Fe and B substitution in ZSM-5 zeolites: A quantum-mechanical study

✍ Scribed by A. Chatterjee; A.K. Chandra

• Publisher: Elsevier Science
• Year: 1997
• Tongue: English
• Weight: 560 KB
• Volume: 119
• Category: Article
• ISSN: 1381-1169
• DOI: 10.1016/s1381-1169(96)00468-2

✦ Synopsis

Density functional theory has been used to study isomorphous substitution of Fe and B for Si in orthorhombic MFI type zeolite ZSM-5. Calculations were performed on monomer [TV], dimer [(OH),-Si-0-T-(OH),] and pentamer T(OSiO,H,), cluster models where T = Fe or B. It has been experimentally observed that Bronsted acidity of substituted ZSM-5 increases in the order B-ZSMS < Fe-ZSM-5 K Al-ZSM-5. Although change in acidic properties with substitution is known, the position of framework substitution with Fe and B in ZSM-5 has not yet been established. In the present work, we have done detailed density functional calculations to find out the site of framework substitution with Fe and B in ZSM-5.

We have observed that the calculated properties display a substantial size dependence on the size of the model. Our calculations suggest that the preferable siting for Fe is 3 and 11 and for B it is 2 and 12 in ZSM-5 zeolite framework.