durable cathode catalyst in polymer electrolyte fuel cells (PEFCs). Cyclic voltammetry results revealed that TiO2/Pt/C catalyst which has 2 nm protective layer showed similar activity for the oxygen reduction reaction compared to Pt/C catalysts and they also had good durability. TiO2/Pt/C prepared by 10 ALD cycles degraded 70% after 20 0 0 Accelerated degradation test, while Pt/C corroded 92% in the same conditions. TiO2 ultrathin layer by ALD is able to achieve a good balance between the durability and activity, leading to TiO2/Pt/C as a promising cathode catalyst for PEFCs. The mechanism of the TiO2 protective layer used to prevent the degradation of Pt/C is discussed.

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Carbon nanotubes as conducting support for potential Mn-oxide electrocatalysts: Influences of pre-treatment procedures
Saskia Buller, Marius Heise-Podleska, Norbert Pfänder, Marc Willinger, Robert Schlögl
2016 Vol. 25 (2): 265-271 [Abstract] ( 271 ) [HTML 1KB] [PDF] ( 0 )

Different oxygen and nitrogen containing functional groups were created on the surface of the multiwalled carbon nanotubes. The multi-walled carbon nanotubes were treated in ultrasonic bath with sulfuric or nitric acid. Furthermore the surface texture was modified by increase of the roughness. In particular after treatment with the oxidizing nitric acid, in comparison to the H2SO4 or ultra-sonic treated samples, craters and edges are dominating the surface structures. Manganese oxide was deposited on the multiwalled carbon nanotubes by precipitation mechanism. Various manganese oxides are formed during the deposition process. The samples were characterized by elemental analysis, microscopy, thermal analysis, Raman spectroscopy, and by the zeta potential as well as X-ray diffraction measurements. It was shown that the deposited manganese oxides are stabilized rather by surface texture of the multi-walled carbon nanotubes than by created functional groups.

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Design of Fe3-xO4 raspberry decorated graphene nanocomposites with high performances in lithium-ion battery
Olivier Gerber, Sylvie Bégin-Colin, Benoit P. Pichon, Elodie Barraud, Sébastien Lemonnier, Cuong Pham-Huu, Barbara Daffos, Patrice Simon, Jeremy Come, Dominique Bégin
2016 Vol. 25 (2): 272-277 [Abstract] ( 229 ) [HTML 1KB] [PDF] ( 0 )

Fe3-xO4 raspberry shaped nanostructures/graphene nanocomposites were synthesized by a one-step polyol-solvothermal method to be tested as electrode materials for Li-ion battery (LIB). Indeed, Fe3-xO4 raspberry shaped nanostructures consist of original oriented aggregates of Fe3-xO4 magnetite nanocrystals, ensuring a low oxidation state of magnetite and a hollow and porous structure, which has been easily combined with graphene sheets. The resulting nanocomposite powder displays a very homogeneous spatial distribution of Fe3-xO4 nanostructures at the surface of the graphene sheets. These original nanostructures and their strong interaction with the graphene sheets resulted in very small capacity fading upon Li+ ion intercalation. Reversible capacity, as high as 660 mAh/g, makes this material promising for anode in Li-ion batteries application.

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Synthesis-structure correlations of manganese-cobalt mixed metal oxide nanoparticles
Manuel Gliech, Arno Bergmann, Camillo Spöri, Peter Strasser
2016 Vol. 25 (2): 278-281 [Abstract] ( 271 ) [HTML 1KB] [PDF] ( 0 )

Mixed metal oxides in the nanoscale are of great interest for many aspects of energy related research topics as water splitting, fuel cells and battery technology. The development of scalable, cost-efficient and robust synthetic routes toward well-defined solid state structures is a major objective in this field. While monometallic oxides have been studied in much detail, reliable synthetic recipes targeting specific crystal structures of mixed metal oxide nanoparticles are largely missing. Yet, in order to meet the requirements for a broad range of technical implementation it is necessary to tailor the properties of mixed metal oxides to the particular purpose. Here, we present a study on the impact of the nature of the gas environment on the resulting crystal structure during a post-synthesis thermal heat treatment of manganese-cobalt oxide nanoparticles. We monitor the evolution of the crystal phase structure as the gas atmosphere is altered from pure nitrogen to synthetic air and pure oxygen. The particle size and homogeneity of the resulting nanoparticles increase with oxygen content, while the crystal structure gradually changes from rocksalt-like to pure spinel. We find the composition of the particles to be independent of the gas atmosphere. The manganese-cobalt oxide nanoparticles exhibited promising electrocatalytic activity regarding oxygen evolution in alkaline electrolyte. These findings offer new synthesis pathways for the direct preparation of versatile utilizable mixed metal oxides.

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Promoting effect of nitrogen doping on carbon nanotub e-supporte d RuO2 applied in the electrocatalytic oxygen evolution reaction
Kunpeng Xie, Wei Xia, Justus Masa, Fengkai Yang, Philipp Weide, Wolfgang Schuhmann, Martin Muhler
2016 Vol. 25 (2): 282-288 [Abstract] ( 273 ) [HTML 1KB] [PDF] ( 0 )

RuO2 nanoparticles supported on multi-walled carbon nanotubes (CNTs) functionalized with oxygen (OCNTs) and nitrogen (NCNTs) were employed for the oxygen evolution reaction (OER) in 0.1 M KOH. The catalysts were synthesized by metal-organic chemical vapor deposition using ruthenium carbonyl (Ru3(CO)12 ) as Ru precursor. The obtained RuO2/OCNT and RuO2/NCNT composites were characterized using TEM, H2-TPR, XRD and XPS in order probe structure-activity correlations, particularly, the effect of the different surface functional groups on the electrochemical OER performance. The electrocatalytic activity and stability of the catalysts with mean RuO2 particle sizes of 13-14 nm was evaluated by linear sweep voltammetry, cyclic voltammetry, and chronopotentiometry, showing that the generation of nitrogen-containing functional groups on CNTs was beneficial for both OER activity and stability. In the presence of RuO2, carbon corrosion was found to be significantly less severe.

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Effect of initial nickel particle size on stability of nickel catalysts for aqueous phase reforming
Tomas van Haasterecht, Marten Swart, Krijn P. de Jong, Johannes Hendrik Bitter
2016 Vol. 25 (2): 289-296 [Abstract] ( 244 ) [HTML 1KB] [PDF] ( 0 )

The deactivation behavior by crystallite growth of nickel nanoparticles on various supports (carbon nanofibers, zirconia, SiC, α-Al2O3 and γ-Al2O3 ) was investigated in the aqueous phase reforming of ethylene glycol. Supported Ni catalysts of ~10 wt% were prepared by impregnation of carbon nanofibers (CNF), ZrO2, SiC, γ-Al2O3 and α-Al2O3. The extent of the Ni nanoparticle growth on various support materials follows the order CNF ~ ZrO2 > SiC > γ-Al2O3 >> α-Al2O3 which sequence, however, was determined by the initial Ni particle size. Based on the observed nickel leaching and the specific growth characteristics; the particle size distribution and the effect of loading on the growth rate, Ostwald ripening is suggested to be the main mechanism contributing to nickel particle growth. Remarkably, initially smaller Ni particles (~12 nm) supported on α-Al2O3 were found to outgrow Ni particles with initially larger size (~20 nm). It is put forward that the higher susceptibility with respect to oxidation of the smaller Ni nanoparticles and differences in initial particle size distribution are responsible for this behavior.

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Role of size and pretreatment of Pd particles on their behaviour in the direct synthesis of H2O2
Salvatore Abate, Katia Barbera, Gabriele Centi, Gianfranco Giorgianni, Siglinda Perathoner
2016 Vol. 25 (2): 297-305 [Abstract] ( 233 ) [HTML 1KB] [PDF] ( 0 )

Two families of catalysts, based on Pd nanoparticles supported on ceramic asymmetric tubular alumina membranes, are studies in the direct synthesis of H2O2. They are prepared by depositing Pd in two ways: (i) reduction with N 2 H 4 in an ultrasonic bath and (ii) by impregnation-deposition. The first preparation leads to larger particles, with average size of around 11 nm, while the second preparation leads to smaller particles, with average size around 4 nm. The catalytic membranes were tested as prepared, after thermal treatment in air and after further pre-reduction with H2 in mild (100℃) conditions. Samples were characterized by TEM, CO-chemisorption monitored by DRIFTS method and TPR, while catalytic tests have been performed in a semi-batch recirculation membrane reactor. Experimental catalytic results were analysed using two kinetics models to derive the reaction constants for the parallel and consecutive reactions of the kinetic network. Smaller particles of Pd show lower selectivity due to the higher rate of parallel combustion, even if the better dispersion of Pd and thus higher metal surface area in the sample lead to a productivity in H2O2similar or even higher than the sample with the larger Pd particles. Independently on the presence of smaller or larger Pd nanoparticles, an oxidation treatment leads to a significant enhancement in the productivity, although the catalyst progressively reduces during the catalytic process. The inhibition of the parallel combustion reaction (to water) induced from the calcination treatment remains after the in-situ reduction of the oxidized Pd species formed during the pre-treatment. This is likely due to the elimination of defect sites which dissociatively activate oxygen, and tentatively attributed to Pd sites able to give three-and four-fold coordination of CO.

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Selective synthesis of carbon monoxide via formates in reverse water-gas shift reaction over alumina-supported gold catalyst
Nobuhiro Ishito, Kenji Hara, Kiyotaka Nakajima, Atsushi Fukuoka
2016 Vol. 25 (2): 306-310 [Abstract] ( 246 ) [HTML 1KB] [PDF] ( 0 )

Thermal decomposition of formic acid on SiO2, CeO2 and γ-Al2O3 was studied as an elementary step of reverse water-gas shit reaction (RWGS) over supported Au catalysts. γ-Al2O3 showed the highest CO selectivity among the tested oxides in the decomposition of formic acid. Infrared spectroscopy showed the formation of four formate species on γ-Al2O3 : three η1-type and one μ2-type species, and these formates decomposed to CO at 473 K or higher. Au-loaded γ-Al2O3 samples were prepared by a depositionprecipitation method and used as catalysts for RWGS. The supported Au catalyst gave CO with high selectivity over 99% from CO2 and H2, which is attributed to the formation of formates on Au and subsequent decomposition to CO on γ-Al2O3.

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Fabrication of K-promoted iron/carbon nanotubes composite catalysts for the Fischer-Tropsch synthesis of lower olefins
Xuezhi Duan, Di Wang, Gang Qian, John C. Walmsley, Anders Holmen, De Chen, Xinggui Zhou
2016 Vol. 25 (2): 311-317 [Abstract] ( 264 ) [HTML 1KB] [PDF] ( 0 )

K-promoted iron/carbon nanotubes composite (i.e., FeK-OX) was prepared by a redox reaction between carbon nanotubes and K2FeO4 followed by thermal treatments on a purpose as the Fischer-Tropsch catalyst for the direct conversion of syngas to lower olefins. Its catalytic behaviors were compared with those of the other two Fe-IM and FeK-IM catalysts prepared by impregnation method followed by thermal treatments. The novel FeK-OX composite catalyst is found to exhibit higher hydrocarbon selectivity, lower olefins selectivity and chain growth probability as well as better stability. The catalyst structureperformance relationship has been established using multiple techniques including XRD, Raman, TEM and EDS elemental mapping. In addition, effects of additional potassium into the FeK-OX composite catalyst on the FTO performance were also investigated and discussed. Additional potassium promoters further endow the catalysts with higher yield of lower olefins. These results demonstrated that the introduction method of promoters and iron species plays a crucial role in the design and fabrication of highly active, selective and stable iron-based composite catalysts for the FTO reaction.

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Tuning of textural properties of germanosilicate zeolites ITH and IWW by acidic leaching
Valeryia I. Kasneryk, Mariya V. Shamzhy, Maksym V. Opanasenko, Jiří Čejka
2016 Vol. 25 (2): 318-326 [Abstract] ( 290 ) [HTML 1KB] [PDF] ( 0 )

The possibility to adjust textural properties of ITH and IWW zeolites by the variation of conditions (e.g. temperature, pH, duration) of acidic leaching was shown. While the growth of the temperature of acid treatment caused the increasing amount of leached Ge atoms and enhancing volumes of both micro and mesopores at 80℃, the mesopore volume in ITH (Si/Ge = 3.4 and 5.8) and IWW (Si/Ge = 3.3) zeolites changed with the duration of the treatment (pH = 2; T= 80℃) as follows: 96 h < 1 h < 24 h. Independently on the chemical composition and zeolite topology, the treatment of germanosilicate zeolites at pH = 2-7 resulted in development of both micro and mesoporosity accompanied by the extraction of substantial amount of Ge atoms, while the increasing acidity up to pH = 0 resulted in some reduction of Ge extraction and in the development of mesopores at maintained value of micropore volume when compared with initial germanosilicates. The higher activity (i.e. number of reactant molecules converted per active site) of germanosilicate with modified micro-mesoporous channel system in comparison with parent IWW zeolite in esterification of levulinic acid was attributed to enhanced accessibility of active sites.

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Impact of solvents and surfactants on the self-assembly of nanostructured amine functionalized silica spheres for CO2 capture
Edith Berger, Maximilian W. Hahn, Thomas Przybilla, Benjamin Winter, Erdmann Spiecker, Andreas Jentys, Johannes A. Lercher
2016 Vol. 25 (2): 327-335 [Abstract] ( 250 ) [HTML 1KB] [PDF] ( 0 )

Macroscopic SiO2 spheres with a homogeneous amine distribution were synthesized by a one-step emulsion based synthesis approach in a flow column reactor. The CO2 adsorption capacity of the nanostructured amine-functionalized silica spheres was studied in absence and presence of H2O. The structural properties were adjusted by varying solvents and surfactants during the synthesis and, at constant amine loadings, were found to be the main factor for influencing the CO2 sorption capacities. Under water-free conditions CO2 is bound to the amino groups via the formation of carbamates, which require two neighboring amino groups to adsorb one CO2 molecule. At constant amine concentrations sorbents with lower surface area allow to establish a higher amine density on the surface, which enhances the CO2 uptake capacities under dry conditions. In presence of H2O the CO2 adsorption changes to 1:1 stoichiometry due to stabilization of carbamates by protonation of H2O and formation of further species such as bicarbonates, which should in principle double the adsorption capacities. Low concentrations of physisorbed H2O (0.3 mmol/g) did not impair the adsorption capacity of the adsorbents for CO2, while at higher water uptakes (0.6 and 1.1 mmol/g) the CO2 uptake is reduced, which could be attributed to capillary condensation of H2O or formation of bulky reaction products blocking inner pores and access to active sites.

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Novel layer-by-layer assembly of rGO-hybridised ZnO sandwich thin films for the improvement of photo-catalysed hydrogen production
Swe Jyan Teh, Chin Wei Lai, Sharifah Bee Abd. Hamid
2016 Vol. 25 (2): 336-344 [Abstract] ( 267 ) [HTML 1KB] [PDF] ( 0 )

Metal oxide semiconductor materials such as ZnO have tremendous potential as light absorbers for photocatalysed electrodes in the electrochemical reduction of water. Promoters such as rGO have been added to reduce the recombination losses of charge carriers and improve its photoelectrochemical activity. In this study, the effect of layer ordering on the charge transfer properties of rGO-hybridised ZnO sandwich thin films for the photo-catalysed electrochemical reduction of water was investigated. rGO-hybridised ZnO sandwich thin films were prepared via a facile electrode position technique using a layer-by-layer approach. The thin films were analysed using FESEM, XRD, Raman, PL, UV-vis, EIS and CV techniques to investigate its morphological, optical and electrochemical properties. The FESEM images show the formation of distinct layers of rGO and ZnO nanorods/flakes via the layer-by-layer method. XRD confirmed the wurtzite structure of ZnO. PL spectroscopy revealed a reduction of photoemission intensity in the visible region (580 nm) when rGO was incorporated into the ZnO thin film. Among the six thin films prepared, ZnO/rGO showed superior performance compared to the other thin films (0.964 mA/cm) due to the presence of graphene edges which participate as heterogenous electrocatalysts in the photocatalysed electrolysis of water. rGO also acts as electron acceptor, forming an n-p heterojunction which improves the activity of ZnO to oxidise water molecules to O2. EIS revealed that the application of rGO as back contact (rGO/ZnO, rGO/ZnO/rGO) reduces the charge transfer resistance of a semiconductor thin film. Alternatively, rGO as front contact (ZnO/rGO, rGO/ZnO/rGO) improves the photo-catalysed electrolysis of water through the participation of the rGO edges in the chemical activation of water. The findings from this study indicate that the layer ordering significantly affects the thin film's electrostatic properties and this understanding can be further advantageous for tunable applications.

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Bimonthly
(Started in 1992)
Renamed from JNGC in 2013

ISSN 2095-4956
CN 21-1585/O4

Editors-in-Chief
Xinhe Bao
Gabriele Centi


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Editorial Office of
Journal of Energy Chemistry

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Chemical Physics, CAS
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