Interaction of Carbon Dioxide with Silver Zeolites

Abstract

Photooxidation of water to O₂ and of Cl^⊖ to Cl₂ by Ag^⊕-exchanged zeolite A is briefly reviewed. Thermodynamic considerations concerning the free energy storage during these reactions are given. Interaction of CO₂ with Ag^⊕-exchanged zeolite A of various Ag^⊕ content, in the original and partially reduced state, is probed by in situ FTIR transmission spectroscopy. Chemisorbed, carbonate-like species are found in samples of low silver content. The CO₂ physisorption capacity is lowest for highly Ag^⊕-exchanged samples. After removing the physisorbed CO₂ by evacuation, a small amount of weakly bound CO₂ remains in the zeolite. Its ν₃ (asymmetric stretching) frequency is cation dependent, reflecting some specific interaction with the cations. On chemical reduction of the Ag^⊕, the amount of weakly bound CO₂ markedly increases, accompanied by spectral changes of the ν₃ band of CO₂.