Atomic and Electronic Structures of Nano-Interface In Au/TiO2 Catalyst - Electron Microscopic Approach -

2002 ◽  
Vol 738 ◽  
Author(s):  
S. Ichikawa ◽  
K. Okazaki ◽  
T. Akita ◽  
M. Okumura ◽  
K. Tanaka ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Catalytic Property ◽  
Size Dependence ◽  
Volume Fraction ◽  
Gold Catalysts ◽  
High Resolution Electron Microscopy ◽  
Electron Microscopic ◽  
Gold Particles ◽  
The Mean ◽  
Bulk Gold

ABSTRACTThe size dependence of the catalytic property of the gold catalysts has been reported. It is especially interesting that the catalytic property of gold suddenly changes to show a platinum-like behavior when the mean size of gold is below 2nm. This phenomenon should be owing to the change of the electronic structure of the gold, however its detail has not been cleared yet. We investigated the size dependence of the mean inner potential of gold catalysts supported on TiO2, which is affected by the outer valence electron, using electron holography and high-resolution electron microscopy. We found the following tendency. When the size of the gold particle is over 5nm, the values of the mean inner potential are the same level as the reported experimental values of the bulk gold (21–23V) and the calculated values of the bulk gold (25–30V). When the size is below 5nm, the mean inner potential begins to increase over 30V, and it begins to increase suddenly over 40V at the size below about 2nm. It indicates that the electronic structure of the gold particles varies from that of the bulk state as the size of the gold particles reduces. Due to the size reduction, the volume fraction of the surface atoms and the interface atoms increases, e.g., almost half of the atoms locate on the surfaces or at the interface in case of the top half of the octahedron particle with the size 1.6nm. The surface dipole and the interface dipole should be formed owing to the electron out of the surface to the vacuum and the local charge transfer from the gold particles to the TiO2 surface. These dipole effects might be effective and one of the reasons for the increase of the mean inner potential of gold particles.

Mean Inner Potential of Nanostructured Noble Metal Catalysts - Pt/TiO2 Catalyst -

2003 ◽  
Vol 788 ◽  
Author(s):  
S. Ichikawa ◽  
T. Akita ◽  
K. Okazaki ◽  
M. Okumura ◽  
K. Tanaka ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Noble Metal ◽  
Gold Particle ◽  
Gold Catalysts ◽  
Metal Catalysts ◽  
Electron Holography ◽  
Gold Particles ◽  
Noble Metal Catalysts ◽  
The Mean ◽  
The Difference

ABSTRACTCatalytic properties of noble metal catalysts are often caused by their nanostructures. Gold catalysts are typical cases. It is especially interesting that the catalytic property of gold suddenly changes to resemble that of platinum when the mean size of gold dispersed on certain oxides is <2nm. This phenomenon should be owing to the change of the local electronic structure of the gold particle or the interface between the gold and the oxides, however its detail has not been cleared yet. We measured the mean inner potential of gold particles supported on TiO2 using electron holography and HREM, and found that the mean inner potential of gold depend largely on the size of the gold particles. When the size is >5nm, the mean inner potential is the same as the reported values of bulk gold (experimental: 21–23V, calculated: 25–30V). When the size is <5nm, it begins to increase >30V, and it begins to increase suddenly >40V at the size <2nm. It indicates that the electronic structure of the gold particle varies from that of the bulk state as the size of the gold reduces due to the nano-size effect or the interaction at the interface, since the mean inner potential is sensitive to the electronic state of the outer valence electron. On the other hand, the behavior of the platinum catalysts is different from that of gold catalysts. When the size of the platinum particle on the TiO2 support is >1.5nm, the mean inner potential of platinum is the same as that of the bulk (∼25V). In case of the particle with the size <1.5nm, it begins to increase and the increase rate is lower than that of the gold particles with the size <2nm. It is suggested to be due to the difference of the interaction with TiO2.

Electron Holographic Nano-Characterization of Gold Catalyst at Interface

2002 ◽  
Vol 727 ◽  
Author(s):  
S. Ichikawa ◽  
T. Akita ◽  
M. Okumura ◽  
M. Haruta ◽  
K. Tanaka
Keyword(s):  
Contact Angle ◽  
Titanium Oxide ◽  
Gold Catalyst ◽  
Three Dimensional ◽  
High Resolution Electron Microscopy ◽  
Electron Holography ◽  
Gold Particles ◽  
Oxide Support ◽  
The Mean ◽  
A Charge

AbstractThe catalytic properties of nanostructured gold catalyst are known to depend on the size of the gold particles and to be activated when the size decreases to a few nanometers. We investigated the size dependence of the three-dimensional nanostructure on the mean inner potential of gold catalysts supported on titanium oxide using electron holography and high-resolution electron microscopy (HREM). The contact angle of the gold particles on the titanium oxide tended to be over 90° for gold particles with a size of over 5 nm, and below 90° for a size of below 2 nm. This decreasing change in the contact angle (morphology) acts to increase the perimeter and hence the area of the interface between the gold and titanium oxide support, which is considered to be an active site for CO oxidation. The mean inner potential of the gold particles also changed as their size decreased. The value of the inner potential of gold, which is approximately 25 V in bulk state, rose to over 40 V when the size of the gold particles was less than 2 nm. This phenomenon indicates the existence of a charge transfer at the interface between gold and titanium oxide. The 3-D structure change and the inner potential change should be attributed to the specific electronic structure at the interface, owing to both the “nano size effect” and the “hetero-interface effect.”

Insight into the Formation of Ultrafine Nanostructures in Bulk Amorphous Zr54.5 Ti7.5Al10Cu20Ni8

2001 ◽  
Vol 703 ◽  
Author(s):  
André Heinemann ◽  
Helmut Hermann ◽  
Albrecht Wiedenmann ◽  
Norbert Mattern ◽  
Uta Kühn ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Volume Fraction ◽  
High Volume ◽  
High Resolution Electron Microscopy ◽  
Scattering Data ◽  
Scanning Calorimetry ◽  
Enhanced Diffusion ◽  
Resolution Electron ◽  
The Mean ◽  
Interparticle Interference

ABSTRACTBulk amorphous Zr54.5 Ti7.5Al10Cu20Ni8 is investigated by means of smal-angle neutron scattering (SANS), differential-scanning calorimetry (DSC), high-resolution electron microscopy (HREM) and other methods. The formation of ultrafine nanostructures in the glassy phase is observed and explained by a new model. Structura fluctuations of randomly distributed partialy ordered domains grow during annealing just below the glass transition temperature by local re-ordering. During anneaing the DSC gives evidence for a increasing volume fraction of the localy ordered domains. At high volume fractions of impinging domains a percolation threshold on the interconnected domain boundaries occurs and enhanced diffusion becomes possible. At that stage SANS measurements lead to satistically significant scattering data. The SANS signals are anayzed in terms of a model taking into account spherica particles surrounded by diffusion zones and interparticle interference effects. The mean radius of the nanocrystaline particles is determined to 1 nm and the mean thickness of the depletion zone is 2 nm. The upper limit for the volume fraction after annealing at 653 K for 4hours is about 20 %. Electron microscopy confirms the size and shows that the particle are crystaline.

How Recyclability can Reduce Induction Period of Gold Nanocatalysts

2019 ◽  
Vol 57 ◽  
pp. 1-6 ◽  
Author(s):  
Sedigheh Ghadamgahi
Keyword(s):  
Catalytic Activity ◽  
Reaction Time ◽  
Gold Particle ◽  
Particle Diameter ◽  
Gold Catalysts ◽  
Gold Particles ◽  
Transmission Electron ◽  
The Mean ◽  
Full Conversion ◽  
Catalytic Test

The effect of recyclability on the catalytic activity of supported Au101(PPh3)21Cl5 nanoparticles (1.0 wt% Au101/AC) was investigated for benzyl alcohol oxidation under mild conditions. The influence of recyclability on the catalytic activity of activated Au101/AC nanocatalysts was studied trough a comparison of gold particle diameter and also catalysts conversion between the fresh (as synthesized) and recycled gold catalysts. The monitoring of gold particle diameters by transmission electron microscopy (TEM) showed that the gold particles size gradually increased during the catalytic reaction. The mean diameter of the fresh gold catalysts increased from approximately 3 to 3.2, 5.1 and 5.3 nm after 1, 2 and 3 h reaction time, respectively. Whereas the average gold particle diameter of the recycled samples were slightly enlarged from approximately 5.3 (the sample recycled after 3 h of the first catalytic test) to 5.7, 5.9 and 6.2 nm with durations of 1, 2 and 3 h reaction time, respectively. Therefore, larger gold particles gradually formed for fresh and also recycled gold catalysts during reaction tests. Meanwhile, the catalytic activity of activated 1.0 wt% Au101/AC catalysts jumped to full conversion when the recycled gold catalysts were utilized due to removing ligand stabilizer from gold particles and so bigger particles had formed.

Changes in the electronic structure of gold particles upon thiol adsorption as a function of the mean particle size

2006 ◽  
Vol 495 (1-2) ◽  
pp. 180-185 ◽  
Author(s):  
Michael Büttner ◽  
Helge Kröger ◽  
Inga Gerhards ◽  
Daniel Mathys ◽  
Peter Oelhafen
Keyword(s):  
Particle Size ◽  
Electronic Structure ◽  
Gold Particles ◽  
Mean Particle Size ◽  
The Mean

Coarsening of Cobalt Precipitates in Copper- Cobalt Alloys

1982 ◽  
Vol 21 ◽  
Author(s):  
T. Eguchi ◽  
Y. Tomokiyo ◽  
K. Oki ◽  
Y. Seno
Keyword(s):  
Aging Time ◽  
Ostwald Ripening ◽  
Volume Fraction ◽  
Early Stage ◽  
Electron Microscopic Observation ◽  
Rate Of Change ◽  
Cube Root ◽  
Electron Microscopic ◽  
The Mean ◽  
Co Alloys

ABSTRACTThe Ostwald ripening of precipitates in Cu-Co alloys was investigated by electron microscopic observation. The variation of the mean particle radius r, and the distribution of relative particle sizes, f(r/r) , were obtained as functions of the aging time at 873K . The shape of f(r/r)was rather sharp and symmetrical around r = T in the early stage. It became broad with the aging and was similar, in the late stage, to the theoretical distribution of Ardell. It appeared that the shape of f(r/r) depends on the volume fraction but the growth rate of F scarcely depends on it. The rate of change of r was proportional to the cube root of the aging time from the early stage of aging.

Electron Holographic Characterization of Nano-Hetero Interface Effect in Gold Catalysts

2004 ◽  
Vol 839 ◽  
Author(s):  
S. Ichikawa ◽  
T. Akita ◽  
K. Okazaki ◽  
K. Tanaka ◽  
M. Kohyama
Keyword(s):  
Gold Particle ◽  
Size Dependence ◽  
Critical Size ◽  
High Resolution Electron Microscopy ◽  
The Other ◽  
Electron Holography ◽  
Bulk State ◽  
Resolution Electron ◽  
The Mean

ABSTRACTWe investigated the atomic structure near the interface and the size dependence of the mean inner potential of gold in Au/TiO2 catalysts prepared by the deposition precipitation (DP) method and the vacuum evaporation (VE) method using high resolution electron microscopy (HREM) and electron holography. The TiO2 supports prepared by DP method and VE method are considered to have oxygen-rich surfaces and titanium-rich surfaces respectively. In case of the Au/TiO2 catalyst prepared by DP method, the mean inner potential of gold increased depending on the size of the particle. When the size of the gold particle is over 5nm, the mean inner potential of gold was the same as that of bulk Au. When the size is below 5nm, the mean inner potential became to increase. It increases suddenly over 40V, particularly in case of below 2nm. It indicates that the electronic state of gold on TiO2 changes from that of bulk state as the size decreases. On the other hand, the mean inner potential of gold in Au/TiO2 catalysts prepared by VE method also increased as the size decreased, but the behavior of the size dependence is different from that of DP method. The critical size of the mean inner potential change is around 3nm. The size of the gold particle was below 3nm, the mean inner potential of gold increased gradually. The mean inner potential of VE method is less than that of DP method with the same particle size in spite of the size below 3nm. The stoichiometry at the interface between Au and TiO2 should be one of the dominant reasons for the behavior difference of the size dependence of the mean inner potential between the preparations.

Ultrafine nanostructure of partially crystallized bulk amorphous Zr54.5Ti7.5Al10Cu20Ni8

2001 ◽  
Vol 34 (5) ◽  
pp. 666-668 ◽  
Author(s):  
Helmut Hermann ◽  
André Heinemann ◽  
Hans-Dietrich Bauer ◽  
Norbert Mattern ◽  
Uta Kühn ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Small Angle Neutron Scattering ◽  
Volume Fraction ◽  
High Resolution Electron Microscopy ◽  
Scattering Data ◽  
Depletion Zone ◽  
Upper Limit ◽  
Resolution Electron ◽  
The Mean ◽  
Interparticle Interference

Bulk amorphous Zr54.5Ti7.5Al10Cu20Ni8was investigated by means of small-angle neutron scattering and high-resolution electron microscopy. Partially crystallized states were generated by annealing. The scattering data were analyzed in terms of a model taking into account both properties of the particles and interparticle interference. The mean radius of the particles is 1.3 nm. They are surrounded by a depletion zone with mean thickness of 2.6 nm. The volume fraction of the particles is estimated from the interparticle interference effect; its upper limit after annealing at 653 K for 4 h is 12%. Electron microscopy confirms the size determined from the scattering data and shows that the particles are crystalline.

Immunocytochemical localization of p65 with one-nanometer gold particles following silver development

1989 ◽  
Vol 47 ◽  
pp. 1042-1043
Author(s):  
Richard W. Burry ◽  
Diane M. Hayes
Keyword(s):  
Plasma Membrane ◽  
Bovine Serum Albumin ◽  
Calf Serum ◽  
Specific Protein ◽  
Immunocytochemical Localization ◽  
Electron Microscopic ◽  
Gold Particles ◽  
Pass Through ◽  
Label Distribution ◽  
Phosphate Buffered Saline

Electron microscopic (EM) immunocytochemistry localization of the neuron specific protein p65 could show which organelles contain this antigen. Antibodies (Ab) labeled with horseradish peroxidase (HRP) followed by chromogen development show a broad diffuse label distribution within cells and restricting identification of organelles. Particulate label (e.g. 10 nm colloidal gold) is highly desirable but not practical because penetration into cells requires destroying the plasma membrane. We report pre-embedding immunocytochemistry with a particulate marker, 1 nm gold, that will pass through membranes treated with saponin, a mild detergent.Cell cultures of the rat cerebellum were fixed in buffered 4% paraformaldehyde and 0.1% glutaraldehyde (Glut.). The buffer for all incubations and rinses was phosphate buffered saline with: 1% calf serum, 0.2% saponin, 0.1% gelatin, 50 mM glycine 1 mg/ml bovine serum albumin, and (not in the HRP labeled cultures) 0.02% sodium azide. The monoclonal #48 to p65 was used with three label systems: HRP, 1 nm avidin gold with IntenSE M development, and 1 nm avidin gold with Danscher development.

“Cavity” formation in superplastically deformed aluminium alloys

1990 ◽  
Vol 48 (4) ◽  
pp. 958-959
Author(s):  
A. Cziráki ◽  
E. Ková-csetényi ◽  
T. Torma ◽  
T. Turmezey
Keyword(s):  
Grain Boundaries ◽  
Aluminium Alloys ◽  
Superplastic Deformation ◽  
Volume Fraction ◽  
Superplastic Forming ◽  
Polished Surface ◽  
Cavity Formation ◽  
Stress Concentrations ◽  
Electron Microscopic ◽  
Commercial Aluminium

It is known that the formation of cavities during superplastic deformation can be correlated with the development of stress concentrations at irregularities along grain boundaries such as particles, ledges and triple points. In commercial aluminium alloys Al-Fe-Si particles or other coarse constituents may play an important role in cavity formation.Cavity formation during superplastic deformation was studied by optical metallography and transmission scanning electron microscopic investigations on Al-Mg-Si and Al-Mg-Mn alloys. The structure of particles was characterized by selected area diffraction and X-ray micro analysis. The volume fraction of “voids” was determined on mechanically polished surface.It was found by electron microscopy that strongly deformed regions are formed during superplastic forming at grain boundaries and around coarse particles.According to electron diffraction measurements these areas consist of small micro crystallized regions. See Fig.l.Comparing the volume fraction and morphology of cavities found by optical microscopy a good correlation was established between that of micro crystalline regions.

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