Catalyses definition

Electrochemical promotion of catalysis definition, 10 limits of, 180, 505 mechanism of, 189, 271 modeling of, 315, 503 origin, 189... 

HIGH-THROUGHPUT EXPERIMENTATION AND COMBINATORIAL CATALYSIS — DEFINITION AND SCOPE... 

Although the definition of catalyst cannot be directly extrapolated for that corresponding to electrocatalyst, the concepts underlying the definition can be effectively used. In a catalyzed reaction, there is a specific interaction between the catalyst and some species involved in the chemical reaction. The specific interaction is then the key point in the catalysis definition and, thus, the electrocatalyst can be defined as an electrode material that interacts specifically with some species involved in the reaction and remains unaltered after the reaction. This definition allows a good distinction between electrocatalyzed and non-electrocatalyzed reactions the existence of specific surface interactions is characteristic of an electrocatalyzed reaction. 

A definition of catalysis similar to that given above was stated first in about 1895 by Wilhelm Ostwald, whose work on catalysis was recognized with a Nobel prize. Sixty years before, Jakob Berzelius had coined the tenn... 

This article is an iatroduction and survey that states the fundamental principles and definitions of catalysis, demonstrates the unity of the subject, and places it ia an appHed perspective. The selection of iadustrial catalytic processes discussed has been made for the sake of ikustrating principles and representative characteristics of catalysis and catalytic processes. Details of the processes are given ia numerous other articles ia the Eniyclopedia. 

A catalyst is a substance that iacreases the rate of approach to equiUbrium of a chemical reaction without being substantially consumed itself. A catalyst changes the rate but not the equiUbrium of the reaction. This definition is almost the same as that given by Ostwald ia 1895. The term catalysis was coiaed ia ca 1835 by Ber2eHus, who recognized that many seemingly disparate phenomena could be described by a single concept. For example, ferments added ia small amounts were known to make possible the conversion of plant materials iato alcohol and there were numerous examples of both decomposition and synthesis reactions that were apparendy caused by addition of various Hquids or by contact with various soHds. 

Definitions of catalysis take several forms, not all of them equivalent. 

The first example of homogeneous transition metal catalysis in an ionic liquid was the platinum-catalyzed hydroformylation of ethene in tetraethylammonium trichlorostannate (mp. 78 °C), described by Parshall in 1972 (Scheme 5.2-1, a)) [1]. In 1987, Knifton reported the ruthenium- and cobalt-catalyzed hydroformylation of internal and terminal alkenes in molten [Bu4P]Br, a salt that falls under the now accepted definition for an ionic liquid (see Scheme 5.2-1, b)) [2]. The first applications of room-temperature ionic liquids in homogeneous transition metal catalysis were described in 1990 by Chauvin et al. and by Wilkes et ak. Wilkes et al. used weekly acidic chloroaluminate melts and studied ethylene polymerization in them with Ziegler-Natta catalysts (Scheme 5.2-1, c)) [3]. Chauvin s group dissolved nickel catalysts in weakly acidic chloroaluminate melts and investigated the resulting ionic catalyst solutions for the dimerization of propene (Scheme 5.2-1, d)) [4]. 

In 1836 Jons Jakob Berzelius considered eight seemingly unrelated experimental results and concluded that there was a common thread among them. The commonality he defined as catalysis. In doing tliis, Berzelius proposed that a catalytic force was responsible for catalytic action. The concept of catalysis is today considered by most researchers to be due to Berzelius, probably because of the popularity of his annual Handbook of Chemistiywhere he published his definition of catalytic action. For the next one hundred years many referred to the phenomenon as contact catalysis or contact action, as proposed by Mitscherlich. 

A recent definition of catalysis that is based on dier-modynamics was advanced by the Subcommittee on Chemical Kinetics, Physical Chemistry Division, lUPA ... 

Another definition of acids and bases is due to G. N. Lewis (1938). From the experimental point of view Lewis regarded all substances which exhibit typical acid-base properties (neutralisation, replacement, effect on indicators, catalysis), irrespective of their chemical nature and mode of action, as acids or bases. He related the properties of acids to the acceptance of electron pairs, and bases as donors of electron pairs, to form covalent bonds regardless of whether protons are involved. On the experimental side Lewis definition brings together a wide range of qualitative phenomena, e.g. solutions of BF3, BC13,... 

Catalysis By definition, a catalyst is a substance (in this book a solid) which can accelerate the approach of a reactive gas mixture to equilibrium, without itself being consumed in this process. 

In this Appendix we summarize some of the most common questions asked by physical chemists when they first encounter NEMCA. There are also questions asked after years of exposure in this area. They have been sampled by the authors from more than 100 presentations in International Conferences on Catalysis, Electrochemistry, Solid State Ionics and Surface Science. Some of the questions are easy to answer, some are difficult and there are even some for which there is still no definitive answer. For the sake of the reader who may want to test his understanding up to this point we are first listing the questions separately, then proceed with their answer. 

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