Reaction in the system N(CH3)4-ZrO2-P2O5-H2O. Preparation and characterization of framework zirconium phosphates (NH4)xH1-xZr2(PO4)3 and HZr2(PO4)3.

The hydrothermal reaction in the system ZrO2–P2O5–H2O in the presence of tetramethylammonium ions was examined within the temperature range 160–350 °C. This reaction resulted in the formation of framework zirconium phosphates (NH4)xH1−xZr2(PO4)3·yH2O (0.6≤x≤1,y≤0.3) as well as some other phases, including two tetramethylammonium intercalates. The framework phases were rhombohedral with lattice constants of, e.g., a=8.669 and c=24.23 A for x=1.0. These phases were deammonated at 400–640 °C and converted to the proton-exchanged form HZr2(PO4)3. The protons of this phase are easily exchanged by unhydrated Li+ and Na+ ions, but not by K+ and Cs+, owing to the sieving effect of the bottleneck in the (Zr2P3O12)−1 framework. The acid strength of the proton form is a little weaker than that of α-zirconium phosphate.