Why In3+ is not isomorphously substituted into zeolite ZSM-5: reaction of ZSM-5 with aqueous InF3

It has been reported that In3+ is isomorphously substituted into the T-atom sites of zeolite ZSM-5 by hydrothermal crystallization in the presence of indium salts. It is reported here that attempts to insert In3+ into the ZSM -5 framework via secondary synthesis using aqueous InF3 were unsuccessful, whereas previous substitutions with other metal fluorides containing ions s uch as Si4+, Al3+, Be2+, and B3+ were possible using the same method. We hy pothesize that the In3+ ion is too large to be inserted into the T-atom sit e of ZSM-5 and suggest an alternate hypothesis, fully consistent with the a nalytical data, wherein the In3+ ion exists entirely in the form of amorpho us, highly basic indium oxides or hydroxides dispersed on high silica ZSM-5 crystals. (C) 2000 Elsevier Science S.A. All rights reserved.