EFFECT OF T(III) ZONING IN MFI-TYPE ZEOLITES ON THE ADSORPTION-ISOTHERM AND DIFFERENTIAL ENTHALPIES OF ADSORPTION AT 77-K

The characterization of MFI-type samples with crystals exhibiting eith er a homogeneous or heterogeneous distribution of the trivalent metal (aluminum or iron, labeled T(III)) is carried out using isothermal gas adsorption microcalorimetry (Ar, N2, and CO) coupled with quasi-equil ibrium adsorption volumetry at 77 K. It is found that, especially duri ng the ''fluid-like' to 'solid-like'' phase transition exhibited on th ese samples, carbon monoxide can distinguish those with a distinct T(I II) zoning (whether,it is toward the interior or exterior of the cryst als). Argon however, is not greatly affected by the T(III) content (wh atever the distribution) and provides a complementary textural examina tion of these samples.