Characterization of the structural and surface properties of a synthesizedhydrous hollandite by gaseous molecular adsorption

The structural and surface properties of a hydrous hollandite-type manganes e oxide (H-Hol) were examined by adsorption using different gases with mole cular diameters below 0.4 nm. N-2, O-2, Ar, CO, and CO2 with diameters abov e 0.33 nm are excluded from the tunnel structure of H-Hol, whereas H2O and NH3 with diameters below 0.265 nm can be inserted into the structure. Disag reements were observed for the first and second run adsorption isotherms of H2O and NH3, indicating that there is a strong interaction contributing to H2O and NH3 adsorption. Insertion of NH3 into the tunnels of H-Hol is a ve ry slow process; the rate-determining step is that of insertion into the in ner H+ sites. H+ sites on H-Hol play an important role in both NH3 and H2O adsorption. Adsorption and FT-IR results demonstrate that stepwise dehydrat ion decreases the H+ sites available for NH3 adsorption, some but not all o f which are recoverable by rehydration.