Growth and reactivity of zinc and cadmium oxide nano-particles in zeolites

Zinc and cadmium oxide particles in the size range of 1-10 nm grow inside a faujasite matrix, zeolites X and Y or its hexagonal analogue EMT starting from metal ion-exchanged zeolites subjected (i) to sodium hydroxide solutions (0.01-0.75 M) at elevated temperatures (293-353 K) and (ii) to subsequent calcination in air at 673 K. The oxide nano-particles are accommodated in mesopores forming simultaneously with the precipitation of the metal hydroxides. As revealed by adsorption measurements the maximum diameters and the overall volumes of the mesopores grow with increasing concentration of the lye used for the precipitation. The main portion of mesopores is formed as bubbles inside the zeolite matrix, only a small fraction as pockets at the outer surface of the zeolite crystallites. The embedded oxide nano-particles are physically and chemically uniform, i.e. they show (i) the expected quantum size effects in the diffuse reflectance spectra and (ii) a particle size effect concerning the reversible formation of cadmium carbonate.