Silver-exchanged CHA zeolite as a CO2-resistant adsorbent for N2/O2 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 CO 2 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 δ+ ) within the CHA framework upon activation under a dynamic vacuum of 10 −3 Torr at 523 K. The intrazeolitic formation of these Ag n δ+ clusters, whose ability to form π-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. • Ag + -exchanged zeolites with different framework topologies and Si/Al ratios are studied in N 2 /O 2 separation. • Ag-CHA-6.0 shows comparable N 2 /O 2 separation performance with commercial Li-X. • Ag-CHA-6.0 exhibits higher resistance to CO 2 than Li-X. • Partially charged silver clusters in Ag-CHA-6.0 contribute to its excellent N 2 /O 2 separation.