ISSN:
1572-879X
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
Notes:
Abstract Density functional theory calculations have been carried out to establish the influence of mono- and polyvalent cations on the Brønsted acidity of H-ZSM-5. The zeolite was modeled as a cluster containing 41-45 atoms, in the center of which is an Al(1)(OH)SiOAl(2)(OM)unit, where M+ = H+, Li+, Na+, K+, Ca(OH)+, AlO+, Al(OH)+ 2. The local geometry of the Brønsted acid site is affected by the nature of M+ and this in turn causes a change in the value of the proton affinity (PA) for the site. The highest value of PA is 330 kcal/mol for M+ = H+ and the lowest value of PA is 305 kcal/mol for M+ = AlO+. No correlation was found between the value of PA and the Mulliken charge on Al(1). With the exception of the case where M+ = AlO+ the binding energy of CO with the Brøsted acid proton is approximately 8.8 kcal/mol, independent of the nature of M+. When M+ = AlO+, the binding energy for CO is 11.1 kcal/mol. The present calculations suggest that different factors affect proton affinity and the binding energy for CO adsorption.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1023/A:1019095808885
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