The existence and thermal etability of H2O in 12-molybdophosphoric acid (PMA) have been studies by temperature programmed desorption-mass spectrographic (TPD MS) and infrared spectrography (IR). A PMA sample containing 19.1 H2O/P, H3(PMo19O10)center dot 17.6 H2O, was prepared, its water content was determined according to Fig.1. The TPD MS spectrum of H2O (m/z = 18) in PMA (solid line Fig.3) was recorded after vaccum outgassing(0.27Pa) at 290K (the total time of outgassing in the range 77.4-290K was 142.5 min). Separated spectra (Fig.3) and their parameters simulated by spectrogram superposition method([1]) and consulting table method([2]) (Table1) show that there exist 7 kinds of H2O in PMA. In situ IR spectra for PMA at different conditions (Fig.4) revealed that the ruptures of various oxygen bonds proceeded simultaneously at 603K (Table 2). Integration of the total area of the upper temperature peaks 5-7 yielded the n value of 1.51 for water molecules desorbed per PMA unit (H2O?P), which consists with 1.5 for the protonic water. These results lead us to conclude, firstly, that the peak 1 is assigned to the water in the secondary structure of PMA, this water is quite easy to be outgassed at 290 K and its main part had been evacuated before TPD. Secondly, peaks 2-4 with modium binding energies are assigned to three kinds of water in the hydronium ions which are hydrogen-bonded to bridge oxygen O(sic), verminal oxygen O(sic) or phosphor oxygen O(sic) in the primary Keggin structures. Thirdly, peaks 5-7 with strong binding energies are assigned to another three kinds of water formed from protons with O(sic), O(sic) or O(sic). Accompaning with desorption of the three kinds of protonic water, the Kesgic structure is gradually destroyed till entirely collapsed at last.
