Ferrisilicate analogs of ZSM-11

✍ Scribed by J.S. Reddy; K.R. Reddy; R. Kumar; P. Ratnasamy

• Publisher: Elsevier Science
• Year: 1991
• Tongue: English
• Weight: 513 KB
• Volume: 11
• Category: Article
• ISSN: 0144-2449
• DOI: 10.1016/s0144-2449(05)80004-1

✦ Synopsis

Crystalline

ferrisilicate analogs of ZSM-11, free of ZSM-5 impurities, have been synthesized and characterized.

The results obtained by various spectroscopic techniques (XRD, MAS n.m.r., e.s.r., framework i.r.), magnetic susceptibility, thermal analysis (d.t.a./t.g.), adsorption, ion exchange, and catalytic measurements provide convincing evidence for the presence of iron in the zeolite framework. The ferrisilicate FeZSM-11 was free of Al (Si02/A1203 > 4000). There was an increase in the lattice constants and volume on incorporation of Fe. The white color of the as-synthesized and calcined samples as well as the magnetic susceptibility values @I = 5.5-5.8 EM) indicate that the Fe3+ ions tire present in a dispersed, magnetically dilute environment.

The Miissbauer isomer shift value, 6 = 0.23 at 297 K, and an e.s.r. signal at g = 4.3 suggest the presence of Fe3+ . Ions in a tetrahedral symmetry. The adsorption capacities exhibited by FeZSM-11 and AIZSM-11 were comparable. The significant catalytic activity of ferrisilicates in m-xylene and ethylbenzene conversions, due to Briinsted acid sites, indicates the presence of iron in framework positions. Though HFeZSM-11 is less active than is HAIZSM-11, the former is more resistant toward deactivation.