Study of the activation of C-H and H-H chemical bonds by the [ZnOZn]2+ oxycation:: Influence of the zeolite framework geometry

The reactivity of the [ZnOZn](2+) oxycation, located inside the zeolite micropores, has been studied by the periodical density functional method. Two different types of rings, six- and eight-membered, have been used as hosts for this cation. In addition, within each of these ring structures the arrangement of the two aluminum atoms has been explored, generating different configurations. Two different probe molecules have been used in this investigation: methane and molecular hydrogen. Both molecules prefer to chemisorb on this active site. Their dissociation reactions are strongly influenced by the surrounding zeolite environment and by the Al distribution within the zeolite ring framework. The [ZnOZn](2+) cation is able to activate both C-H and H-H bonds, particularly the latter one. These results are in line with previous calculations and recent experimental results. They also confirm that this active site is present in high-silica zeolites. However, this species seems unlikely to be the catalytic site for the alkane dehydrogenation.