Study of the Fe/zeolite-L system -: Part II:: CO and H2 chemisorption behavior

The chemisorption properties of two solids, called Fe/ZLK and Fe/ZLH were studied. The samples were obtained by dry impregnation of potassic and acidic forms of zeolite-i with a ferric salt, as described in Part I. The adsorption isotherms of CO at 193 K and H-2 at 673 K were measured. ''In situ'' Mossbauer spectroscopy (MS) at 298 and 193 K of the reduced solids with chemisorbed CO allowed to confirm the preferential location of the Fe2+ exchanged with the support in both samples, in agreement with that obtained in Part I: sites i for Fe/ZLK and sites A for Fe/ZLH. The CO chemisorption resulted in an inappropriate method to obtain the metallic area of reduced Fe/ZLK, since Fe2+ ions in sites D also chemisorb, CO with a 1:2 = Fe2+:CO stoichiometry. In order to obtain the amount of Fe-0 surface atoms, H-2 chemisorption at 673 K in 10-80 Ton pressure range was successfully used. Combining this technique with MS, it was possible to determine the values of the Fe-0 crystal diameters. (C) 2000 Elsevier Science B.V. All rights reserved.