Structural Characterization of Metal Ions Incorporated in Molecular Sieve Frameworks

Abstract

Isomorphous and non‐isomorphous substitutions of transition metal and IIIA elements for framework atoms of molecular sieves are very interesting in order to modify their acidic and redox catalytic properties. In this paper, we review the interaction between metal cations other than Al+3 with zeolitic frameworks in Ti, Co, V and Ga‐containing silicate and aluminophosphate zeolites detected by spectroscopic investigations. During synthesis and redox treatments, solvent, oxidant and surface silanol groups sometimes were found to attach to the framework metal ion sites, perhaps involved in the variation from tetrahedral to non‐tetrahedral coordinations.

Structure of the Catalytic Active Sites in Vanadium-Doped Aluminophosphate Microporous Materials. New Evidence from Spin Density Studies

“…Finally, depending on the synthesis conditions, vanadium may adopt different coordination numbers. 38 The combination of these factors makes the characterisation of V in AlPO, and hence "mapping" its behaviour, a difficult task for both experimental and computational studies. 39 In this work, the structure of V ions in VAPO-5 is investigated by means of a combination of 27 Al ligand hyperfine interactions (hfi), which are measured by means of HYSCORE spectroscopy at X-and Q-band frequencies.…”

“…Furthermore, V ions in solution can give rise to oligomerization and yield polynuclear clusters. Finally, depending on the synthesis conditions, vanadium may adopt different coordination numbers . The combination of these factors makes the characterization of V in AlPO, and hence “mapping” its behavior, a difficult task for both experimental and computational studies …”