ADSORPTION BY MFI-TYPE ZEOLITES EXAMINED BY ISOTHERMAL MICROCALORIMETRY AND NEUTRON-DIFFRACTION .2. NITROGEN AND CARBON-MONOXIDE

Physisorption of nitrogen and carbon monoxide on a series of MFI-type zeolites with varying Si/Al ratios was examined by isothermal volumetry and microcalorimetry with reference to a neutron diffraction study of nitrogen adsorption on silicalite-I. The adsorption of both molecules occurs by site. For samples with a high Si/Al ratio (>120), two adsorbate phase transitions could be distinguished for both adsorptives, corresponding to a ''disordered phase'' (presumably a fluid) to ''lattice fluidlike'' and then to a ''crystalline-like solid phase''. The former transition was indistinguishable for the other samples; however the latter was observed at lower pressures and more diffuse with decreasing Si/Al ratio.