Local structure of silver clusters in the channels of zeolite 4A

Abstract

The Ag K-edge EXAFS measurements have been carried out at 50 K for fully Ag+-exchanged zeolite 4A (Ag-4A) dehydrated at different temperatures under vacuum. In the Fourier transforms of the EXAFS oscillation the two distinct peaks appear around 2.2 Å and 3.0 Å, and a shoulder around 2.8 Å. The structural parameters (distance, coordination number and root mean square displacement) were derived by a three-shell (two Ag-O contacts and Ag-Ag contact) curve-fitting analysis. It is found that a silver cluster is formed with Ag-Ag distance 2.82±0.02 Å and coordination number 4.9±0.2. When the silver cluster is formed 6 Ag0 atoms and 8 Ag+ ions are arranged in a cubic closed-packed manner in the cage of the Ag-4A zeolite. The 8 Ag+ ions and 6 Ag0 atoms are confined in the framework of oxygens at distances of 2.28±0.02 and 2.88±0.02 Å, respectively.