Investigation of the coordination state of aluminum in beta zeolites by X-ray photoelectron spectroscopy

beta zeolites have been characterized by X-ray photoelectron spectroscopy (XPS). Owing to the small crystallite size (20 nm), nearly 90% of the Si and Al content can be estimated from the Si 2p and Al 2p peaks. The chemical state of Al was established by decomposition of the Al KLL Auger transition. Three types of Al could be differentiated: tetrahedral (Al-IV), octahedral (Al-VI), and tricoordinated (Al-III). From the decomposition of the Al KLL peak of a beta zeolite calcined to remove its template, it was found that Al-IV transforms to Al-III and Al-VI. Reversibility of Al-III to Al-IV also occurred when the sample was ammonium-exchanged, confirming Al-27 MAS NMR results.