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Nanoscopic gold particles have gained very high interest because of their promising catalytic activity for various chemicals reactions. Among these reactions, low-temperature CO oxidation is the most extensively studied one due to its... more
Nanoscopic gold particles have gained very high interest because of their promising catalytic activity for various chemicals reactions. Among these reactions, low-temperature CO oxidation is the most extensively studied one due to its practical relevance in environmental applications and the fundamental problems associated with its very high activity at low temperatures. Gold nanoparticles supported on manganese oxide belong to the most active gold catalysts for CO oxidation. Among a variety of manganese oxides, Mn2O3 is considered to be the most favorable support for gold nanoparticles with respect to catalytic activity. Gold on MnO2 has been shown to be significantly less active than gold on Mn2O3 in previous work. In contrast to these previous studies, in a comprehensive study of gold nanoparticles on different manganese oxides, we developed a gold catalyst on MnO2 nanostructures with extremely high activity. Nano-sized gold particles (2-3 nm) were supported on α-MnO2 nanowires a...
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Co3O4 with a spinel structure is a very active oxide catalyst for the oxidation of CO. In such catalysts, octahedrally coordinated Co(3+) is considered to be the active site, while tetrahedrally coordinated Co(2+) is assumed to be... more
Co3O4 with a spinel structure is a very active oxide catalyst for the oxidation of CO. In such catalysts, octahedrally coordinated Co(3+) is considered to be the active site, while tetrahedrally coordinated Co(2+) is assumed to be basically inactive. In this study, a highly ordered mesoporous CoO has been prepared by H2 reduction of nanocast Co3O4 at low temperature (250 °C). The as-prepared CoO material, which has a rock-salt structure with a single Co(2+) octahedrally coordinated by lattice oxygen in Fm3̅m symmetry, exhibited unexpectedly high activity for CO oxidation. Careful investigation of the catalytic behavior of mesoporous CoO catalyst led to the conclusion that the oxidation of surface Co(2+) to Co(3+) causes the high activity. Other mesoporous spinels (CuCo2O4, CoCr2O4, and CoFe2O4) with different Co species substituted with non/low-active metal ions were also synthesized to investigate the catalytically active site of cobalt-based catalysts. The results show that not on...
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The present invention relates to the use of mesoporous graphite particles having a load of sintering stability of the metal nano-particles for a fuel cell, and a further electrochemical applications as a component of the layer in the... more
The present invention relates to the use of mesoporous graphite particles having a load of sintering stability of the metal nano-particles for a fuel cell, and a further electrochemical applications as a component of the layer in the example fuel cell and the storage battery electrodes.
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A simple and scalable method for synthesizing Co3 O4 nanoparticles supported on the framework of mesoporous carbon (MC) was developed. Benefiting from an ion-exchange process during the preparation, the cobalt precursor is introduced into... more
A simple and scalable method for synthesizing Co3 O4 nanoparticles supported on the framework of mesoporous carbon (MC) was developed. Benefiting from an ion-exchange process during the preparation, the cobalt precursor is introduced into a mesostructured polymer framework that results in Co3 O4 nanoparticles (ca. 3 nm) supported on MC (Co3 O4 /MC) with narrow particle size distribution and homogeneous dispersion after simple reduction/pyrolysis and mild oxidation steps. The as-obtained Co3 O4 /MC is a highly efficient catalyst for transfer hydrogenation of α,β-unsaturated aldehydes. Selectivities towards unsaturated alcohols are always higher than 95 % at full conversion. In addition, the Co3 O4 /MC shows high stability under the reaction conditions, it can be recycled at least six times without loss of activity.
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About 15 years ago, the Ryoo group described the synthesis of CMK-5, a material consisting of a hexagonal arrangement of carbon nanotubes. Extension of the surface casting synthesis to oxide compositions, however, was not possible so far,... more
About 15 years ago, the Ryoo group described the synthesis of CMK-5, a material consisting of a hexagonal arrangement of carbon nanotubes. Extension of the surface casting synthesis to oxide compositions, however, was not possible so far, in spite of many attempts. Here it is demonstrated, that crystalline mesoporous hollow zirconia materials with very high surface areas up to 400 m(2) g(-1) , and in selected cases in the form of CMK-5-like, are indeed accessible via such a surface casting process. The key for the successful synthesis is an increased interaction between the silica hard template surface and the zirconia precursor species by using silanol group-rich mesoporous silica as a hard template. The surface areas of the obtained zirconias exceed those of conventionally hard-templated ones by a factor of two to three. The surface casting process seems to be applicable also to other oxide materials.
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Medium well done : Second-generation protic ionic liquids (PILs) and deep eutectic solvents (DESs) have emerged in the last decade as environmentally attractive reaction media for biocatalytic processes. These solvents are of particular... more
Medium well done : Second-generation protic ionic liquids (PILs) and deep eutectic solvents (DESs) have emerged in the last decade as environmentally attractive reaction media for biocatalytic processes. These solvents are of particular interest as reaction media for biocatalytic conversions of substrates that have limited solubility in common organic solvents, such as carbohydrates, nucleosides, steroids, and polysaccharides. Chem. Eur. J. DOI: 10.1002/chem.201601940
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ABSTRACT Mesoporous peapod-like Co3O4@carbon nanotube (CNT) arrays with Co3O4 nanoparticles confined exclusively in the intratubular pores are achieved starting with the preparation of mesoporous SiO2 (SBA-15 hard template) which is... more
ABSTRACT Mesoporous peapod-like Co3O4@carbon nanotube (CNT) arrays with Co3O4 nanoparticles confined exclusively in the intratubular pores are achieved starting with the preparation of mesoporous SiO2 (SBA-15 hard template) which is infiltrated by a furfuryl alcohol-containing polymer solution prior to thermal degradation.
Transition metal oxides are regarded as promising anode materials for lithium-ion batteries because of their high theoretical capacities compared with commercial graphite. Unfortunately, the implementation of such novel anodes is hampered... more
Transition metal oxides are regarded as promising anode materials for lithium-ion batteries because of their high theoretical capacities compared with commercial graphite. Unfortunately, the implementation of such novel anodes is hampered by their large volume changes during the Li(+) insertion and extraction process and their low electric conductivities. Herein, we report a specifically designed anode architecture to overcome such problems, that is, mesoporous peapod-like Co3 O4 @carbon nanotube arrays, which are constructed through a controllable nanocasting process. Co3 O4 nanoparticles are confined exclusively in the intratubular pores of the nanotube arrays. The pores between the nanotubes are open, and thus render the Co3 O4 nanoparticles accessible for effective electrolyte diffusion. Moreover, the carbon nanotubes act as a conductive network. As a result, the peapod-like Co3 O4 @carbon nanotube electrode shows a high specific capacity, excellent rate capacity, and very good ...
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Herein, we present a straightforward surface modification technique for PDMS-based microfluidic devices. The method takes advantage of the high reactivity of concentrated sulfuric acid to enhance the surface properties of PDMS bulk... more
Herein, we present a straightforward surface modification technique for PDMS-based microfluidic devices. The method takes advantage of the high reactivity of concentrated sulfuric acid to enhance the surface properties of PDMS bulk material. This results in alteration of the surface morphology and chemical composition that is in-depth characterized by ATR-FTIR, EDX, SEM, and XPS. In comparison to untreated PDMS, modified substrates exhibit a significantly reduced diffusive uptake of small organic molecules while retaining its low electroosmotic properties. This was demonstrated by exposing the channels of a microfluidic device to concentrated rhodamine B solution followed by fluorescence microscopy. The surface modification procedure was used to improve chip-based electrophoretic separations. Separation efficiencies of FITC-labeled amines/amino acids obtained in treated and untreated PDMS-devices as well as in glass chips were compared. We obtained higher efficiencies in H2 SO4 trea...
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A capillary deposition method for the preparation of opal and inverse opal films has been developed. By this method, one can control the film thickness and the crack arrangement in opal as well as inverse opal structures. This method... more
A capillary deposition method for the preparation of opal and inverse opal films has been developed. By this method, one can control the film thickness and the crack arrangement in opal as well as inverse opal structures. This method combines tube capillarity with cell capillarity or with gravity depending on the stability of the suspensions. The combination of tube capillarity with cell capillarity is used to prepare opal films from stable suspensions. The tube capillary transports the suspension, while the cell capillary helps to assemble the spheres. The setup defines the drying fronts, thickness, and crack arrangements of the opal films. The combination of capillarity with gravity is useful for making opal films from unstable suspensions. Opal films of spheres with size up to 1 mum can be easily prepared from this combination. Here, the gravity influences the arrangement of the spheres. The two-capillary setup has also been used to infiltrate the opal films with a titania precursor. After calcination, inverse titania opal films with skeleton structure have been obtained.
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Layer-by-layer polyelectrolyte multilayer thin films, composed of poly (allylamine hydrochloride)(PAH) and poly (acrylic acid)(PAA) were used as polymeric nanoreactors for the nucleation and growth of Ag-nanoparticles. The effects of... more
Layer-by-layer polyelectrolyte multilayer thin films, composed of poly (allylamine hydrochloride)(PAH) and poly (acrylic acid)(PAA) were used as polymeric nanoreactors for the nucleation and growth of Ag-nanoparticles. The effects of precursor conditions like the ...
Research Interests: Materials Engineering, Condensed Matter Physics, Nanoparticles, Thin Films, X Rays, and 12 moreSurface Coatings, Thin Film, Nanostructures, Nanostructure, Nucleation and Growth, Surface and Coatings Technology, XANES, Size Distribution, Layer by Layer, Metal ion, Nanostructured Material, and Poly Acrylic Acid
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ABSTRACT Mesoporous copper–alumina (Cu–Al2O3) with different copper contents was synthesized in a one-pot reaction via the evaporation-induced self-assembly of Pluronic P123 and the corresponding metal precursors in ethanolic solution in... more
ABSTRACT Mesoporous copper–alumina (Cu–Al2O3) with different copper contents was synthesized in a one-pot reaction via the evaporation-induced self-assembly of Pluronic P123 and the corresponding metal precursors in ethanolic solution in the presence of nitric acid. Mesoporous Cu–Al2O3 calcined at 400 °C exhibits a large BET surface area of 265 m2/g and a pore volume of 0.48 cm3/g. XRD results indicate that the wall of mesoporous Cu–Al2O3 calcined at 400 °C is amorphous, and that it is transformed to crystalline material by further thermal treatment at 800 °C. Copper was formed as very small particles in the composite under 5% H2 flow at high temperature. Moreover, the mesoporous structure did not collapse after the sample was reduced at 650 °C for 4 h, and the copper particles with sizes of around 6 nm were well distributed through the entire mesoporous γ-Al2O3 network. Using the mesoporous Cu/γ-Al2O3 as a bifunctional catalyst for one-step dimethyl ether synthesis from synthesis gas, a CO conversion of 72% and a DME selectivity of 69% were obtained at 50 bar and 310 °C.
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The colloidal deposition method was used to prepare Au/Mg(OH)(2) (0.7 wt % gold) catalysts with gold particle sizes between 1.5 to 5 nm which exhibited very high activity for CO oxidation with specific rates higher than 3.7 mol(CO) x... more
The colloidal deposition method was used to prepare Au/Mg(OH)(2) (0.7 wt % gold) catalysts with gold particle sizes between 1.5 to 5 nm which exhibited very high activity for CO oxidation with specific rates higher than 3.7 mol(CO) x h(-1) x g(Au)(-1) even at temperatures as low as -89 degrees C.
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ABSTRACT
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ABSTRACT The search for more stable electrocatalyst materials for electrochemical energy conversion requires a fundamental understanding of the underlying degradation processes. Advanced characterization techniques like identical location... more
ABSTRACT The search for more stable electrocatalyst materials for electrochemical energy conversion requires a fundamental understanding of the underlying degradation processes. Advanced characterization techniques like identical location transmission electron microscopy (IL-TEM) can provide invaluable insight into the stability of electrode materials on the nanoscale. In this review, the basic principles and the methodology of IL-TEM are described, and its capabilities are revealed by demonstrating the recent progress that has been achieved in research on the stability of fuel cell catalysts. Moreover, we provide future perspectives of the identical location approach towards implementing other electron microscopic and tomographic applications, which will help us to gain an even broader view of the degradation of electrocatalysts.
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... J. Bongard, and Frank Marlow*. Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, 45470 Mülheim an der Ruhr, Germany. Chem. Mater. ... Jeremy W. Galusha, Chia-Kuang Tsung, Galen D. Stucky and Michael H. Bartl. Chemistry... more
... J. Bongard, and Frank Marlow*. Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, 45470 Mülheim an der Ruhr, Germany. Chem. Mater. ... Jeremy W. Galusha, Chia-Kuang Tsung, Galen D. Stucky and Michael H. Bartl. Chemistry of Materials 2008 20 (15), 4925-4930 ...
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ABSTRACT The nanocomposite Co3O4/CoFe2O4 heterostructured mesoporous material was produced via a simple solid–solid reaction of an iron precursor with ordered mesoporous Co3O4 that had been prepared via nanocasting from mesoporous silica... more
ABSTRACT The nanocomposite Co3O4/CoFe2O4 heterostructured mesoporous material was produced via a simple solid–solid reaction of an iron precursor with ordered mesoporous Co3O4 that had been prepared via nanocasting from mesoporous silica as hard template. The magnetic behavior of the exchange-coupled antiferromagnetic/ferrimagnetic (AFM/FM) system was investigated via superconducting quantum interference device (SQUID) magnetometry and 57Fe Mössbauer spectroscopy. The low-temperature magnetization loops of the Co3O4/CoFe2O4 heterostructure present exchange bias under cooling in an applied magnetic field. The antiferromagnetic ordering temperature of Co3O4 is increased due to the proximity of the hard magnetic CoFe2O4 phase. The nanocomposite Co3O4/CoFe2O4 behaves as an exchange coupled system with a cooperative magnetic switching.
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ABSTRACT Highly ordered mesoporous carbon FDU-16 rhombic dodecahedral single crystals with body-centered cubic structure (space group Im3̅m) have been successfully synthesized by employing an organic−organic assembly of triblock copolymer... more
ABSTRACT Highly ordered mesoporous carbon FDU-16 rhombic dodecahedral single crystals with body-centered cubic structure (space group Im3̅m) have been successfully synthesized by employing an organic−organic assembly of triblock copolymer Pluronic F127 (EO106PO70EO106) and phenol/formaldehyde resol in basic aqueous solution. Synthetic factors (including reaction time, temperature, and stirring rate) are explored for controlling the formation of rhombic dodecahedral single crystals. The optimal stirring rate and the reaction temperature are 300 ± 10 rpm and 66 °C, respectively. High-resolution scanning electron microscopy (HRSEM), scanning transmission electron microscopy (STEM), and ultramicrotomy are applied to study the fine structures of the carbon single crystals. The mesopores are arranged in body-centered cubic symmetry throughout the entire particle. Surface steps are clearly observed in the {110} surface, which suggests a layer-by-layer growth of the mesoporous carbon FDU-16 single crystals. Cryo-SEM results from the reactant solution confirm the formation of resol/F127 unit micelles, further supporting the layer-by-layer growth process. The mesoporous carbon FDU-16 single crystals grow up to the final size of 2−4 μm within 2 days. These findings may have consequences for the growth mechanism of other carbon materials in aqueous solution; moreover, the high-quality single crystals also have potential applications in nanodevice technologies.
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ABSTRACT tHighly ordered mesoporous Cu–Ce–O catalysts with different Cu contents have been synthesized byusing ordered mesoporous silica KIT-6 as a hard template. The mesostructural order of the negativereplica is influenced by the ratio... more
ABSTRACT tHighly ordered mesoporous Cu–Ce–O catalysts with different Cu contents have been synthesized byusing ordered mesoporous silica KIT-6 as a hard template. The mesostructural order of the negativereplica is influenced by the ratio of Cu to Ce. Using XRD, HR-SEM, TEM and EDX analysis, it was found thatthe ordered mesostructures of the nanocomposites degenerate with increasing Cu concentration, dueto CuO leaching during the template removal process and a phase separation at high Cu concentration.Cu ions can replace Ce-ion in the structure of CeO2at Cu concentrations below 40 mol%. However, theCu concentration in the final materials is lower than expected from the ratio used in the synthesis.The activity in preferential oxidation of CO in H2-rich gases (PROX) was tested at a space velocity of60,000 mL h−1gcat−1. The activity of the mesoporous catalysts increases with the concentration of Cuand becomes stable for Cu concentrations higher than 20 mol%. A CO conversion around 100 % can beattained with Cu0.20Ce0.80O2as catalyst at 160◦C. The exit CO concentration can be as low as 70 ppm underthese conditions. The CO2selectivity can reach 100 % at low temperature (60 – 80◦C). Direct loading ofCuO on the surface of mesoporous CeO2leads to large CuO crystals and correspondingly low activity. Theinfluence of the pretreatment atmosphere on activity was also studied. Oxidation–reduction–reoxidationcycling can improve the catalytic activity of the catalysts.