FUNDAMENTAL DEFECT CENTERS IN ALPO4-5 AND VPI-5 MOLECULAR-SIEVES

For the first time, the formation of paramagnetic defect centers in Al PO4 molecular sieves has been monitored by electron spin resonance (ES R) spectroscopy. Results from ESR measurements demonstrate that the st ructural defects in hydrated AlPO4-5 and VPI-5 molecular sieves change into paramagnetic defect centers when the molecular sieves are dehydr oxylated under a high vacuum (similar to 10(-5) Torr) at 773 K. Adsorp tion of O-2 or NO on dehydroxylated molecular sieves causes an immedia te loss of the ESR signals from paramagnetic defects. This suggests th at the defect centers formed are F-type centers, which can serve as el ectron donors for electron-withdrawing adsorbates.