Effects of ion-exchanged alkali metal cations on the photolysis of alkyl ketones included within ZSM-5 zeolite cavities: A study of ab initio molecular orbital calculations

摘要

Effects of ion-exchanged alkali metal cations on the adsorption and thernphotolysis (Norrish type I and type II reactions) of 2-pentanone included withinrnthe alkali metal cation-exchanged ZSM-5 zeolite have been investigated byrnexperimental and theoretical approaches. The yields of the photolysis decreasedrnand the ratio of the type I / type II reactions increased, respectively, by changingrnthe ion-exchanged cations from Cs~+ to Li~+. The observed IR spectra of thernadsorbed ketones and the ab initio molecular orbital calculations of this hostguestrnsystem indicate that the ketones interact with two different adsorptionrnsites, i.e., the surface OH groups and alkali metal cations, while the electrostaticrninteraction between the ketones and cations increases by changing the cationsrnfrom Cs~+ to Li~+. These approaches also indicate that the type I and type IIrnreactions proceed from the staggered and eclipsed conformations of 2-pentanone,rnrespectively, and that the smaller cation has the stronger electrostaticrninteraction between ketone and promotes the type I reaction of ketone efficiently.