Dissociative adsorption is a process in which a molecule adsorbs onto a surface and simultaneously dissociates into two or more fragments. This process is the basis of many applications, particularly in heterogeneous catalysis reactions. The dissociation involves cleaving of the molecular bonds in the adsorbate, and formation of new bonds with the substrate.
Breaking the atomic bonds of the dissociating molecule requires a large amount of energy, thus dissociative adsorption is an example of chemisorption, where strong adsorbate-substrate bonds are created.[1] These bonds can be atomic, ionic or metallic in nature. In contrast to dissociative adsorption, in molecular adsorption the adsorbate stays intact as it bonds with the surface. Often, a molecular adsorption state can act as a precursor in the adsorption process, after which the molecule can dissociate only after sufficient additional energy is available.[2]
A dissociative adsorption process may be homolytic or heterolytic, depending on how the electrons participating in the molecular bond are divided in the dissociation process. In homolytic dissociative adsorption, electrons are divided evenly between the fragments, while in heterolytic dissociation, both electrons of a bond are transferred to one fragment.[1]
- ^ a b Burwell, Robert L (1976). "Manual of Symbols and Terminology for Physicochemical Quantities and Units - Appendix II. Definitions, Terminology and Symbols in Colloid and Surface Chemistry. Part II: Heterogeneous Catalysis". Pure and Applied Chemistry. 46: 76. doi:10.1351/pac197646010071.
- ^ Oura, Kenjiro; Katayama, Mitsuhiro; Zotov, Andrey V.; Lifshits, Victor G.; Saranin, Alexander A. (2003). Surface Science – An Introduction. Berlin, Heidelberg: Springer. pp. 295–323. ISBN 978-3-662-05179-5.