FT-IR and microbalance studies of diammonium ions formation in heteropolyacids

Abstract

The sorption of gaseous ammonia into solid polyoxometalates such as the Keggin (H 4SiMo 12O 40, H 4SiW 12O 40 and H 3PW 12O 40) and Dawson type (H 6P 2W 18O 62) heteropolyacids was studied. The combination of microbalance measurements and FT-IR spectroscopy confirmed the formation of diammonium ion N 2H 7 + in the bulk of heteropolyacids of both types, which was found to depend on both the ammonia equilibrium pressure and sorption temperature. The diffusion coefficients of the ammonia molecules penetrating into the bulk of heteropolyacids were calculated.