CHARACTERIZATION BY INFRARED AND NUCLEAR-MAGNETIC-RESONANCE SPECTROSCOPIES OF CALCINED BETA-ZEOLITE

A beta-zeolite with template has been calcined in air at 550-degrees-C using two different experimental procedures. IR and Si-29 magic-angle spinning nuclear magnetic resonance (MAS NMR) spectroscopies showed t hat the extent of framework dealumination and the number of Bronsted a cid sites were greatly affected by the conditions of treatment. With s hallow-bed calcination, framework-Al extraction was limited but revers ible openings of framework Si-O-Al linkages were observed. The amount of extra-framework species increased with deep-bed calcination. Al-27 NMR results confirmed that the appearance of octahedral Al in protonic beta-zeolite does not necessarily involve framework-Al extraction. Ac id strengths were evaluated by pyridine adsorption-desorption cycles. The splitting of the band of Lewis-bonded pyridine at 1455 cm-1 at tem peratures higher than 350-degrees-C was shown to be due to adsorbate m odifications rather than irreversible structural changes of the solid.