Bonding chemisorption

Overlap between p orbitals leads to cohesive energies of typically less than 0.4 eV molec The much stronger ionic and covalent bonding have binding energies of 10 and 3 eV atom respectively. Finally, physisorption is the weakest form of absorption to a solid surface characterized by a lack of a true chemical bond (chemisorption) between substrate and adsorbate and will be discussed in Chapter 4 (see e.g., Zangwill, 1988). 

Direct bonds between substrate and adsorbate are loosely divided into weak physical adsorption (physisorption), and stronger chemical bonding (chemisorption). We are here focusing on chemisorption cases, where strong substrate-adsorbate interactions make it reasonable to first consider the direct interactions between the adsorbate and the substrate. In physisorption, this interaction is likely to be competing with the interactions between neighbouring adsorbates which may be of similar strength. 

Step 1. Adsorption of reactant molecules. The reactant molecules A and B strike the catalyst surface. They are held up at the surface by weak vander Waals forces (physical adsorption) or by partial chemical bonds (chemisorption). 

When a species Sz is adsorbed at an electrode surface, it may form a purely physical bond (physisorption) or a much stronger chemical bond (chemisorption). In the latter case the species may transfer a positive or negative charge to the electrode, according to the formal adsorption reaction ... 

The rate of adsorption of a molecular species depends on the nature of the adsorption process. Gas molecules may be held on a surface by the weak van der Waal attractive forces which exist between all molecules or by stronger chemical types of bonds (chemisorption) which depend on the... 

Metallic Strong H bonds 100-350 Primary bond Chemisorption... 

Maxted in his study on the poisoning of metallic catalysts (30) has suggested that this phenomenon occurs because the unshielded structure of the poisoning atom allows strong bonding (chemisorption) between it and the surface of the catalyst. In another publication (31)... 

From magnetic work on nickel powders, Selwood favored a two-bond chemisorption at room temperature. Assuming that the formation of a nickel-carbon bond affects the magnetization of nickel in the same way as a nickel-hydrogen bond, the chemisorption of ethylene on supported nickel at room temperature results in the nickel gaining on the average slightly more than two electrons per molecule. This implies that most of the ethylene is associatively chemisorbed [cf equation (47)], but that a moderate fraction is held... 

Chemisorption involves the formation of a covalent chemical bond. Chemisorption provides the strongest bond, van der Waals forces the weakest [17]. 

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