Catalysis basic concepts

Wang D, Astruc D. Dendritic catalysis basic concepts and recent trends. Coord Chem Rev 2013 257 2317-34. 

Although the basic concept and the arrangement of the chapters is this second edition are the same as the first, this new edition includes many minor additions and updates related to the advances in processing and catalysis. 

The reader must have already identified some of the basic concepts which play a key role in understanding the electrochemical activation of heterogeneous catalysis catalysis, electrocatalysis, promotion, electrochemical promotion, spillover, backspillover. It is therefore quite important to define these terms unambiguously so that their meaning is clearly determined throughout this book. 

Thus Chapter 2 discusses the phenomenology and basic concepts of classical promotion, a subject quite familiar to catalysis and surface science researchers and graduate students, at a level which should be comfortable to electrochemists, solid state ionics and chemical reaction engineering researchers. 

In principle, sites a, IT, and c need not be association sites as depicted by Ogston but could be steric sites that form obstructions such that the adsorbed molecule is chirally directed. Only one active site is actually required providing the remaining two sites (protuberances or cavities) are different from each other and from the active site that catalyzes the reaction. They could be identical providing they are not symmetrically oriented with respect to the active site (not an isosceles triangle). These are the basic concepts for a chiral environment on a surface and they lead to the three basic methods for creating chiral surfaces in heterogeneous catalysis. 

The development of catalytic asymmetric reactions is one of the major areas of research in the field of organic chemistry. So far, a number of chiral catalysts have been reported, and some of them have exhibited a much higher catalytic efficiency than enzymes, which are natural catalysts.111 Most of the synthetic asymmetric catalysts, however, show limited activity in terms of either enantioselectivity or chemical yields. The major difference between synthetic asymmetric catalysts and enzymes is that the former activate only one side of the substrate in an intermolecular reaction, whereas the latter can not only activate both sides of the substrate but can also control the orientation of the substrate. If this kind of synergistic cooperation can be realized in synthetic asymmetric catalysis, the concept will open up a new field in asymmetric synthesis, and a wide range of applications may well ensure. In this review we would like to discuss two types of asymmetric two-center catalysis promoted by complexes showing Lewis acidity and Bronsted basicity and/or Lewis acidity and Lewis basicity.121... 

Catalysis by sol gel doped silica-based materials has become in the last 20 years a prominent tool to synthesize a vast number of useful molecules both in the laboratory and in industrial plants.12 The underlying basic concept of all sol-gel applications is unique one or more host molecules are entrapped by a sol-gel process within the cages of an amorphous metal oxide where they are accessible to diffusible reactants through the inner pore network, which leads to chemical interactions and reactions (Figure 5.3). 

The basic concept is the intuition that, whether homogeneous or heterogeneous, catalysis is primarily a process controlled by a molecular phenomenon since it implies the catalyzed transformation of molecules into other molecules. It follows that on the surface of metals or metal oxides, sulfides, carbides, nitrides usually involved as heterogeneous catalysts, the relevant surface species and the mechanism of their mutual reactions must be of molecular character, as occurs in homogeneous or enzymatic catalysis. 

Basic Concepts of Homogeneous Catalysis of Electrode Reactions. . 672... 

The last two decades have seen enormous developments in catalyst discovery and optimization tools, notably in the area of high-throughput experimentation (HTE) and process optimization (5). However, the basic concept used for exploring the catalyst space in homogeneous catalysis has not changed Once an active catalyst complex is discovered, small modifications are made on the structure to try and screen the activity of neighboring complexes, covering the space much like an ink drop spreads on a sheet of paper. This is not a bad method, but can we do better with the new tools that are available today ... 

Some of the basic concepts and technologies are described here. Catalysis can be divided into two types (1) homogeneous and (2) heterogeneous reactions. In homogeneous reactions, the reaction occurs between similar species, e.g. liquid-liquid reactions. In heterogeneous reactions, the reaction occurs between different types of species, e.g. gas-solid, liquid-solid and liquid-gas. Many industrial reactions are heterogeneous gas-solid or liquid-solid reactions. We will concentrate first on gas reactions occurring at solid catalyst surfaces ... 

Comparable extension has been given to the research on molecular recognition, catalysis and transport processes (Chapters 2-6) on molecular and supramolecular devices (Chapter 8) and self-processes (Chapter 9). This was done to emphasize the more recently developed topics, despite the much larger volume of work on the former areas that have been described in many instances in the literature. The outline of Chapters 1-7 follows that of earlier reviews. Chapters 8 and 9 bring together approaches from various directions. Chapter 10 places the basic concepts into a broader perspective and is intended to make the score decidedly open ended. 

Reaction via unstable acidic or basic intermediates can be promoted by proton transfer to a base or from an acid, respectively, thus giving rise to base or acid catalysis. The concept is illustrated for nucleophilic attack on carboxamide derivatives (Scheme 11.6). With base catalysis, deprotonation of the first-formed intermediate promotes the forward reaction, as does protonation of the first-formed intermediate with acid catalysis. 

The Development of Basic Concepts of Chemical Kinetics in Heterogeneous Catalysis... 

In this chapter we discuss some of the basic concepts of organometallic chemistry and reaction kinetics that are of special relevance to homogeneous catalysis. The catalytic activity of a metal complex is influenced by the characteristics of the central metal ions and the attached ligands. We first discuss the relevant properties of the metal ion and then the properties of a few typical ligands. 

The stereochemistry of pyridoxal phosphate-catalyzed reactions was last summarized comprehensively in 1971 by Dunathan [2], who outlined many of the basic concepts in this field. Aspects of PLP catalysis have been discussed in other reviews on enzyme reaction stereochemistry (e.g., [9]), and a brief review, emphasizing their own work, has recently been published by the present authors [ 10]. Much work has been done in this field during the past ten years, most of it supporting the concepts laid out in Dunathan s review, often refining the picture and sometimes modifying the original ideas. 

The past several years have witnessed enormons advances in the number and variety of reactions that can be catalyzed with excellent enantioselectivities see Enantioselectivity). The area has recently been comprehensively reviewed with volumes edited by the team of Jacobsen, Pfaltz, and Yamamoto as well as Ojima. These important treatises are quite detailed and cannot be summarized here. The goal of this section is to present some of the most important new approaches to asymmetric catalysis. The basic concepts necessary to understanding catalytic asymmetric reactions have been succinctly described by Bosnich in the first edition of Encyclopedia of Inorganic Chemistry and will not be duplicated here. 

PART I, the molecular design of life, introduces the most important classes of biological macromolecules, including proteins, nucleic acids, carbohydrates, and lipids, and presents the basic concepts of catalysis and enzyme action. Here are two examples of how an evolutionary perspective has shaped the material in these chapters ... 

The essence of these interactions, like that of all interactions in biochemistry, is energy. To understand much of biochemistry—bond formation, molecular structure, enzyme catalysis—we need to understand energy. Thermodynamics provides a valuable tool for approaching this topic. We will revisit this topic in more detail when we consider enzymes (Chapter 8) and the basic concepts of metabolism (Chapter 14). 

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