Co2+ ion siting in pentasil-containing zeolites II.: Co2+ ion sites and their occupation in ferrierite.: A VIS diffuse reflectance spectroscopy study

VIS-MR diffuse reflectance spectra of Co2+NaK- and Co2+H-ferrierites with Co loadings varying from 0.12 to 3.62 wt.% were studied. Three different coordinations of the Co2+ ions in Co-ferrierites dehydrated at 770 K were reflected in optical spectra, and their population depending on the Co ion concentration in both CoNaK- and CoH-ferrierites was determined. Site B is formed by four oxygens in a rectangle on the wall of the main ferrierite channel. The Co ions at this site, alpha type, are characterized by a band at 15 000 cm(-1). With increasing Co concentration the population of the Co2+ ions in site B increases for CoH-ferrierite and significantly decreases for CoNaK-ferrierite. The Co2+ ion of the type beta, located in site G of the ferrierite cavity, is characterized by absorption bands at 16 000, 17 100, 18 700 and 20 600 cm(-1). The Co2+ ion is coordinated to framework oxygens of the deformed six-membered ring. These Co2+ ions predominate in both CoH- and CoNaK-ferrierites. Two bands at 20 300 and 22 000 cm(-1) represent gamma-type Co2+ ions in a 'boat shaped' site C of the ferrierite cavity. The number of coordinated framework oxygens and detailed geometry of this site is not known. The Co2+ ions in this site represent a minority of Co2+ ions located in ferrierite. (C) 1999 Elsevier Science B.V. All rights reserved.