REVERSIBLE REDOX BEHAVIOR BETWEEN SILVER CATIONS AND SILVER METAL PARTICLES IN HYDRATED AG-Y ZEOLITES

Redox behaviour of Ag+ ions in Ag+-exchanged Y-zeolite (Ag-Y) has been investigated by the measurement of hydrogen consumption at 303 K, X-ray diffraction of Ag metal particles and IR spectra of CO chemisorbed on Ag+ ions. X-Ray diffraction gave evidence of the fully reversible interconversion between Ag+ ions and Ag metal particles upon introduction and withdrawal of hydrogen in Ag-Y partially reduced with hydrogen. The reversible variation of the amount of Ag+ ions was also observed by IR spectra of CO adsorbed on Ag+ ions. The reversibility was also confirmed by hydrogen adsorption experiments. The conversion of Ag metal particles back into Ag+ ions is enhanced by water molecules adsorbed on Ag-Y. The interconversion between Ag+ cations and Ag metal particles became partially reversible with increasing the degree of Ag+ ion reduction.