Electron holography of catalysts

1995 ◽  
Vol 53 ◽  
pp. 416-417
Author(s):  
A. K. Datye ◽  
D. S. Kalakkad ◽  
L. F. Allard ◽  
E. Völkl
Keyword(s):  
Heterogeneous Catalysts ◽  
High Surface ◽  
High Surface Area ◽  
Atomic Scale ◽  
Nano Particles ◽  
Phase Image ◽  
Electron Holography ◽  
Specimen Thickness ◽  
Phase Information ◽  
Particle Structure

The active phase in heterogeneous catalysts consists of nanometer-sized metal or oxide particles dispersed within the tortuous pore structure of a high surface area matrix. Such catalysts are extensively used for controlling emissions from automobile exhausts or in industrial processes such as the refining of crude oil to produce gasoline. The morphology of these nano-particles is of great interest to catalytic chemists since it affects the activity and selectivity for a class of reactions known as structure-sensitive reactions. In this paper, we describe some of the challenges in the study of heterogeneous catalysts, and provide examples of how electron holography can help in extracting details of particle structure and morphology on an atomic scale.Conventional high-resolution TEM imaging methods permit the image intensity to be recorded, but the phase information in the complex image wave is lost. However, it is the phase information which is sensitive at the atomic scale to changes in specimen thickness and composition, and thus analysis of the phase image can yield important information on morphological details at the nanometer level.

Carboxylate-Alumoxanes: Precursors for Heterogeneous Catalysts

1999 ◽  
Vol 581 ◽  
Author(s):  
Christopher D. Jones ◽  
David S. Brown ◽  
Larry L Marshall ◽  
Andrew R. Barrona
Keyword(s):  
Aqueous Solution ◽  
Heterogeneous Catalysts ◽  
Oxide Catalyst ◽  
High Surface ◽  
High Surface Area ◽  
Organic Ligands ◽  
Nano Particles ◽  
Environmentally Benign ◽  
Alumina Support ◽  
Macro Scale

ABSTRACTCarboxylate-alumoxanes are organic substituted alumina nano-particles synthesized from boehmite in aqueous solution which are an inexpensive and environmentally benign precursor for the fabrication of nano-, meso-, and macro-scale aluminum based ceramics. The use of carboxylate-alumoxanes as a novel high surface area alumina support for heterogeneous catalysis will be discussed. The ability to perform further chemistry on the organic ligands of the carboxylate-alumoxanes allows for attachment of catalysts. During calcination, the organic ligands are burned out, leaving behind the catalyst in a well-dispersed manner. To demonstrate this concept, the metathesis of C16 olefins using a molybdenum oxide catalyst supported on alumina will be discussed using the carboxylate-alumoxane method.

Novel Xerogel Catalyst Materials for Hydrogenation Reactions and the Role of Atomic Scale Interfaces

1999 ◽  
Vol 5 (S2) ◽  
pp. 704-705
Author(s):  
P.L. Gai ◽  
K. Kourtakis ◽  
H. Dindi ◽  
S. Ziemecki
Keyword(s):  
High Resolution ◽  
Active Sites ◽  
Heterogeneous Catalysts ◽  
Low Voltage ◽  
High Surface ◽  
Sol Gel ◽  
High Surface Area ◽  
High Resolution Electron Microscopy ◽  
Atomic Scale ◽  
Hydrogenation Reactions

We are developing a new family of heterogeneous catalysts for hydrogenation catalysis. Catalyst synthesis is accomplished using colloidal polymerization chemistry which produce high surface area xerogel catalysts. These xerogels have been synthesized by one-step sol gel chemistry. These catalysts contain ruthenium and modifiers such as gold occluded or incorporated in a titanium oxide matrix. The materials, especially the modified systems exhibit favorable performance in microreactor evaluations for hydrogenation reactions and exhibit high activities. Nanostructural studies have revealed that the materials contain dispersed catalyst clusters which are desirable microstructures for the catalysis since the majority of the atoms are exposed to catalysis and are potentially active sites.The composition and atomic structure of the xerogel catalysts containing ruthenium and other metals have been examined using our in-house developments of environmental high resolution electron microscopy (EHREM) the atomic scale [1-3] and low voltage high resolution SEM (LVSEM)[4] methods.

Off-axis electron holography applied to the study of interfaces

1992 ◽  
Vol 50 (1) ◽  
pp. 244-245
Author(s):  
J.K. Weiss ◽  
M. Gajdardziska-Josifovska ◽  
M. R. McCartney ◽  
David J. Smith
Keyword(s):  
Electric Fields ◽  
Resolution Enhancement ◽  
Interfacial Structure ◽  
Atomic Scale ◽  
Bulk Property ◽  
Electron Holography ◽  
Specimen Thickness ◽  
Composition And Structure ◽  
Chemical Segregation ◽  
Diffraction Effects

Interfacial structure is a controlling parameter in the behavior of many materials. Electron microscopy methods are widely used for characterizing such features as interface abruptness and chemical segregation at interfaces. The problem for high resolution microscopy is to establish optimum imaging conditions for extracting this information. We have found that off-axis electron holography can provide useful information for the study of interfaces that is not easily obtained by other techniques.Electron holography permits the recovery of both the amplitude and the phase of the image wave. Recent studies have applied the information obtained from electron holograms to characterizing magnetic and electric fields in materials and also to atomic-scale resolution enhancement. The phase of an electron wave passing through a specimen is shifted by an amount which is proportional to the product of the specimen thickness and the projected electrostatic potential (ignoring magnetic fields and diffraction effects). If atomic-scale variations are ignored, the potential in the specimen is described by the mean inner potential, a bulk property sensitive to both composition and structure. For the study of interfaces, the specimen thickness is assumed to be approximately constant across the interface, so that the phase of the image wave will give a picture of mean inner potential across the interface.

scholarly journals Characterization of Ag:Zno Thin Films and Their Use in Photoelectrocatalytic Degradation Of Methylene Blue (Mb)

2018 ◽  
Vol 22 (2) ◽  
pp. 109-116
Author(s):  
Bhishma Karki ◽  
Jeevan Jyoti Nakarmi ◽  
Rhiddi Bir Singh ◽  
Manish Banerjee
Keyword(s):  
Noble Metals ◽  
Spray Pyrolysis Technique ◽  
High Surface ◽  
High Surface Area ◽  
Nano Particles ◽  
Mixed Metal Oxide ◽  
Design And Synthesis ◽  
In Situ Deposition ◽  
Photoelectrocatalytic Degradation ◽  
Challenges And Opportunities

The synthesis of functional nano-particles via spray pyrolysis technique (SPT), especially those of catalytic nature, has attracted the interests of scientists and engineers, as well as industries. The rapid and high temperature continuous synthesis yields nano-particles with intrinsic features of active catalysts, that is, high surface area and surface energetic. For these reasons, SPT finds applications in various thermally inducible catalytic reactions. However, the design and synthesis of photocatalysts by SPT requires a knowledge set which is different from that established for thermal catalysts. Unknown to many, this has resulted in frustrations to those entering the field unprepared, especially since SPT appears to be an elegant tool in synthesizing oxide nano-particles of any elemental construct. From simple oxide to doped-oxide, and mixed metal oxide to the in situ deposition of noble metals, this Perspective gives an overview on the development of photocatalysts made by SPT in the last decade that led to a better understanding of the design criteria. Various challenges and opportunities are also highlighted; especially those beyond simple metal oxides, which perhaps contain the greatest potential for the exploitation of photocatalysts design by SPT. Journal of Institute of Science and TechnologyVolume 22, Issue 2, January 2018, Page: 109-116

Metal nanoparticles: ligand free approach towards coupling reactions

2021 ◽  
Vol 01 ◽  
Author(s):  
Sharwari K. Mengane ◽  
Ronghui Wu ◽  
Liyun Ma ◽  
Chhaya S. Panse ◽  
Shailesh N. Vajekar ◽  
...  
Keyword(s):  
Heterogeneous Catalysis ◽  
Metal Nanoparticles ◽  
Surface Area ◽  
Heterogeneous Catalysts ◽  
High Surface ◽  
High Surface Area ◽  
Reaction Medium ◽  
Coupling Reactions ◽  
Research Activities ◽  
Ligand Free

: Catalysis is the multidisciplinary field involving many areas of chemistry, notably in organometallic chemistry and materials science. It has great applications in synthesis of many industrially applicable compounds such as fuels and fine chemicals. The activity and selectivity are a key issue in catalysis that generally allied to high surface area. The current research activities mainly deal with the homogeneous and heterogeneous catalysis. Homogeneous and heterogeneous catalysis have certain drawbacks which restricts their application to great extent but have their own advantages. Hence, it has a predominant concern of current research to find out an alternate to overcome their drawbacks. Therefore, it is highly desirable to find a catalytic protocol that offers high selectivity and excellent product yield with quick and easy recovery. Along with their various applications as alternatives to conventional bulk materials nanomaterial have established its great role in different industrial and scientific applications. Nanocatalysis has emerged as new alternative to the conventional homogeneous and heterogeneous catalysis. The nanomaterials are responsible to enhance surface area of the catalyst, which ultimately increases the catalyst reactants contacts. In addition, it acts as robust material and has high surface area like heterogeneous catalysts. Insolubility of such nanomaterial in reaction medium makes them easily separable, hence, catalyst can be easily separate from the product. Hence, it has been proven that nanocatalysts behave like homogeneous as well as heterogeneous catalysts which work as a bridge between the conventional catalytic systems. Considering these merits; researchers has paid their attention towards applications of nanocatalyst in several organic reactions. This review article focused on the catalytic applications of metal nanoparticles (MNPs) such as Pd, Ag, Au, Cu, Pt in ligand free coupling reactions. In addition, it covers applications of bimetallic and multimetallic nanoparticles in ligand free coupling reactions.

scholarly journals Carbon-Based Catalysts for Biodiesel Production—A Review

2020 ◽  
Vol 10 (3) ◽  
pp. 918 ◽  
Author(s):  
Jack Clohessy ◽  
Witold Kwapinski
Keyword(s):  
Heterogeneous Catalysts ◽  
Catalyst Activity ◽  
High Surface ◽  
High Surface Area ◽  
Acid Catalyst ◽  
Biodiesel Production ◽  
Catalyst Characterization ◽  
Synthesis Methods ◽  
And Performance ◽  
Carbon Based

In recent years, a new class of superior heterogeneous acid catalyst for biodiesel production has emerged. These catalysts offer advantages over their predecessors such as high surface area, elevated acid site density, enhanced catalyst activity, good operation stability and relevant economic affordability in an environmentally friendly frame. This review was concerned with carbon-based solid acid (CBAS) catalysts derived from both carbohydrate and pyrolysis products. A series of CBASs with various origins such as D-glucose, sucrose, starch, cellulose and vegetable oil asphalt, converted to char and sulphonated, have been explored as potential heterogeneous catalysts. Catalyst preparation and synthesis methods were briefly summarized. Catalyst characterization and performance for biofuels related reactions were elucidated, identifying potential research applications. Three catalysts in particular were identified as having potential for industrial application and requiring further research.

scholarly journals Generalized synthesis of high surface area mesoporous metal titanates as efficient heterogeneous catalysts

2020 ◽  
Vol 19 ◽  
pp. 100570
Author(s):  
Wimalika R.K. Thalgaspitiya ◽  
Tharindu Kankanam Kapuge ◽  
Dinithi Rathnayake ◽  
Junkai He ◽  
William S. Willis ◽  
...  
Keyword(s):  
Surface Area ◽  
Heterogeneous Catalysts ◽  
High Surface ◽  
High Surface Area ◽  
Mesoporous Metal

Synthesis of Mesoporous Tungsten Oxide/γ-Alumina and Surfactant-Capped Tungsten Oxide Nanoparticles and Their Catalytic Activities in Oxidative Cleavage of Oleic Acid

2016 ◽  
Vol 14 (4) ◽  
pp. 899-907 ◽  
Author(s):  
Amir Enferadi Kerenkan ◽  
Aimé Serge Ello ◽  
Bousselham Echchahed ◽  
Trong-On Do
Keyword(s):  
Tungsten Oxide ◽  
Heterogeneous Catalysts ◽  
High Surface ◽  
High Surface Area ◽  
Oxidative Cleavage ◽  
Type I ◽  
Type Ii ◽  
Catalytic Activities ◽  
Tungsten Oxide Nanoparticles ◽  
Catalytic Test

Abstract Unsaturated fatty acids can be converted into mono and dicarboxylic acids, which are applicably valuable materials, through oxidative cleavage reaction in the presence of a highly efficient catalyst/oxidant system. In this work, two types of advanced heterogeneous catalysts have been developed; (i) high surface area mesoporous tungsten oxide/γ-alumina mixed metal oxide, and (ii) surfactant-capped tungsten oxide nanoparticles. Various technique including N2 adsorption/desorption isotherms, XRD, SEM, EDS, TGA and catalytic test were used to monitor the physicochemical and catalytic properties of these materials. The characterization results revealed that type (i) materials exhibit high surface area and narrow particle size distribution, and the used surfactant could quantitatively enough cap the surface of type (ii) materials. The catalytic activities of these materials in the oxidative cleavage of oleic acid with H2O2 as oxidant were investigated. GC-MS was used to determine the produced amounts of desired products, azelaic and pelargonic acids. The catalytic test results showed more than 90 % conversion for type (ii) catalyst in 5 h reaction at 120 °C with acceptable production yields for azelaic and pelargonic acids. The significantly higher activity of this catalyst compared to type (i) arises from the interesting surface properties of tungsten oxides nanoparticles, which make them able to exploit the good features of homogeneous and heterogeneous catalysts.

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