Detailed Electronic Structure of Octahedral Ag Clusters Confined in Zeolite A

Abstract

The properties of exchanged zeolites depend on the structure−guest relationship. The abundant work accumulated over the past few years reveals gaps in knowledge about this relationship,both experimental and theoretical. We studied in detail the electronic structure of fully Ag-exchanged dehydrated zeolite LTA by first-principles calculations involving the whole unit cell, that is, a nonsimplified structural model. The use of the large stoichiometric unit cell allowed us to study the role of intrinsic disorder on the electronic structure and its spectral signatures, in addition to the modulation of the electronic structure owing to the octahedral Ag clusters confined within the sodalite cage, to evaluate its charge state and to determine the spatial extent of the modulation. In addition, differences in the electronic structure due to changes in the size and structure of the confined Ag clusters were investigated. In this way, it was determined that the density of states has varying contributions of Ag atoms in the framework and the cluster. Because the electronic structure presents variations dependent on the coordination environment and, despite the extremely low stability of zeolites under an electron microscope, recent progress in instrumentation allows us to harbor enormous expectations that studies on the electronic structure and its modulation can be started and carried out with almost no radiation damage. In this context, we evaluate the potential efficacy of electron energyloss spectroscopy in distinguishing filled and empty sodalite cages and in sensing different Ag clusters.