Ethylene adsorption onto thermally treated AgA-Zeolite

Abstract

Ag-Zeolite-based adsorbents were prepared in order to investigate the nature of the Ag species present in the zeolite structure and its correlation with their adsorption capacity and affinity towards ethylene. Na+ in NaA were partially replaced with Ag+ by ion exchange in aqueous media. By varying the AgNO3 concentration used in the aqueous solutions, two dissimilar Ag+ exchange levels were obtained. The exchanged zeolites were thermally treated at 90 ºC for 12 h and at 350 ºC for 4 h in N2 atmosphere. The X-ray diffraction (XRD), UV-visible (UV-Vis), and high-resolution transmission electron microscopy (HRTEM) analyses indicated that thermal treatment could induce framework distortion and reordering of the original Ag+ cations into different Ag species (Ag and Ag2O nanoparticles, nanoparticulate aggregates and Agmn+ clusters). The increase of both silver load and temperature diminished the adsorbed amount. The highest adsorption capacity and affinity towards ethylene were obtained for the sample containing the silver species that better promote 5s1<-->p interactions. Nevertheless, at low pressure, samples with a high silver content and treated at 350 °C showed a good affinity towards ethylene. Despite presenting inactive nanoparticles against olefin, the high content of accessible charged species could be responsible for the improved ethylene adsorption.