A mechanistic study of the solid-state reactions of H-Mordenite with Indium(0) and Indium(III)oxide

Abstract

Solid-state reactions of In2O3/H-mordenite and In0/H-mordenite mixtures (Al/In = 3) were studied using an atmospheric flow-through microreactor, diffuse reflectance Fourier-transform spectroscopy (DRIFTS), and X-ray powder diffractometry (XRD). The indium(III)oxide/H-mordenite mixture was heated in a flow of 2% H2/N2 gas mixture or pure N2 to 873 and 973 K, respectively. The indium(0)/H-mordenite mixture was heated in a dry and wet N2 stream to 673−973 K. The reactions were monitored by analyzing the effluent gas, using mass spectroscopy (MS). The protons of H-mordenite were exchanged for In+ cations, indicating that In3+ was reduced and In0 was oxidized in the exchange processes. In the process of reductive solid-state ion exchange (RSSIE), the indium was reduced by H2. In the oxidative solid-state ion exchange (OSSIE) process, the indium was oxidized by H2O. Results substantiate that the ion exchange proceeds through a volatile InOH intermediate. Formation of InOH and its rapid transport within the zeolite crystals requires the presence of water vapor. The In+ in the zeolite lattice can be oxidized by O2 or H2O to indium oxycations, most probably to InO+, while the obtained oxycations can be reduced in hydrogen back to In+.