Metals chemisorption

Figure A.14 Energy diagram for the adsorption of an atom on a d-metal. Chemisorption is described with molecular orbitals constructed from the d-band of the metal and atomic orbitals of the adatom. The chemisorption bond in b) is weaker, because the antibonding chemisorption orbital is partially filled (compare Fig. A.5).

Figure A.15 Energy diagram for the adsorption of a simple diatomic molecule on a d-metal. Chemisorption orbitals are constructed from both the bonding and the antibonding levels of the molecule. As the latter becomes partially occupied, the intramolecular bond of the adsorbate has been activated.

Chemisorption. Chemisorption involves heats of adsorption which are large as compared to the heat of van der Waal s adsorption. The term chemisorption implies formation of semi-chemical bonds of the adsorbed gas with the solid surface. Chemisorption may be a process involving measurable activation energy—that is, a measurable rate of adsorption and a measurable temperature coefficient of rate of adsorption. As in the case of hydrogen adsorption on metals, chemisorption may have no measurable rate of adsorption, the adsorption being essentially instantaneous. 

For catalysts containing reducible oxide supports, as is the case of systems, the chemisorption studies may also be used for detecting the metal deactivation effects due to the occurrence of a SMSI effect (300,301). On MT1O2 catalysts, the classic SMSI systems, it is now well established that reduction at about 773 K strongly inhibits the metal chemisorptive capability (171,302,318-320). The chemisorption data reported for M/Cc(M)02. catalysts have also suggested the occurrence of such an effect. It is certainly an interesting question which deserves some further discussion in this chapter. 

In conclusion, the quantitative analysis of the TPD-H2 results obtained by following the experimental protocol applied in (117) allows to gain very useful information about two major aspects of the hydrogen chemisorption studies, the metal chemisorption capability and the characteristics of the spillover phenomena occurring in these catalysts. 

State of Dispersion of Metal. Chemisorption of carbon monoxide at 23 °C and x-ray diffraction line broadening have been used to measure... 

Prior to the early 1990s, all structural studies of alkali-metal chemisorption found the adatom located at high coordination sites at which the alkali-metal atom is bound in three- or four-fold hollow sites. A comprehensive survey of alkali-metal adsorption studies prior to 1988 may be found in the book edited by Bonzel (Bonzel et al., 1989). Several more recent LEED, SEXAFS and X-ray studies have implicated low coordination (top) sites, as in the case of Cu(lll)p(2x2)-Cs, or substitutional behavior. These results may signal that the current understanding of the alkali-metal bonding at surfaces is incomplete. 

The Effects of Nanostructure on Adsorption Features Metal Chemisorption... 

The Effects of Nanostructure on Adsorption Features Metal Chemisorption on Hexagonal Templated Zirconia Obtained Thorough Sol-Gel Process... 

Figure 3.5. (a) DFT-computed molecular orbitals and energies of molecular CO. Rco = 1-14A bonding = —11.9 eV. (b) Left-handside orbital energy-level diagram for metal chemisorption system of adsorbed CO <75 to be identified with 5cr and (74 to be identified with 4a ttq to be identified with 27t and 7Ti to be identified with Itt. Right-hand side schematic representation of the electronic structure of the transition metal. 

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