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

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 v acuum. In the Fourier transforms of the EXAFS oscillation the two distinct peaks appear around 2.2 Angstrom and 3.0 Angstrom, and a shoulder around 2. 8 Angstrom. The structural parameters (distance, coordination number and ro ot mean square displacement) were derived by a three-shell (two Ag-O contac ts and Ag-Ag contact) curve-fitting analysis. It is found that a silver clu ster is formed with Ag-Ag distance 2.82+/-0.02 Angstrom and coordination nu mber 4.9+/-0.2. When the silver cluster is formed 6 Ag-0 atoms and 8 Ag+ io ns are arranged in a cubic closed-packed manner in the cage of the Ag-4A ze olite. The 8 Ag+ ions and 6 Ag-0 atoms are confined in the framework of oxy gens at distances of 2.28+/-0.02 and 2.88+/-0.02 Angstrom, respectively.