Characteristics of Proton Hopping in Zeolite H-ZSM5

✍ Scribed by M.E. Franke; U. Simon

• Publisher: John Wiley and Sons
• Year: 2000
• Tongue: English
• Weight: 152 KB
• Volume: 218
• Category: Article
• ISSN: 0370-1972
• DOI: 10.1002/(sici)1521-3951(200003)218:1<287::aid-pssb287>3.0.co;2-8

✦ Synopsis

The hopping of protons in the anionic framework of zeolite H-ZSM5 with different SiO 2 /Al 2 O 3 ratios was examined by complex impedance spectroscopy. We found that the activation energy for the hopping process depends on the spatial distance between the localization sites, given by the SiO 2 /Al 2 O 3 ratio, according to classical hopping transport theory.

Zeolites are nanoporous crystalline, hydrated alumosilicates, the general formula of which is

. They consist of an open threedimensional framework structure of SiO 4 and AlO À 4 edge sharing tetrahedra (Fig. 1) wheras each negative charge of an AlO À 4 tetrahedron is typically compensated by an exchangeable metal cation like Na + or K + .

Generally, zeolites exhibit no electronic conductivity, since they reveal a wide electronic band gap of approximately 7 eV [2]. Instead most of them are ionic conductors, M. E.