Siting and coordination of cobalt in ferrierite: XRD and EXAFS studies at different Co loadings

• Published in: Microporous and mesoporous materials 2003-08, Vol.62 (3), p.191-200
• Main Authors: Dalconi, M.C., Alberti, A., Cruciani, G., Ciambelli, P., Fonda, E.
• Format: Article
• Language: English
• Subjects: Chemistry; Co 2+ ions; Exact sciences and technology; Ferrierite; General and physical chemistry; Ion-exchange; Metal ion-exchanged zeolite; Rietveld refinement; Surface physical chemistry; Zeolites: preparations and properties
• ISSN: 1387-1811; 1873-3093
• DOI: 10.1016/S1387-1811(03)00404-9

The crystal structure of three synthetic ferrierite samples loaded with different amounts of Co cations (2.5 wt.%, 4.3 wt.% and 13.7 wt.% respectively) were refined by means of synchrotron X-ray powder diffraction data. The unit cell content of cobalt exchanged ferrierites resulted: ∣Na 0.18K 0.03Co 1.12H 1.36(H 2O) 17.2∣[Al 3.81Si 32.19O 72]–– FER, ∣Na 0.18K 0.03Co 1.89(H 2O) 17.2∣[Al 3.81Si 32.19O 72]–– FER, and ∣Na 0.18K 0.03Co 1.89(H 2O) 17.2∣[Al 3.81Si 32.19O 72]–– FER respectively. In the overloaded sample the excess of Co (9.4 wt.%) is located outside the zeolite structure as cobalt oxide phases. After cation exchange the space group, which was P2 1/ n in the as-synthesised form, becomes Immm. The crystal structure of the three synthetic samples is characterised by the presence of a Co(H 2O) 6 2+ polyhedron inside the ferrierite cage. The occupancy of this polyhedron varies as a function of the Co amount in the extra-framework sites of the ferrierite structure: up to 50% for a complete ion-exchange. The residual cobalt occupies two further cation sites.