Incorporation of cationic indium species into zeolite beta by template-induced reductive solid-state ion exchange

Abstract

Reductive solid-state ion exchange (RSSIE) was found to proceed in mechanical mixtures of crystalline In₂O₃ and as-synthesized precursors of zeolite beta (TEA-beta) during thermal decomposition of the template (TEA) in an inert gas atmosphere or high vacuum. It was evidenced that gaseous decomposition products of the template play the decisive role as reductants in this process, which results in the incorporation of univalent indium cations into the zeolite structure. Accordingly, no reaction between In₂O₃ and the zeolitic component was observed during template decomposition in an oxidizing atmosphere. After RSSIE associated with thermal template decomposition both In⁺ and InO⁺ lattice cations could be detected by typical IR spectroscopic bands attributed to interactions of these ions with adsorbed pyridine. The trivalent indium species are probably formed by a redox process involving the reduction of protons (internal silanol groups) to H₂ and oxidation of In⁺ into InO⁺. In line with this conclusion is the finding that part of the In⁺ cations are converted into InO⁺ upon contact with water.