Chemisorption -catalysis

In heterogeneous catalysis, chemisorption of reagents is a preliminary step of the surface reaction. Thus every discussion about catalytic modification (activity, selectivity, and lifetime of the catalyst), induced by poison deposition, has to be carried out in parallel with a study of the poison... 

Shustorovich, E., Ed. In Metal-Surface Reaction Energetics Theory and Applications to Heterogeneous Catalysis, Chemisorption, and Surface Diffusion Wiley-VCH Weinheim, 1991. 

Dynamic Processes on Solid Surfaces, K. Tamaru. Ed., Plenum (1993). (Book by Japanese authors, dealing with catalysis, chemisorption, surface spectroscopies and surface reactions.)... 

In heterogeneous catalysis chemisorption of the reactants and products on the catalyst surface is of central importance, so that the actual chemical reaction (step 4) can not be considered independently from steps 3 and 5. Therefore, these steps must be included in the microkinetics of the reaction. In cases where the other transport processes discussed above play a role, the term macrokinetics is used. 

Secondary Dechlorination Free chlorine can be destroyed or reduced from OCl to Cl by catalysis, chemisorption on activated carbon, or addition of a chemical reducing agent. While in principle some sort of reduction could be used for the entire process of dechlorination, it would be impractical not to recover most of the chlorine as the element. The reduction or decomposition process therefore is used only as a backup measure. The process is also useful in wastewater treatment. 

Zaera, R, Somoqai, G. A. (1984). Journal of the American Chemical Society, 106,2288. King, D. A. (1984). The chemical physics of solid surfaces and heterogeneous catalysis Chemisorption systems. Part B 3. InD. A. King, D. Woodruff (Eds.), The chemical physics of solid surfaces and heterogeneous catalysis (Vol. 3). Toronto Elsevier Science Ltd. Salmeron, M., Somorjai, G. A. (1982). Journal of Physical Chemistry, 86, 341. 

The solid-gas interface and the important topics of physical adsorption, chemisorption, and catalysis are addressed in Chapters XVI-XVIII. These subjects marry fundamental molecular studies with problems of great practical importance. Again the emphasis is on the basic aspects of the problems and those areas where modeling complements experiment. 

The molecular emphasis of modem chemisorption studies has benefited the field of catalysis by giving depth and scope to the surface chemistry of catalytic processes. To paraphrase King [1], quantitative answers have become possible to the following questions ... 

The plan of this chapter is as follows. We discuss chemisorption as a distinct topic, first from the molecular and then from the phenomenological points of view. Heterogeneous catalysis is then taken up, but now first from the phenomenological (and technologically important) viewpoint and then in terms of current knowledge about surface structures at the molecular level. Section XVIII-9F takes note of the current interest in photodriven surface processes. 

It is now a practice to use a variety of surface characterization techniques in the study of chemisorption and catalysis. The examples given here are illustrative most references in this section as well as throughout the chapter will contain results from several techniques. 

CO oxidation catalysis is understood in depth because potential surface contaminants such as carbon or sulfur are burned off under reaction conditions and because the rate of CO oxidation is almost independent of pressure over a wide range. Thus ultrahigh vacuum surface science experiments could be done in conjunction with measurements of reaction kinetics (71). The results show that at very low surface coverages, both reactants are adsorbed randomly on the surface CO is adsorbed intact and O2 is dissociated and adsorbed atomically. When the coverage by CO is more than 1/3 of a monolayer, chemisorption of oxygen is blocked. When CO is adsorbed at somewhat less than a monolayer, oxygen is adsorbed, and the two are present in separate domains. The reaction that forms CO2 on the surface then takes place at the domain boundaries. 

Adapted from Marcinkowsky Berty, J. Catalysis, 29, 3, 1973 Academic Press. Figure 7.4.2 Ethylene chemisorption on silver. 

However, the experimental evidence collected during recent years, concerning mostly the nickel-copper alloy systems, complicated this almost currently accepted interpretation of the alloy catalytic behavior (45). Chemisorptive and subsequent catalytic phenomena appeared to require a different approach for elucidation. The surface reactivity had to be treated as a localized quality of the atoms at the interface, influenced by their neighbors in the crystal lattice (78-80). A detailed general discussion of catalysis on alloys is beyond the scope of this review. In the monograph by Anderson (81) and in the review by Moss and Whalley (82), recently published, a broad survey of the catalytic reactivity of alloys may be found. 

Some General Aspects of Chemisorption and Catalysis Takao Kwan... 

M. McD. Baker and G. I. Jenkins Chemisorption and Catalysis on Oxide Semiconductors... 

Field Emission Microscopy and Some Applications to Catalysis and Chemisorption Robert Gomer... 

Chemisorption and Catalysis on Metallic Oxides F. S. Stone Radiation Catalysis... 

More recently, Silva et a/.447,448 have found that the temperature coefficients of dEa /dT for a number of stepped Au surfaces do not fit into the above correlation, being much smaller than expected. These authors have used this observation to support their view of the hydrophilicity sequence the low 9 (rs0/97 on stepped surfaces occurs because steps randomize the orientation of water dipoles. Besides being against common concepts of reactivity in surface science and catalysis, this interpretation implies that stepped surfaces are less hydrophilic than flat surfaces. According to the plot in Fig. 25, an opposite explanation can be offered the small BEod0/dT of stepped surfaces is due to the strong chemisorption energy of water molecules on these surfaces. 

There is a very rich literature and a comprehensive book6 on the role of promoters in heterogeneous catalysis. The vast majority of studies refers to the adsorption of promoters and to the effect of promoters on the chemisorptive state of coadsorbed species on well characterized single crystal surfaces. A... 

Catalysis and also promotion are intimately related to the phenomenon of chemisorption. For a catalytic reaction ... 

An indication of growing interdisciplinary interest in the field is illustrated in a review on new perspectives in surface chemistry and catalysis by Roberts (.160), who discussed the interaction of N2 with iron surfaces. In so doing, he referred to the Fe (N2) , matrix Mdssbauer work of Barrett and Montano (7), which showed that molecular nitrogen only bonds to iron when the latter is present as a dimer. As the chemisorption studies (161) indicated that N2 is absorbed on singleatom sites, Roberts suggested (160), of the matrix data (7), "if this is correct, then our assignment of the N(ls) peak at 405 eV to end-on chemisorbed N2 will require further investigation. Other reviews that consider matrix-isolation techniques for chemisorption simulation are collected in footnote a. 

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