Characterization of the Structural and Surface Properties of a Synthesized Hydrous Hollandite by Gaseous Molecular Adsorption

The structural and surface properties of a hydrous hollandite-type manganese oxide (H−Hol) were examined by adsorption using different gases with molecular diameters below 0.4 nm. N 2, O 2, Ar, CO, and CO 2 with diameters above 0.33 nm are excluded from the tunnel structure of H−Hol, whereas H 2 O and NH 3 with diameters below 0.265 nm can be inserted into the structure. Disagreements were observed for the first and second run adsorption isotherms of H 2 O and NH 3, indicating that there is a strong interaction contributing to H 2 O and NH 3 adsorption. Insertion of NH 3 into the tunnels of H−Hol is a very slow process; the rate-determining step is that of insertion into the inner H + sites. H + sites on H−Hol play an important role in both NH 3 and H 2 O adsorption. Adsorption and FT-IR results demonstrate that stepwise dehydration decreases the H + sites available for NH 3 adsorption, some but not all of which are recoverable by rehydration.