Change in pore structure of MFI zeolite by treatment with NaOH aqueous solution

Changes of the pore size and the pore volume of MFI zeolite (Si/Al = 37) upon treatment with an NaOH aqueous solution (0.05 mol dm(-3)) have been investigated at the temperature range from 323 to 343 K by means of adsorptions of Ar and N-2. The total surface area (BET surface area) increased at the initial stage of the treatment and then decreased slowly. The change of the total surface area was attributed to that of the external surface area. BJH analysis of the N-2 adsorption isotherm revealed that the supermicropores having a width of about 1.8 nm were created by the treatment of NaOH. In addition, Saito-Foley analysis of the Ar adsorption isotherm showed that the size and the volume of the micropores remained almost unchanged after the NaOH-treatment. It was evident from elemental analysis that about 30% Si of the MFT zeolite was dissolved by the treatment, while only a few percent of Al was released. These results demonstrate that the framework of the crystalline phase was stable against the NaOH-treatment and probably the amorphous phases present at the boundary of the crystallites dissolved to form the supermicropores, supporting a previous report [Chem. Lett. (2000) 882]. (C) 2001 Elsevier Science B.V. All rights reserved.