Minimalistic Synthesis of α-Zirconium Diammonium Phosphate and Zirconia for Applications in Ion Exchange and Catalysis

Abstract

α-Zirconium diammonium phosphate (α-Zr(NH4PO4)2·H2O) and ZrO2 find useful applications as ion-exchangers and catalysts. The current syntheses of these compounds are usually via solution-precipitation methods that require solvents and excess of reagents. An essentially solvent-free approach with only the water of crystallization for homogenization has now been developed, by which α-zirconium diammonium phosphate and ZrO2 can be synthesized with minimalistic ratios of reactants. α-Zr(NH4PO4)2·H2O was directly accessible in a single step, in contrast to the currently used two-step solution processes. Highly crystalline α-Zr(NH4PO4)2·H2O was obtained from a reaction composition of ZrOCl2·8H2O:4(NH4)2HPO4:0.05NaF after heating at 120 °C for 1 day. α-Zr(NH4PO4)2·H2O showed excellent sorption for Pb2+ and Cu2+ with removal efficiencies ≥99% and high distribution coefficients of 106–107. Similarly, by this minimalistic approach, different modifications of ZrO2 were obtained depending on the base and temperature. Monoclinic ZrO2 formed at 160 °C from stoichiometric mixtures of ZrOCl2·8H2O and ammonium carbonate or with 1.5 times excess urea. Tetragonal ZrO2 was obtained with a stoichiometric amount of NaOH. The monoclinic ZrO2 showed higher activity than the tetragonal form in the Meerwein–Ponndorf–Verley reduction of furfural to furfuryl alcohol.