A density functional study of CO adsorption on three- and five-coordinate Al in oxide systemsстатья
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Дата последнего поиска статьи во внешних источниках: 18 июля 2013 г.
Аннотация:Conventional cluster models of strong and medium strength Lewis acid sites in alumina and zeolites, three-coordinate [Al(OH)3] and five-coordinate [Al(OH)3(OH2)2] respectively, are studied with the help of a density functional method. A constraint space orbital variation analysis reveals that the charge transfer from probe CO molecules adsorbed on cationic Al centre and the CO polarization comprise essential contributions to the adsorption energy De. An analysis of the adsorption-induced C-O frequency shift Δω(C-O) is also provided. Structural modifications of the Lewis acid sites are considered with respect to their influence on De and Δω(C-O). A comparison of the measured and calculated C-O frequency shifts supports a hypothesis on the existence of Lewis acid sites in oxides in the form of four-coordinate Al cations.