Stability of Ti in MFI and Beta structures: a comparative study

The structural stabilities of TS-1 (Ti-MFI) and Ti-Beta zeolites after expo sure to aqueous H2O2 (30% w/w) have been examined by X-ray diffraction and spectroscopic methods (W-vis, IR and Si-29 MAS NMR). The catalytic properti es of these molecular sieves are dependent on the stability of Ti(IV) in th e framework. TS-1 was confirmed to be stable towards H2O2 solution, in agre ement with its well-known catalytic applications (e.g. hydroxylation, epoxi dation, ammoximation). Ti-Beta is not stable. Physical studies confirm the partial hydrolysis of titanium during H2O2 treatments with formation of hig hly defective situations and Ti movement to extraframework positions during the following calcination. Hence, dramatically different catalytic behavio rs and lifetimes are expected for these two catalysts. (C) 1999 Elsevier Sc ience B.V. All rights reserved.