Transition-Metal Ion Exchange Using Poly(ethylene glycol) Oligomers as Solvents

Poly(ethylene glycol) oligomers have been found to be effective its alternative solvents for the ion exchange of Mn2+, Fe2+, and Co2+ into hydrated and dehydrated Zeolite X (Na80Al80Si112-O-384 center dot nH(2)O). When attempted in aqueous solutions, the exchange of these cations quickly leads to destruction of the zeolite structure within 1-2 exchange cycles. However, in PEG oligomer solvents, the structure can be maintained and exchanges of 48% (Co2+), 80% (Mn2+), and 91% (Fe2+) are observed after one cycle under hydrated conditions. When rigorous steps are taken to remove all water from the zeolite before exchange, absorption of the oligomers into the zeolite pores is promoted, which hinders ion exchange: a maximum of 6% exchange is seen under dehydrated conditions. However, improved catalytic efficiency toward NO decomposition is observed for these samples, with turnover frequencies of 0.0237 s(-1) for Dehyd Na/Mn-X oligomer, 0.0213 s(-1) for Dehyd Na/Fe-X oligomer, and 0.0190 s(-1) for Dehyd Na/Co-X oligomer. Use of these PEG oligomers as reaction media has also been expanded to the ion exchange of layered oxides such as Dion-Jacobson perovskite phases.