The stability of nanosized HZSM-5 zeolite: a high-resolution solid-state NMR study

The thermal and hydrothermal stabilities of HZSM-5 zeolites with crystal si zes less than 100 nm have been studied by multinuclear solid-state NMR, com bined with BET and XRD. As evidenced by Al-27 and Si-29 MAS as well as thei r corresponding cross-polarization/MAS NMR investigations, the thermal stab ility of nanosized HZSM-5 is not so good as that of microsized HZSM-5. This is due to two processes concerning dealumination and desilicification invo lved in the calcination of nanosized HZSM-5, while only the dealumination p rocess is conducted in microsized HZSM-5 under the similar calcination proc ess. The hydrothermal stability of nanosized HZSM-5 is, contrary to what wa s expected, not so bad as that of the microsized HZSM-5 in the course of st eam treatment. The actual resistance of the hydrothermal stability to the c rystal size of HZSM-5 can be ascribed to an active reconstruction of zeolit ic framework through an effective filling of amorphous Si species into nano sized HZSM-5 during hydrothermal treatment. (C) 2001 Published by Elsevier Science B.V.