The structure and activity of Pt6 particles in ZSM-5 type zeolites

Density functional theory was applied to investigate the nature of active sites formed by the interaction of a Pt6 guest particle with the silicalite and H-form of ZSM-5 as the host zeolites. Interaction of metal cluster with silicalite shows a slight stabilization (36kJ/mol) and formation of a negatively charged Pt entity. When a metal particle is arranged in the channel of H-form substantial stabilization (187kJ/mol) and generation of an oxidized Pt6H+ species are observed. The formation of an active site includes interaction between a platinum particle and an acid site accompanied by the suppression of zeolite acidity. The suggestion is made that the alkane transformation on supported platinum particles proceeds via metal–cyclobutane and metal–carbene intermediates and does not need the direct involvement of acid sites. The difference in catalytic behavior of the Pt6/HZSM-5 and Pt6/ZSM-5 systems is discussed.