IR STUDY OF H2O ADSORBED ON H-ZSM-5

Adsorption of H2O on H-ZSM-5 was studied by FT-IR in the presence of g aseous H2O in the temperature range between 293 and 423 K. Conversion of monomeric hydrogen-bonded H2O to dimeric species was clearly observ ed in IR spectra measured at 373 K by increasing the equilibrium press ure of H2O. Polymeric water was also formed by further increase of H2O pressure at the expenses of dimeric species. The frequencies and the relative intensities of IR bands due to dimeric species agree with the quantum-chemical results for H5O2+ species.