Sorption Properties of AlPO4-5 and SAPO-5 Zeolite-like Materials

We have studied by volumetric adsorption isotherm measurements the sorption properties of different AlPO 4 -5 or SAPO-5 samples, for sorbate species characterized by a large range of molecular size: D 2, Kr, Ar, C 2 D 2, CO 2, CH 4, CF 4, and C(CH 3 ) 4 . The highest sorption capacities, Q max, greatly depend on the sorbate molecular size. A difference of 1 order of magnitude is observed between hydrogen and neopentane. In addition, we have found that the sorption capacities of the four analyzed AlPO 4 -5 or SAPO-5 samples vary by almost a factor of 2. This result clearly shows that, as a consequence of the one-dimensional character of the AFI micropore network, Q max is very sensitive to small amounts of crystalline defects or impurities. For methane, Q max is equal to 6 mol/uc, a quantity that is not compatible with the commonly accepted value of the internal diameter of the AlPO 4 -5 micropore diameter, ⌀ M = 7.3 Å. Moreover, an interesting phase transition phenomenon has been observed during the sorption of krypton and methane, a result that can be the consequence of the good parametric agreement between such sorbate species and the AlPO 4 -5 inner surface.