Silver-exchanged CHA zeolite as a CO2-resistant adsorbent for N-2/O-2 separation

Abstract

Zeolite Li-X is considered the best adsorbent for air separation (i.e., N-2/O-2 one). However, this zeolite adsorbent suffers from serious limitations of preparation and process operation. Here, we report that Ag+-exchanged chabazite (Ag-CHA-6.0) with a Si/Al ratio of 6.0 shows comparable N-2/O-2 separation performance, but higher CO2 resistance than Li-X under N-2/O-2 simulated conditions. The characterization results reveal that its excellent separation performance may be due to the preferential formation of partially charged silver clusters (Ag-n(delta+)) within the CHA framework upon activation under a dynamic vacuum of 10(-3) Torr at 523 K. The intrazeolitic formation of these Ag-n(delta+) clusters, whose ability to form pi-complexation with N-2 is higher than monovalent silver ions, was found to depend not only on the structure type of the zeolite support, but also its framework Si/Al ratio.