Studies of Supported Metal Catalysts Using Low Voltage Biased Secondary Electron Imaging in a JSM-6320f Fe-SEM

1997 ◽  
Vol 3 (S2) ◽  
pp. 1223-1224
Author(s):  
J. Liu ◽  
R. L. Ornberg ◽  
J. R. Ebner
Keyword(s):  
Secondary Electron ◽  
Low Voltage ◽  
Supported Catalysts ◽  
High Surface ◽  
High Surface Area ◽  
Incident Beam ◽  
Active Species ◽  
Supported Metal Catalysts ◽  
Active Components ◽  
Electron Imaging

Many industrial catalysts have a complex geometric structure to enable reacting gases or fluids to reach as much of the active surface of the catalyst as possible. The catalyzing surface frequently consists of a complex chemical mixture of different phases produced by an evolved chemical process. The active components are often very small particles dispersed on high-surface-area supports. The catalytic properties of this type of catalyst depend on the structure, composition, and morphology of the active species as well as the supports. TEM/STEM and associated techniques have been used extensively to characterize the structure and composition of supported catalysts. Surface morphology of supported catalysts is generally examined by secondary electron imaging, especially at low incident beam energies. It is, however, frequently found that small metal particles are not usually seen in SE images because of the complication of support topography

Studies of supported catalysts by high-resolution SEM in an UHV STEM

1991 ◽  
Vol 49 ◽  
pp. 502-503
Author(s):  
J. Liu ◽  
G. E. Spinnler
Keyword(s):  
High Resolution ◽  
Supported Catalysts ◽  
High Surface ◽  
High Surface Area ◽  
Incident Beam ◽  
Supported Metal Catalysts ◽  
Support Materials ◽  
Exit Surface ◽  
Scanning Transmission

In the studies of the materials used in practical heterogeneous catalysis scanning transmission electron microscopy (STEM) is particularly suited for the characterization of particle size, shape, structure and composition of inhomogeneous catalyst systems by the combined use of a variety of techniques. Recently a high resolution surface imaging technique has been realized in STEM by collecting secondary electrons (SE) emitted at the exit surface of the sample. The application of this imaging mode to the study of supported metal catalysts has proven very useful in the characterization of the support topography with subnanometer resolution. However these studies are confined to extremely thin areas due to the fact that the incident beam will be scattered before encountering the exit surfaces of the sample. This will affect the resolution of SE images, especially for the study of high surface area support materials such as γ-Al2O3 carriers. Furthermore it has been frequently found diat metal particles are not usually seen in the SE images even when the particles are situated on the exit surfaces of the supporting materials.1 As part of an on-going project for characterizing supported catalysts we report here some preliminary results on high resolution SE imaging of supported catalysts in a UHV STEM.

High-Resolution Scanning Electron Microscopy and Microanalysis of Supported Metal Catalysts

1999 ◽  
Vol 589 ◽  
Author(s):  
Jingyue Liu
Keyword(s):  
High Resolution ◽  
Low Voltage ◽  
Supported Catalysts ◽  
Metal Catalysts ◽  
Supported Metal Catalysts ◽  
Surface Sensitivity ◽  
Brightness Field ◽  
Backscattered Electron ◽  
Enhanced Surface ◽  
Supported Metal

AbstractThe use of a high-brightness field emission gun and novel secondary electron detection systems makes it possible to acquire nanometer-resolution surface images of bulk materials, even at low electron beam voltages. The advantages of low-voltage SEM include enhanced surface sensitivity, reduced sample charging on non-conducting materials, and significantly reduced electron range and interaction volume. High-resolution images formed by collecting the backscattered electron signal can give information about the size and spatial distribution of metal nanoparticles in supported catalysts. Low-voltage XEDS can provide compositional information of bulk samples with enhanced surface sensitivity and significantly improved spatial resolution. High-resolution SEM techniques enhance our ability to detect and, subsequently, analyze the composition of nanoparticles in supported metal catalysts. Applications of high-resolution SEM imaging and microanalysis techniques to the study of industrial supported catalysts are discussed.

C-H bond functionalization using Pd and Au supported catalysts with mechanistic insights of the active species

Synthesis ◽  
2021 ◽  
Author(s):  
Tamao Ishida ◽  
Zhenzhong Zhang ◽  
Haruno Murayama ◽  
Eiji Yamamoto ◽  
Makoto Tokunaga
Keyword(s):  
Aromatic Compounds ◽  
Reaction Mechanisms ◽  
Bond Activation ◽  
Supported Catalysts ◽  
Metal Catalysts ◽  
Active Species ◽  
Supported Metal Catalysts ◽  
Bond Functionalization ◽  
Bond Forming ◽  
Supported Metal

The C–H functionalization has been extensively studied as a direct C–C bond forming reaction with high atomic efficiency. The efforts have also been made on the reaction using supported catalysts, which are superior in terms of catalyst separation from the reaction mixture and reusability. In this review, an overview of the C–H functionalization reactions, especially for Pd and Au supported catalysts will be described. In particular, we discuss reaction mechanisms, active species, leaching, reusability, etc. 1 Introduction 2 Types of supported metal catalysts and their active species 3 Modes of C–H bond activation 4 Oxidative C–H C–H coupling of aryl compounds 5 C–H C–H coupling where one side is aromatic 6 C–H acylation of aromatic compounds and related reactions 7 Conclusion

Visibility of Small Metalllic Catalyst Particles in High-Resolution Secondary and Backscattered Electron Images

1999 ◽  
Vol 5 (S2) ◽  
pp. 720-721
Author(s):  
Jingyue Liu
Keyword(s):  
High Resolution ◽  
Metallic Nanoparticles ◽  
Low Voltage ◽  
High Surface ◽  
High Surface Area ◽  
Metal Catalyst ◽  
Catalyst Supports ◽  
Metallic Particles ◽  
Backscattered Electrons ◽  
Backscattered Electron

Metallic nanoparticles finely dispersed onto high surface-area supports play an important role in heterogeneous catalysis. The performance of a supported metal catalyst can be directly related to the size and spatial distribution of the metallic nanoparticles. With the recent development of highresolution SEM instruments, it is now possible to observe nanoparticles in a field emission SEM. At low voltages, surface details of catalyst supports as well as metallic nanoparticles can be observed. The particle contrast in low voltage SEM images, however, is still not well understood. We have previously shown that the contrast of metallic particles can be enhanced if a small positive potential is applied to the sample. It is suggested that backscattered electrons (BE) significantly contribute to the visibility of metallic nanoparticles in high-resolution SE images. In this paper, we report further study on the origin of particle contrast in high-resolution SE images.Figure 1 shows a set of SE images of the same area of a carbon supported Pt catalyst.

scholarly journals Modern Trends in Design of Catalysts for Transformation of Biofuels into Syngas and Hydrogen: From Fundamental Bases to Performance in Real Feeds

Energies ◽  
2021 ◽  
Vol 14 (19) ◽  
pp. 6334
Author(s):  
Vladislav Sadykov ◽  
Mikhail Simonov ◽  
Nikita Eremeev ◽  
Natalia Mezentseva
Keyword(s):  
Natural Gas ◽  
High Surface ◽  
High Surface Area ◽  
Internal Heat ◽  
Pilot Scale ◽  
Platinum Group Metals ◽  
Atomic Scale ◽  
Active Components ◽  
Structured Catalysts ◽  
Metal Support Interaction

This review considers problems related to design of efficient structured catalysts for natural gas and biofuels transformation into syngas. Their active components are comprised of fluorite, perovskite and spinel oxides or their nanocomposites (both bulk and supported on high surface area Mg-doped alumina or MgAl2O4) promoted by platinum group metals, nickel and their alloys. A complex of modern structural, spectroscopic and kinetic methods was applied to elucidate atomic-scale factors controlling their performance and stability to coking, such as dispersion of metals/alloys, strong metal-support interaction and oxygen mobility/reactivity as dependent upon their composition and synthesis procedures. Monolithic catalysts comprised of optimized active components loaded on structured substrates with a high thermal conductivity demonstrated high activity and stability to coking in processes of natural gas and biofuels reforming into syngas. A pilot-scale axial reactor equipped with the internal heat exchanger and such catalysts allowed to efficiently convert into syngas the mixture of natural gas, air and liquid biofuels in the autothermal reforming mode at low (~50–100 °C) inlet temperatures and GHSV up to 40,000 h−1.

Low voltage electrolyte-gated organic transistors making use of high surface area activated carbon gate electrodes

2014 ◽  
Vol 2 (28) ◽  
pp. 5690-5694 ◽  
Author(s):  
J. Sayago ◽  
F. Soavi ◽  
Y. Sivalingam ◽  
F. Cicoira ◽  
C. Santato
Keyword(s):  
Activated Carbon ◽  
Surface Area ◽  
Low Voltage ◽  
Low Cost ◽  
High Surface ◽  
High Surface Area ◽  
Reference Electrode ◽  
Organic Transistors ◽  
Gate Electrodes ◽  
External Reference

The use of high surface area, low cost, activated carbon gate electrodes enables low voltage (sub-1 V) operation in ionic liquid-gated organic transistors and renders unnecessary the presence of an external reference electrode to monitor the channel potential.

Image Formation With Upper and Lower Secondary Electron Detectors in the Low Voltage Field-Emission SEM

1998 ◽  
Vol 4 (S2) ◽  
pp. 260-261
Author(s):  
J. Liu
Keyword(s):  
High Resolution ◽  
Field Emission ◽  
Secondary Electron ◽  
Low Voltage ◽  
Incident Beam ◽  
Sample Surface ◽  
Backscattered Electrons ◽  
Sample Chamber ◽  
Scale Surface ◽  
Short Working

High-resolution secondary electron (SE) imaging was first demonstrated at 100 kV in the STEM a decade ago. High-resolution SE imaging is now routinely obtainable in field-emission SEMs. Although nanometer-scale surface features can be examined at low incident beam voltages we still do not fully understand the factors that affect the contrast of low voltage SE images. At high incident beam voltages, SE1 (SEs generated by the incident probe) and SE2 (SEs generated by backscattered electrons at the sample surface) can be spatially separated. SE1 carries high-resolution detail while SE2 contributes to background. At low incident beam voltages, however, the interaction volume of the incident electrons shrinks rapidly with decreasing incident beam voltage. Thus, both the SE1 and SE2 signals carry high-resolution information. At low incident beam voltages, SE3 (SEs generated by backscattered electrons impinging on the sample chamber, pole pieces and etc.) also carries high-resolution detail and contributes significantly to the collected signal, especially for high atomic number materials and at short working distances.

scholarly journals Ruthenium particle size and cesium promotion effects in Fischer–Tropsch synthesis over high-surface-area graphite supported catalysts

2017 ◽  
Vol 7 (5) ◽  
pp. 1235-1244 ◽  
Author(s):  
José L. Eslava ◽  
Xiaohui Sun ◽  
Jorge Gascon ◽  
Freek Kapteijn ◽  
Inmaculada Rodríguez-Ramos
Keyword(s):  
Particle Size ◽  
Surface Area ◽  
Supported Catalysts ◽  
High Surface ◽  
High Surface Area ◽  
Tropsch Synthesis ◽  
Fischer Tropsch ◽  
Fischer Tropsch Synthesis

The effect of ruthenium particle size on Fischer–Tropsch synthesis has been studied at 513 K, H2/CO = 2 and 15 bar.

Low-Voltage scanning electron microscope (LVSEM) determination of nevirapine Crystal Habit in a Pharmaceutical Suspension

1992 ◽  
Vol 50 (2) ◽  
pp. 1326-1327
Author(s):  
A. Angel ◽  
R. Peischl ◽  
A. Hawi
Keyword(s):  
Low Voltage ◽  
Aqueous Suspension ◽  
High Surface ◽  
High Surface Area ◽  
Crystal Form ◽  
Transcriptase Inhibitor ◽  
Crystal Habit ◽  
Stable Form ◽  
Subsequent Conversion ◽  
Reverse Transcriptase Inhibitor

LVSEM permits the examination of materials with reduced radiation damage and high contrast, factors which are critical to the successful examination of organic crystals. In this study, LVSEM was applied to characterize the structure of a beam sensitive anhydrous crystal form and its subsequent conversion to the hemihydrate form in an aqueous suspension.Nevirapine, a dipyridodiazepenone compound, is a reverse transcriptase inhibitor currently being developed for the treatment of AIDS. Nevirapine exists as the hemihydrate stable form and as the anhydrous metastable form. The hemihydrate crystals are multifaceted blades (Fig. 1) whereas the anhydrous form exists predominately as large agglomerates of porous “coral like” crystals with high surface area (Fig. 2). When formulated in aqueous suspensions, anhydrous Nevirapine converted into the hemihydrate form, with eventual growth of the hemihydrate crystals. The extent of conversion and rate of growth have been determined to be a function of temperature and time. LVSEM was used to study the anhydrous-to-hemihydrate conversion as the two forms could easily be identified by their characteristic morphology.

scholarly journals Titanium Dioxide as a Catalyst Support in Heterogeneous Catalysis

2014 ◽  
Vol 2014 ◽  
pp. 1-21 ◽  
Author(s):  
Samira Bagheri ◽  
Nurhidayatullaili Muhd Julkapli ◽  
Sharifah Bee Abd Hamid
Keyword(s):  
Active Sites ◽  
Heterogeneous Catalysts ◽  
High Surface ◽  
Catalyst Support ◽  
High Surface Area ◽  
Supported Metal Catalysts ◽  
Support Material ◽  
Oxidation Reactions ◽  
Base Property ◽  
Metal Support Interaction

The lack of stability is a challenge for most heterogeneous catalysts. During operations, the agglomeration of particles may block the active sites of the catalyst, which is believed to contribute to its instability. Recently, titanium oxide (TiO2) was introduced as an alternative support material for heterogeneous catalyst due to the effect of its high surface area stabilizing the catalysts in its mesoporous structure. TiO2supported metal catalysts have attracted interest due to TiO2nanoparticles high activity for various reduction and oxidation reactions at low pressures and temperatures. Furthermore, TiO2was found to be a good metal oxide catalyst support due to the strong metal support interaction, chemical stability, and acid-base property. The aforementioned properties make heterogeneous TiO2supported catalysts show a high potential in photocatalyst-related applications, electrodes for wet solar cells, synthesis of fine chemicals, and others. This review focuses on TiO2as a support material for heterogeneous catalysts and its potential applications.

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