Microcalorimetric measurements were performed at 195 K for CO and N-2 On ze
olite H-MFI and on a siliceous MFI in order to characterize the interaction
of these molecules with the Bronsted acid sites. On the siliceous MFI, the
differential enthalpies of adsorption (isosteric heats) for CO and N2 were
found to be essentially constant with coverage at a value of 16 +/- 1 kJ/m
ol. While the isosteric heats for Nz were slightly higher on H-MFI at cover
ages below one per site, the additional interaction with the Bronsted sites
is less than 3 kJ/mol. For CO on H-MFl, microcalorimetry provides evidence
for a 1:1 adsorption complex with the acid sites in that the isosteric hea
ts are higher on H-MFI at low coverages and approach the values for the sil
iceous material at higher coverages. Because the calorimetric data can be f
it to a two-site, Langmuir model in which the hydrogen-bonded CO interacts
with an additional 10.5 KJ/mol, the results suggest that the Bronsted acid
sites in H-MFI are essentially identical in regard to how they interact wit
h CO.