FT-IR Study of Carbon Monoxide Adsorption on Li-Exchanged Zeolite X

Abstract

Carbon monoxide adsorption on LiX-1.0 zeolite ([Li 9 6 .(Si 9 6 Al 9 6 O 3 8 4 )]-FAU, Si/Al = 1.0) has been studied by means of FT-IR spectroscopy at a wide temperature range (77-298 K) to investigate the nature and properties of the adsorption sites. We show the existence of two slightly different adsorption centers (Li + cations at sites SIII and SIII') in LiX-1.0 zeolite at room and low temperatures. Variable-temperature experiments confirmed that a phase transition from a cubic phase at ambient temperature to an orthorhombic phase at low temperature takes place between ∼220 and ∼235 K. Our studies indicate that cation redistribution takes place in this temperature range. The number of the Li + cations accessible for CO adsorption (most probably at site SIII') is increased significantly. We argue that this change in population of these sites is triggered by the presence of admolecules, as it is not observed in an unloaded adsorbent. The effective electric fields created by Li + cations at different sites in the cavity of LiX-1.0 zeolite are reported.