Model studies on heterogeneous catalysts at the atomic scale: From supported metal particles to two-dimensional zeolites

A detailed understanding of catalytic processes requires structural knowledge of the catalyst system. The surface properties of small metal particles which are highly dispersed on insulating supports must play a dominant role in determining this system's catalytic behavior. Therefore characterization of surface topography and composition of heterogeneous catalysts is important. Surface topography of the carrier materials can be obtained by high resolution secondary electron imaging (SEI) in a STEM. The small metal particles can also be located and their topographic relationship with the support morphology determined. However, an elementally specific signal such as the Auger electrons must be used to extract chemical information about the surface species. High resolution Auger electron spectroscopy (AES) and scanning Auger microscopy (SAM) have recently been incorporated into a UHV STEM. In this paper we report some results from the application of this instrumentation to the study of supported metal clusters.

Download Full-text

Model Studies on Heterogeneous Catalysts at the Atomic Scale

Topics in Catalysis ◽

10.1007/s11244-014-0276-6 ◽

2014 ◽

Vol 57 (10-13) ◽

pp. 822-832 ◽

Cited By ~ 7

Author(s):

Hans-Joachim Freund ◽

Shamil Shaikhutdinov ◽

Niklas Nilius

Keyword(s):

Heterogeneous Catalysts ◽

Atomic Scale ◽

Model Studies

Download Full-text

Characterization of Supported Metal Particles in Heterogeneous Catalysts: Part II. Studies of Low Surface Area, Model Materials

Contribution of Clusters Physics to Materials Science and Technology ◽

10.1007/978-94-009-4374-2_8 ◽

1986 ◽

pp. 255-293

Author(s):

G. B. Raupp ◽

T. J. Udovic ◽

J. A. Dumesic

Keyword(s):

Surface Area ◽

Heterogeneous Catalysts ◽

Metal Particles ◽

Area Model ◽

Supported Metal

Download Full-text

An Ex-SituReactor with Anaerobic Specimen Transfer Capabilities for TEM Studies of Reactive (Catalyst) Specimens

Microscopy and Microanalysis ◽

10.1017/s1431927600009867 ◽

1997 ◽

Vol 3 (S2) ◽

pp. 595-596 ◽

Cited By ~ 4

Author(s):

L. F. Allard ◽

K. S. Ailey ◽

A. K. Datye ◽

W. C. Bigelow

Keyword(s):

Heterogeneous Catalysts ◽

High Energy ◽

Atomic Scale ◽

Metal Particles ◽

High Energy Electron ◽

Particle Structure ◽

Transmission Electron ◽

Alkane Hydrogenolysis ◽

Favorable Conditions ◽

Small Metal Particles

The optimization of currently available catalysts and the development of new ones requires a detailed understanding of the effects of both microstructure and composition on their function. Previous work has demonstrated that information at the atomic-scale on heterogeneous catalysts can be derived using high resolution transmission electron microscopy (TEM). Under favorable conditions, the morphology of heavy metal catalytic particles can be related to catalytic activity. It has been shown that preoxidation can disrupt the surface of small metal particles causing altered activity and selectivity in reactions such as alkane hydrogenolysis. Metals such as Pt, Rh, or Ru are noble and pick up no more than a monolayer of oxygen when exposed to air during sample preparation for microscopy. This oxygen monolayer is not imaged in the microscope, most likely because the oxygen desorbs during exposure to the high energy electron beam. However, when metals such as Fe, Co, Ni, Pd or Cu are exposed to air, there is a corrosive interaction that alters particle structure quite dramatically.

Download Full-text

What catalysis needs from the electron microscopist

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100105539 ◽

1988 ◽

Vol 46 ◽

pp. 694-695

Author(s):

Alexis T. Bell

Keyword(s):

Active Sites ◽

Heterogeneous Catalysts ◽

Catalyst Deactivation ◽

Surface Composition ◽

Internal Surface ◽

Active Phase ◽

Atomic Scale ◽

Metal Catalyst ◽

Internal Surface Area ◽

Porous Support

Heterogeneous catalysts, used in industry for the production of fuels and chemicals, are microporous solids characterized by a high internal surface area. The catalyticly active sites may occur at the surface of the bulk solid or of small crystallites deposited on a porous support. An example of the former case would be a zeolite, and of the latter, a supported metal catalyst. Since the activity and selectivity of a catalyst are known to be a function of surface composition and structure, it is highly desirable to characterize catalyst surfaces with atomic scale resolution. Where the active phase is dispersed on a support, it is also important to know the dispersion of the deposited phase, as well as its structural and compositional uniformity, the latter characteristics being particularly important in the case of multicomponent catalysts. Knowledge of the pore size and shape is also important, since these can influence the transport of reactants and products through a catalyst and the dynamics of catalyst deactivation.

Download Full-text

Electron holography of catalysts

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100138452 ◽

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.

Download Full-text

HREM image simulations for supported metal particle catalysts

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100149519 ◽

1993 ◽

Vol 51 ◽

pp. 736-737 ◽

Cited By ~ 1

Author(s):

Ming-Hui Yao ◽

David J. Smith

Keyword(s):

Fine Particles ◽

Amorphous Material ◽

Chemical Properties ◽

Morphological Features ◽

Metal Particles ◽

Plan View ◽

Profile View ◽

Imaging Conditions ◽

Image Simulations ◽

Supported Metal

The chemical properties of catalysts often depend on the size, shape and structure of the supported metal particles. To characterize these morphological features and relate them to catalysis is one of the main objectives for HREM study of catalysts. However, in plan view imaging, details of the shape and structure of ultra-fine supported particles (<2nm) are often obscured by the overlapping contrast from the support, and supported sub-nanometer particles are sometimes even invisible. Image simulations may help in the interpretation at HREM images of supported particles in particular to extract useful information about the size, shape and structure of the particles. It should also be a useful tool for evaluating the imaging conditions in terms of visibility of supported particles. P. L. Gai et al have studied contrast from metal particles supported on amorphous material using multislice simulations. In order to better understand the influence of a crystalline support on the visibility and apparent morphological features of supported fine particles, we have calculated images of Pt and Re particles supported on TiO2(rutile) in both plan view and profile view.

Download Full-text

Metal nanoparticles supported on two-dimensional graphenes as heterogeneous catalysts

Coordination Chemistry Reviews ◽

10.1016/j.ccr.2015.12.005 ◽

2016 ◽

Vol 312 ◽

pp. 99-148 ◽

Cited By ~ 170

Author(s):

Sergio Navalon ◽

Amarajothi Dhakshinamoorthy ◽

Mercedes Alvaro ◽

Hermenegildo Garcia

Keyword(s):

Metal Nanoparticles ◽

Heterogeneous Catalysts ◽

Two Dimensional

Download Full-text