Steps in heterogeneous catalysis

ErtI G 1990 Elementary steps in heterogeneous catalysis Agnew. Chem., Int. Ed. Engl. 29 1219... 

G. Ertl, Elementary steps in heterogeneous catalysis, Angew. Chem. Int. Ed., 1990, 29, 1219. 

Surface Organometallic Chemistry for Study of the Elementary Steps in Heterogeneous Catalysis... 

Y. Iwasawa, Elementary Reaction Steps in Heterogeneous Catalysis (R. W. Joyner and R. A. van Santen Eds.), NATO ASI Series, Kluwer, the Netherlands, 1993 pp. 287-304. ... 

As discussed earlier, the first step in heterogeneous catalysis is the adsorption of the molecules of the reactants on the surface of the adsorbent or of the catalyst (inner and outer surfaces). Then, molecular dissociation of at least one or two reacting components takes place, usually preceded by surface diffusion. The next step is a surface reaction, which is... 

In an area of considerably less understanding, photosubstitution chemistry may play a key role in elucidating certain steps in heterogeneous catalysis. There now exist a number of reports where photodesorption and photoadsorption to catalytic surfaces occurs. 0 91 These may be viewed as complicated photosubstitution reactions and there are some reports that these reactions can measurably influence the rate of the catalytic transformation of substrates.90,91 ... 

The special economic role of metal and oxide surfaces in heterogeneous catalysis has provided a lot of the driving force behind current surface chemistry and physics. We always knew that the chemistry took place at the surface. But it is only today that we are discovering the basic mechanistic steps in heterogeneous catalysis. It s an exciting time how wonderful to learn precisely how Dobereiner s lamp and the Haber process work ... 

The concept of rate control by a single step, with all other steps at quasiequilibrium, is the norm in heterogeneous catalysis, as it is in almost all of the work on multistep homogeneous kinetics to date. Possible rate-controlling steps in heterogeneous catalysis include the attachment of a reactant to, or detachment of a product from, the catalyst surface rather than only chemical conversions. 

Laser supported high temperature MAS NMR. A new method for time resolved in situ studies of reaction steps in heterogeneous catalysis... 

Surface Science as a Basis for Understanding Heterogeneous Catalysis. In R.W. Joyner and R.A. van Santen, editors. Elementary Reaction Steps in Heterogeneous Catalysis. Kluwer Academic Publishers, Dordrecht, The Netherlands, in press, (1993). 

In this section the use of oxide surfaces as templates will be discussed. These surfaces are particularly interesting because of their potential use in industrial applications in which insulating or inert substrates are required. In this context one has to refer to nanocatalysts or electronic devices, which nowadays rely on an active patterning of the surface. Oxidic templates can be used for the fabrication of well-ordered model systems in these fields, fii fact the search for more powerful catalysts is often hampered by the fact that the complexity of the real world catalyst does not allow an in-depth investigation. Ordered nanostructured model catalysts prepared in a template-controlled process can provide a pathway to systems of lower complexity, which opens a route to the investigation of basic steps in heterogeneous catalysis. 

The initial step in heterogeneous catalysis is usually adsorption of reactants. Adsorption refers to the binding of molecules to a surface, whereas absorption refers to the uptake of molecules into the interior of a substance. — (Section 13.6) Adsorption occurs because the atoms or ions at the surface of a solid are extremely reactive. Unlike their counterparts in the interior of the substance, surface atoms and ions have unused bonding capacity that can be used to bond molecules from the gas or solution phase to the surface of the solid. 

Scheme 3.2 Pictorial illustration of the elementary steps in heterogeneous catalysis (i) adsorption, (ii) reaction, and (iii) desorption.

Bennett, C.O., 1967. A dynamic method for the study of heterogeneous catalytic kinetics. AICHE J. 13, 890-895. Bennett, C.O., 1976. The transient method and elementary steps in heterogeneous catalysis. Catal. Rev. 13,121-148. Bennett, C.O., 2000. Experiments and processes in the transient regime for heterogeneous catalysis. In Haag, W.O., Gates, B., Knozinger, H. (Eds.), Advances in Catalysis. Elsevier Sciences, Dordrecht, pp. 329-416. 

The first step in heterogeneous catalysis involves the diffusion of the reacting gas molecules onto the surface of the catalyst. The second step involves the adsorption (Figure 16.29) of the reacting gas molecules onto the surface of the metal, where they are temporarily bonded to the surface by weak intermolecular forces and/or dative or coordinate covalent bonds. 

Bennett, C.O. (1976) The transient method and elementary steps in heterogeneous catalysis. Catal Rev.,... 

The crucial elementary steps in heterogeneous catalysis such as adsorption, dissociation and interaction of reactant molecules, and formation and desorption of products take place at the solid surface of the catalyst. These steps are sensitively influenced hy the composition, the electronic and geometrical structure of the surface, which may differ markedly from the bulk properties. The vital role of such surface processes in heterogeneous oxidation catalysis was one of the driving forces in the development of surface analytical techniques. 

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