CHARACTERIZATION AND GAS-ADSORPTION PROPERTIES OF ALUMINUM METHYLPHOSPHONATES WITH ORGANICALLY LINED UNIDIMENSIONAL CHANNELS

Microporous aluminum methylphosphonates, AlMepO-alpha and -beta, prepa red by different procedures, were characterized mainly using Al-27, (3 1)p, and C-13 MAS NMR, TG-DTA, and IR, The MAS MMR spectra were consis tent with the crystal structures determined by the single-crystal X-ra y structural analysis published previously. All the P-31 NMR signals w ere reasonably assigned using an assumed correlation between P-31 chem ical shift and the mean Al-O-P angle around the phosphorus sites. Nitr ogen adsorption isotherms of AlMepO-beta degassed at elevated temperat ures were of type I, while those of AlMepO-alpha gave two plateaus in the low relative pressure region, The stepwise adsorption was explaine d by a packing change of the adsorbate on adsorption. The pore diamete r calculated from the maximum nitrogen adsorption capacity was consist ent with adsorption of 2,2-dimethylpropane but was larger than the siz e expected from the crystal structure of both the compounds, The water vapor isotherm was type II in the low relative pressure region, confi rming the hydrophobic nature for both compounds, AlMepO-alpha indicate d no apparent adsorption of water into the channel, but AlMepO-beta sh owed a sudden adsorption of water at P/P-0 approximate to 0.7. The dif ference in the water vapor isotherms between the compounds was explain ed based on the relationship of the size of the water clusters formed and the shape of the adsorbent channel.