H-ZSM-5 samples were pretreated with dilute NaOH and then transformed
into the acid state. The variation of framework Al was studied by Al-2
7-MAS-NMR spectroscopy, the Al gradient by XPS and the OH groups by IR
spectroscopy. The catalytic activity was studied in the conversion of
propane and of methanol. The treatment of the parent zeolite (5.2 Al/
u.c.) resulted in a slight decrease of the content of framework Al but
in a strong enrichment of nonframework Al on the outer surface. The c
atalytic effect was an increased aromatization of propane and a prolon
ged lifetime in the methanol conversion. The treatment of a dealuminat
ed sample, containing much nonframework Al, caused a partial reinserti
on of Al into the framework. This modification leads to an enhanced ar
omatization of methanol. Thus treatment with NaOH can control the cont
ent of framework Al and the catalytic activity, selectivity, and stabi
lity. (C) 1994 Academic Press, Inc.