scholarly journals Reflections on the value of electron microscopy in the study of heterogeneous catalysts

2017 ◽  
Vol 473 (2197) ◽  
pp. 20160714 ◽  
Author(s):  
John Meurig Thomas
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Active Sites ◽  
Heterogeneous Catalysts ◽  
Three Dimensions ◽  
Single Atom ◽  
Catalyst Characterization ◽  
Solid Catalysts ◽  
Valence States ◽  
Ac Transmission

Electron microscopy (EM) is arguably the single most powerful method of characterizing heterogeneous catalysts. Irrespective of whether they are bulk and multiphasic, or monophasic and monocrystalline, or nanocluster and even single-atom and on a support, their structures in atomic detail can be visualized in two or three dimensions, thanks to high-resolution instruments, with sub-Ångstrom spatial resolutions. Their topography, tomography, phase-purity, composition, as well as the bonding, and valence-states of their constituent atoms and ions and, in favourable circumstances, the short-range and long-range atomic order and dynamics of the catalytically active sites, can all be retrieved by the panoply of variants of modern EM. The latter embrace electron crystallography, rotation and precession electron diffraction, X-ray emission and high-resolution electron energy-loss spectra (EELS). Aberration-corrected (AC) transmission (TEM) and scanning transmission electron microscopy (STEM) have led to a revolution in structure determination. Environmental EM is already playing an increasing role in catalyst characterization, and new advances, involving special cells for the study of solid catalysts in contact with liquid reactants, have recently been deployed.

Biodiesel Production Using Mixed Solid Catalysts

2013 ◽  
Vol 824 ◽  
pp. 451-458
Author(s):  
A.K. Temu
Keyword(s):  
Active Sites ◽  
Heterogeneous Catalysts ◽  
Biodiesel Production ◽  
Environmentally Benign ◽  
Catalyst Loading ◽  
Yield Data ◽  
Continuous Processes ◽  
Solid Catalysts ◽  
Base Catalysts ◽  
Astm D6751

One of the disadvantages of homogeneous base catalysts in biodiesel production is that they cannot be reused or regenerated because they are consumed in the reaction. Besides, homogeneous catalysed process is not environmentally friendly because a lot of waste water is produced in the separation step. Unlike homogeneous, heterogeneous catalysts are environmentally benign, can be reused and regenerated, and could be operated in continuous processes, thus providing a promising option for biodiesel production. This paper presents catalytic activity of single and mixed solid catalysts in production of biodiesel from palm oil using methanol as well as ethanol at atmospheric pressure. The catalysts used are CaO, K2CO3, Al2O3, and CaO/K2CO3, CaO/Al2O3, K2CO3/Al2O3 mixtures. Results show that methanol is a better reactant with biodiesel yield ranging from 48 to 96.5% while ethanol gives yields ranging from 20 to 95.2%. The yield data for single catalysts range from 20 to 89.2% while that for mixed catalysts range from 52 to 96.5% indicating improvement in the activity by mixing the catalysts. The study also shows that biodiesel yield increases with catalyst loading which emphasizes the need for sufficient number of active sites. The properties of biodiesel produced compares well with ASTM D6751 and EN 14124 biodiesel standards.

scholarly journals Quantitative High-Resolution Transmission Electron Microscopy of Single Atoms

2011 ◽  
Vol 18 (1) ◽  
pp. 212-217 ◽  
Author(s):  
Björn Gamm ◽  
Holger Blank ◽  
Radian Popescu ◽  
Reinhard Schneider ◽  
André Beyer ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
High Resolution ◽  
Form Factors ◽  
Absolute Intensity ◽  
Quantitative Agreement ◽  
Single Atom ◽  
Simulated Image ◽  
Single Atoms ◽  
Transmission Electron

AbstractSingle atoms can be considered as the most basic objects for electron microscopy to test the microscope performance and basic concepts for modeling image contrast. In this work high-resolution transmission electron microscopy was applied to image single platinum, molybdenum, and titanium atoms in an aberration-corrected transmission electron microscope. The atoms are deposited on a self-assembled monolayer substrate that induces only negligible contrast. Single-atom contrast simulations were performed on the basis of Weickenmeier-Kohl and Doyle-Turner form factors. Experimental and simulated image intensities are in quantitative agreement on an absolute intensity scale, which is provided by the vacuum image intensity. This demonstrates that direct testing of basic properties such as form factors becomes feasible.

Advanced Electron Microscopy Characterization of Nanostructured Heterogeneous Catalysts

2004 ◽  
Vol 10 (1) ◽  
pp. 55-76 ◽  
Author(s):  
Jingyue Liu
Keyword(s):  
Electron Microscopy ◽  
Heterogeneous Catalysis ◽  
Heterogeneous Catalysts ◽  
Nanostructured Catalysts ◽  
Catalyst Characterization ◽  
Challenges And Opportunities ◽  
Recent Developments ◽  
Microscopy Characterization ◽  
Microscopy Techniques

Heterogeneous catalysis is one of the oldest nanosciences. Although model catalysts can be designed, synthesized, and, to a certain degree, characterized, industrial heterogeneous catalysts are often chemically and physically complex systems that have been developed through many years of catalytic art, technology, and science. The preparation of commercial catalysts is generally not well controlled and is often based on accumulated experiences. Catalyst characterization is thus critical to developing new catalysts with better activity, selectivity, and/or stability. Advanced electron microscopy, among many characterization techniques, can provide useful information for the fundamental understanding of heterogeneous catalysis and for guiding the development of industrial catalysts. In this article, we discuss the recent developments in applying advanced electron microscopy techniques to characterizing model and industrial heterogeneous catalysts. The importance of understanding the catalyst nanostructure and the challenges and opportunities of advanced electron microscopy in developing nanostructured catalysts are also discussed.

scholarly journals Metal-Organic Frameworks as Versatile Heterogeneous Solid Catalysts for Henry Reactions

Molecules ◽  
2021 ◽  
Vol 26 (5) ◽  
pp. 1445
Author(s):  
Francisco G. Cirujano ◽  
Rafael Luque ◽  
Amarajothi Dhakshinamoorthy
Keyword(s):  
Active Sites ◽  
Heterogeneous Catalysts ◽  
Final Section ◽  
Metal Organic Frameworks ◽  
Henry Reaction ◽  
Solid Catalysts ◽  
Wide Range ◽  
Metal Organic ◽  
Materials Used ◽  
Heterogeneous Solid

Metal–organic frameworks (MOFs) have become one of the versatile solid materials used for a wide range of applications, such as gas storage, gas separation, proton conductivity, sensors and catalysis. Among these fields, one of the more well-studied areas is the use of MOFs as heterogeneous catalysts for a broad range of organic reactions. In the present review, the employment of MOFs as solid catalysts for the Henry reaction is discussed, and the available literature data from the last decade are grouped. The review is organized with a brief introduction of the importance of Henry reactions and structural properties of MOFs that are suitable for catalysis. The second part of the review discusses the use of MOFs as solid catalysts for the Henry reaction involving metal nodes as active sites, while the third section provides data utilizing basic sites (primary amine, secondary amine, amides and urea-donating sites). While commenting on the catalytic results in these two sections, the advantage of MOFs over other solid catalysts is compared in terms of activity by providing turnover number (TON) values and the structural stability of MOFs during the course of the reaction. The final section provides our views on further directions in this field.

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