Preparation and properties of the heteropolyoxometalates of large organic cation with molybdotungstosilicic acids

Abstract

Some new heteropolyoxometalates of large organic cations with molybdotungstosilicic acids (general formula: (CTMA) 4 SiMo x W 12-x O 40 •mH 2 O•nDMF, x=0,2,4,6,8,10,12) were prepared by the reaction of cetyltrimethylammonium bromide (CTMAB,C 16 H 33 N(CH 3 ) 3 Br) with H 4 SiMo x W 12-x O 40 (x=0,2,4,6,8,10,12) in aqueous solution and recrystallization in DMF, and characterized by elemental analysis, IR spectra,TG-DTA and XRD techniques. The IR spectrum confi rms the presence of Keggin structure and organic cations in these compounds, and it is indicated that the stretching vibration of the M-Od, M-Ob-M and Si-Oa becomes more red-shifted when molybdenum is gradually substituted for the tungsten atom. In particular, the thermal decomposition of the heteropolyoxometalates was studied in nitrogen atmosphere. The TG-DTA curves show that their thermal behaviors not only contain the release of water molecule, DMF molecule, CTMA and its fragments but also contains simultaneous collapse of Keggin anion. Their end products of the thermal decomposition are the mixture of WO 3 , MoO 3 and SiO 2 . And from the final decomposition temperature of view, it is found that the thermal stability of these compounds gradually is decreased when the number of molybdenum atoms is increased.

Polyoxometalate/Ionic Liquid Desulfurization System for Hydrogen Sulfide Removal from High-Temperature Gas Stream

“…Figure 1 b is the XRD pattern of (n-Bu 4 N) 3 VMo 12 O 40 . The diffraction peaks at 11.7°, 15.6°, 23.8°, and 31.7° are the characteristic peaks of Keggin polyoxometalates [ 19 , 20 , 21 ]. The FT-IR and XRD spectra revealed that (n-Bu 4 N) 3 VMo 12 O 40 was successfully synthesized.…”