In- and Ga-oxo clusters/hydrides in zeolites: speciation and catalysis for light-alkane activations/transformations

Abstract

Metal-exchanged zeolites have great potential to form unique active metal species and develop their catalysis by promoting small molecules such as light alkanes. Ga-exchanged zeolites have attracted attention as promising heterogeneous catalysts for dehydrogenative light-alkane transformations. The speciation of active Ga species in reduced and oxidized Ga-exchanged zeolites and their reaction mechanisms have been discussed in several studies based on experimental and theoretical investigations. In contrast, studies on In-exchanged zeolites have been far less explored, and thus active In-species have rarely been investigated. In this perspective, we summarized our investigations on In- and Ga-exchanged zeolites for light-alkane transformations. Our research group reported the formation of In–oxo clusters using the O₂ treatment of In-CHA and their potential for the partial oxidation of CH₄ (POM) at room temperature. We also observed the formation of In-hydrides in CHA zeolites during the preparation through reductive solid-state ion-exchange (RSSIE) and revealed their catalysis for non-oxidative C₂H₆ dehydrogenation (EDH). Their detailed structures and reaction mechanisms are discussed in combination with spectroscopic, kinetic, and theoretical studies. Furthermore, comparative studies on the formation of Ga-oxo clusters for POM at room temperature and the controlled formation of Ga-hydrides for selective EDH were conducted. The obtained results and insights are comprehensively discussed, including the relationship between the local structure of the active In/Ga species and reaction selectivity, as well as the influence of different zeolite frameworks on the formation of active species.