Redox behaviour of transition metal ions in zeolites. Part 5.—Method of quantitative determination of bidisperse distributions of metal particle sizes in zeolites

Abstract

Temperature programmed reduction and oxidation techniques were used as a fast and quantitative method to determine the amount transition metal inside or outside the zeolite after a reductive treatment. The method has been applied to Ag, Cu and Ni and to different zeolites—X, Y, Z and L.

For Ag and Cu zeolites it was found that small metal particles located in the zeolite cages show a low temperature maximum in the rate of oxidation. The maximum in the rate of reoxidation of the metal phase outside the zeolite is found at distinctly higher temperatures. For Ni zeolites, the determination of the bidisperse metal distribution requires first a complete reoxidation of the sample. During a subsequent reduction, two metal dispersions can be distinguished on the basis of maxima observed in the rate of reduction.