Surface Analysis of a Hydrothermally Treated H-ZSM-5 Zeolite

✍ Scribed by Marschmeyer, Steffen; Papp, Helmut

• Publisher: John Wiley and Sons
• Year: 1997
• Tongue: English
• Weight: 342 KB
• Volume: 25
• Category: Article
• ISSN: 0142-2421
• DOI: 10.1002/(sici)1096-9918(199708)25:9<660::aid-sia279>3.0.co;2-7

✦ Synopsis

The external surface of a hydrothermally treated H-ZSM-5 zeolite was studied with XPS and x-ray Auger electron spectroscopy. It was established that Al removed from tetrahedral framework positions migrated into the outermost layers and produced an Al enrichment. In order to get information on the acidic properties of the outermost layers and of extra-framework Al (EFAl), we investigated the XPS N 1s level of adsorbed ammonia. Two di †erent Bro nsted acid sites with N 1s binding energies of 402.3 » 0.5 and 401.2 » 0.2 eV, respectively, were found in the untreated H-ZSM-5 zeolite. A third acid site (398.8 » 0.3 eV) appeared after water vapour treatment, which is probably also a Bro nsted acid site. The modiÐed Auger parameter aº was used for identiÐcation of the chemical state of EFAl. The removed Al maintained the tetrahedral coordination, was non-acidic, uncharged, partly soluble in concentrated acetic acid and able to block part of the acid sites. A comparison of acidity between the surface and bulk phase (temperature-programmed desorption results) clearly showed that Al is heterogeneously distributed in the framework. A large part of Al on the surface is not in a framework position and is blocked by EFAl. 1997