A calorimetric investigation of CO, N-2, and O-2 in alkali-exchanged MFI

We have examined the adsorption of CO, N-2, and O-2 at 195 K in siliceous M FI (silicalite) and Li-, Na-, and K-exchanged MFI using microcalorimetry. T he differential, isosteric heats demonstrate that CO and N-2 interact stron gly with cations, while isosteric heats for O-2 were not affected by the pr esence of the cations. The zero-coverage heats for CO and N-2 decreased wit h increasing size of the alkali cation. On Li-MFI, the differential heats d ropped to the value observed on silicalite at coverages only slightly above the site density for Li. In contrast, the heat profiles on Na-MFI and K-MF I suggest that more than one molecule can interact with a single cation. Th e implications of these results for characterization of adsorbents are disc ussed. (C) 2000 Elsevier Science B.V. All rights reserved.