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

The sorption of gaseous ammonia into solid polyoxometalates such as the Keggin (H4SiMo12O40, H4SiW12O40 and H3PW12O40) and Dawson type (H6P2W18O62) heteropolyacids was studied. The combination of microbalance measurements and FT-IR spectroscopy confirmed the formation of diammonium ion N2H7+ 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.