Understanding the role of zeolite A-supported Cu and Ag nanospecies in ethylene adsorption

GONZALEZ, M. R.; M. S. MORENO; A. AVILA; MARIA S. LEGNOVERDE; NICOLA GARGIULO; D. MONZÓN,; D. CAPUTO; ANDREA PEREYRA; BASALDELLA, E.

CABA

Congreso; 11th World Congress of Chemical Engineering.; 2023

Asociación Argentina de Ingenieros Químicos

Ethylene scavengers are important in technologies for the preservation of flowers, fruits, and vegetables, to extend the storage life of the products. The lowering of the ethylene concentration by selective adsorption is essential to slow down the maturation process during the packing and transportation of the harvested products. Zeolitic structures are widely recognized for their ability to host and stabilize positively charged species, and also for providing controlled aggregation of nanosized metals. The specific properties of transition metal-doped zeolites arise from the variations of the chemical state and position of the entities dispersed in the matrix. The control of the chemical nature, nuclearity, and oxidation state of metallic species confined in porous materials plays an important role according to the technological application. Clusters of different nuclearity within the structural cages of metal-exchanged zeolites could be produced by thermal activation, providing versatile and interesting attributes related to luminescent properties, selective oxidation-reduction conditions, etc. Concerning adsorption processes, Cu or Ag-doped materials have been extensively used for the selective retention of light olefin from different olefin/paraffin mixtures [1]. The mechanism involves the interaction of olefin orbitals with the empty d orbital of cation, in a process denominated π-complexation. Among the wide number of related technological applications, this property allows the use of doped zeolites for the ethylene adsorption in the atmosphere generated when fruits are collected and storage.In this study, Cu and Ag-Zeolite-based adsorbents were prepared to investigate the nature of the species present in the structure and its correlation with their adsorption capacity and affinity towards ethylene. Na+ in NaA zeolite was replaced with Ag+ or Cu+ by varying the salt concentration in the aqueous solutions. The exchanged zeolites were thermal treated at different temperatures and times of exposition in an N2 atmosphere. The XRD, UV–Vis, and HRTEM analyses indicated that thermal treatment could induce framework distortion and reordering of the original M+ into different species (metallic or oxide nanoparticles, nanoparticulate aggregates, and intraframework Mmn+ clusters). Ethylene adsorption isotherms show a higher adsorption capacity for Ag-doped zeolites. In an overall analysis, the highest adsorption capacity and affinity towards ethylene were obtained for the samples containing mainly metallic cations and reoxidizing species that better promote π interaction. The increase of M+ loading in heat-treated zeolite did not improve olefin adsorption. Nevertheless, at low pressure, these samples showed good affinity towards ethylene. Despite presenting inactive nanoparticles against olefin, the high content of accessible charged species remnants even after high-temperature treatment could be responsible for the improved ethylene adsorption.