Catalysis intermediate compound theory

The Intermediate Compound Theory in Homogeneous and Heterogeneous Catalysis. 51... 

Catalysis, enzyme-substrate and intermediate compound theory in homo-and heterogeneous, V, 51 Catalysts, for acetonation, III, 51 for acetylation of starch, I, 284, 286 Bourguel s, II, 109, 110, 113 for esterification of cellulose, I, 312 in oxidation of carbohydrates by halogens, III, 177... 

The intermediate compound theory of catalysis was extended and clarified by Mercer and Playfair. ... 

The two main theories of catalysis are (i) intermediate compound formation theory and (ii) adsorption theory. 

The reasoning which led the author to make this first shot in the dark regarding the usefulness of combinations of solid compounds as ammonia catalysts was as follows If we assume that a labile iron nitride is an interminate in the catalytic ammonia synthesis, every addition to the iron which favors the formation of the iron nitride ought to be of advantage. In other words, the hypothesis was used that surface catalysis acts via the formation of intermediate compounds between the catalyst and one or more of the reactants. An experimental support for this theory was the fact that a stepwise synthesis via the formation and successive hydrogen reduction of nitrides had been carried out with calcium nitrides (Haber), and cerium nitrides (Lipski). Later, the author found molybdenum nitride as being the best intermediate for such a stepwise synthesis. 

Since Ostwald had no theory of catalysis he proposed superficial analogies a catalyst acts like oil on machinery, or a whip on a tired horse. The formation of intermediate compounds was made probable when J. Wagner showed in the oxidation of ferrous iron by permanganate in presence of chlorides, and J. Brode in the oxidation of hydriodic acid by hydrogen peroxide, that the products depended on the catalyst used. 

Sabatier postulated the formation of different intermediate compounds, each with its own mode of decomposition, and he recognised that some organic reactions are reversible, and where intermediate compounds cannot be isolated, there may be a production of surface compounds (chemisorption), thus linking the two theories of catalysis, the physical and chemical. Recent work has largely confirmed his views. 

Spectrophotometry. The theory of spectra is far advanced. In many cases, compounds can be unambiguously identified by their ultraviolet, visible, or infrared spectra (e.g., see Smith s book [43]). As an example, the double bond of a CO ligand in a complex has a strong characteristic infrared vibration frequency whose exact value depends on the electronic properties of the coordinating metal these, in turn, are affected by the other substituents. In homogeneous catalysis by transition-metal complexes in particular, foremost among them hydrogenation, hydroformylation, and hydrocyanation, spectra have contributed much to the identification of reaction intermediates and thus of pathways. 

Comparing further the multiplet theory with the theory of intermediate surface compounds, we again find also the following difference. According to the multiplet theory, a branching out 39) of a certain intermediate state exists and if the catalytic reaction proceeds much faster after it, it means that there is a presorption catalysis as Roginskii 40) proposed to call this case but if the process evolves much more speedily toward the activated adsorption, one obtains an impression that the latter precedes the catalysis. On the contrary, the theory of intermediate surface compounds implies that it is chemisorption indeed that precedes catalysis (see above). 

Summing up the relations between the multiplet theory and the theory of intermediate surface compounds, one can come to the conclusion that both theories agree in the following They both consider that catalysis is brought about by chemical forces which yield some intermediate species forms. The main difference is that the multiplet theory deals with deformation and structural and energetic factors such as atomic radii and bond energies. Other differences have been pointed out above. Deformation of reacting molecules and bonds is the point that is common to the deformation theories of catalysis of Mendeleev, Zelinskii, and Bodenstein, developed and specified on the basis of modern data. 

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