1. Electronic structure and ensemble size effects in hydrocarbon reactions on alloys
- Author
-
H. C. De Jongste and V. Ponec
- Subjects
chemistry.chemical_classification ,Chemistry ,Bond strength ,Alloy ,Inorganic chemistry ,General Chemistry ,Electronic structure ,engineering.material ,Catalysis ,Condensed Matter::Materials Science ,Hydrocarbon ,Adsorption ,Chemical physics ,Chemisorption ,engineering ,Reactivity (chemistry) - Abstract
In this paper, introductory to the Symposium, an attempt is made to summarize and rationalize the available information on the reforming reactions of hydrocarbons on metals and alloys. It is shown that three important aspects of hydrocarbon adsorption, viz. chemisorption bond strength, reactivity towards C-H bonds and the ability to form multiple bonds with the group VIII metals, are not dramatically changed by alloying. Therefore, various changes due to alloying observed in the selectivity of alloys are ascribed to the availability of ensembles of active sites on the alloy surface (ensemble size effects). It is shown that also on pure metals various intermediates are identified which differ in the number of C- atoms and metal-atoms involved in the formation of activated complexes. By alloying a consistent shift is observed from mechanisms and intermediates requiring big ensembles to mechanisms which can also operate on small ensembles. As a rule mechanisms involving big ensembles are faster. The identity of alloy components in their chemisorption and catalytic behaviour is preserved to a high extent also in alloys and is a more important feature in catalysis than the effects caused by mutual influencing of alloy components.
- Published
- 2010