scholarly journals Model Studies on Heterogeneous Catalysts at the Atomic Scale

2014 ◽  
Vol 57 (10-13) ◽  
pp. 822-832 ◽  
Author(s):  
Hans-Joachim Freund ◽  
Shamil Shaikhutdinov ◽  
Niklas Nilius
Keyword(s):  
Heterogeneous Catalysts ◽  
Atomic Scale ◽  
Model Studies

ChemInform Abstract: Model Studies on Heterogeneous Catalysts at the Atomic Scale: From Supported Metal Particles to Two-dimensional Zeolites

ChemInform ◽  
2014 ◽  
Vol 45 (6) ◽  
pp. no-no
Author(s):  
Hans-Joachim Freund ◽  
Markus Heyde ◽  
Niklas Nilius ◽  
Swetlana Schauermann ◽  
Shamil Shaikhutdinov ◽  
...  
Keyword(s):  
Heterogeneous Catalysts ◽  
Atomic Scale ◽  
Metal Particles ◽  
Abstract Model ◽  
Two Dimensional ◽  
Model Studies ◽  
Supported Metal

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

2013 ◽  
Vol 308 ◽  
pp. 154-167 ◽  
Author(s):  
Hans-Joachim Freund ◽  
Markus Heyde ◽  
Niklas Nilius ◽  
Swetlana Schauermann ◽  
Shamil Shaikhutdinov ◽  
...  
Keyword(s):  
Heterogeneous Catalysts ◽  
Atomic Scale ◽  
Metal Particles ◽  
Two Dimensional ◽  
Model Studies ◽  
Supported Metal

What catalysis needs from the electron microscopist

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.

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.

Atomic Scale Observations of the Chemistry at the Metal–Oxide Interface in Heterogeneous Catalysts

2002 ◽  
Vol 205 (1) ◽  
pp. 1-6 ◽  
Author(s):  
R.F. Klie ◽  
M.M. Disko ◽  
N.D. Browning
Keyword(s):  
Metal Oxide ◽  
Heterogeneous Catalysts ◽  
Atomic Scale ◽  
Oxide Interface

scholarly journals Directing reaction pathways via in situ control of active site geometries in PdAu single-atom alloy catalysts

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Mengyao Ouyang ◽  
Konstantinos G. Papanikolaou ◽  
Alexey Boubnov ◽  
Adam S. Hoffman ◽  
Georgios Giannakakis ◽  
...  
Keyword(s):  
Active Site ◽  
Active Sites ◽  
Heterogeneous Catalysts ◽  
Bimetallic Catalyst ◽  
Theoretical Calculations ◽  
Atomic Scale ◽  
Single Atom ◽  
In Situ Control ◽  
Single Atom Alloy

AbstractThe atomic scale structure of the active sites in heterogeneous catalysts is central to their reactivity and selectivity. Therefore, understanding active site stability and evolution under different reaction conditions is key to the design of efficient and robust catalysts. Herein we describe theoretical calculations which predict that carbon monoxide can be used to stabilize different active site geometries in bimetallic alloys and then demonstrate experimentally that the same PdAu bimetallic catalyst can be transitioned between a single-atom alloy and a Pd cluster phase. Each state of the catalyst exhibits distinct selectivity for the dehydrogenation of ethanol reaction with the single-atom alloy phase exhibiting high selectivity to acetaldehyde and hydrogen versus a range of products from Pd clusters. First-principles based Monte Carlo calculations explain the origin of this active site ensemble size tuning effect, and this work serves as a demonstration of what should be a general phenomenon that enables in situ control over catalyst selectivity.

Atom probe studies of catalyst surfaces: structure and chemistry at atomic level

1995 ◽  
Vol 53 ◽  
pp. 420-421
Author(s):  
G.D.W. Smith ◽  
A. Cerezo ◽  
S. Poulston
Keyword(s):  
Mass Spectrometer ◽  
Heterogeneous Catalysts ◽  
Gas Adsorption ◽  
Atom Probe ◽  
Catalytic Reactions ◽  
Atomic Scale ◽  
Single Atom ◽  
Reaction Products ◽  
Time Resolved ◽  
Metallic Catalyst

The imaged (apex) region of a field ion microscope (FIM) specimen is sharply curved and has a radius of less than lOOnm. It is thus a reasonably good "model" for one half of a single particle of a metallic catalyst. FIM images show good detail of steps, ledges and kink site atoms (Fig. 1). When combined with a time-of-flight mass spectrometer to form an atom probe (AP), single atom chemical identification becomes possible. The FIM-AP combination has considerable value for the study of heterogeneous catalysts and catalytic reactions, but there are problems due to the high field acting on the specimens during observation, and the need to work in a vacuum environment. The most important applications to date have involved studies of the surface of the catalyst material, and of relatively non-labile adsorbates. However, new developments in AP instrumentation have opened the prospect of seeing catalytic reactions occurring on the atomic scale, and analysing the intermediate reaction products in both spatially- and time-resolved modes with high precision. Two main lines of development have contributed to this exciting prospect. Block and co-workers in Berlin produced the Pulsed Field Desorption Mass Spectrometer (PFDMS). In this instrument, a high electric field is initially applied to a FIM specimen in the presence of a reactive gas mixture. The specimen apex is cleaned by raising the field to a level sufficient to produce field evaporation, and then the field is dropped to zero to allow gas adsorption and reaction to occur.

Heterogeneous Catalysts: Atomic Scale

2014 ◽  
pp. 1754-1767
Author(s):  
Robert F. Klie ◽  
Kai Sun ◽  
Mark M. Disko ◽  
Jingyue Liu ◽  
Nigel D. Browning
Keyword(s):  
Heterogeneous Catalysts ◽  
Atomic Scale
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