SILVER ZEOLITE-MODIFIED ELECTRODES - ELECTRON-TRANSPORT MECHANISM ANDION-EXCHANGE KINETICS FOR PARTIALITY SILVER EXCHANGED ZEOLITE-Y

The pseudo-first-order rate constants For ion exchange of partially si lver ion exchanged Y zeolites (AgnNa56-nY) with sodium ions are determ ined from chronoamperometric studies of zeolite-modified electrodes in aqueous solution. In the case of AgnNa56-nY when n less than or equal to 5.9 the electrochemical reduction of intrazeolite Ag+ cations is c ontrolled by an intracrystalline ion-exchange process rather than by c ounterdiffusion of exchanging cations through the interconnected super cage system of the zeolite. Herein the methodology for analysis of thi s situation is developed where the rate of the electrochemical reactio n is equated with the velocity of the rate-limiting ion-exchange react ion. Good agreement between theory and experiment was observed. The ps eudo-first-order rate constant for Ag+ exchange with Na+ is relatively insensitive to the concentration of sodium in the electrolyte solutio n, but decreases as the silver loading in the zeolite is increased up to 5.9 silver ions per unit cell. The data are consistent with electro n transfer to silver ions occurring subsequent to the ion-exchange ste p, confirming once again that electron transfer occurs outside of the zeolite framework.