Thermodynamic and Spectroscopic Analyses of Zirconium Phosphate-Absorbed Ammonia

Zirconium phosphate is insoluble in water and has a large ammonia storage capacity with a low ammonia plateau concentration in water. In this study, the thermodynamics of ammonia on zirconium phosphate (ZrP) and the local structure such as the interaction between ammonia and ZrP have been investigated using the temperature dependence of ammonia concentration composition isotherm (CCI) measurements, 31P magic angle spinning nuclear magnetic resonance (31P MAS NMR), and Fourier transform infrared (FT-IR) spectroscopy. The standard enthalpy changes ΔH 0 of ZrP-absorbed ammonia (1 mol­(NH3) mol–1 (ZrP):ZrP-NH3 and 2 mol­(NH3) mol–1 (ZrP):ZrP-2NH3) were calculated to be ≤ −111 and −64 kJ mol−1(NH3), respectively. 31P MAS NMR and FT-IR indicated that the local structures of ZrP-NH3 and ZrP-2NH3 were different. It was suggested that nitrogen in ammonia reacts with hydrogen in the phosphate group to form a N–H covalent bond in NH4 + having hydrogen bonds, although the number of hydrogen bonds in ZrP-NH3 was smaller than that in ZrP-2NH3.