chapter  5
18 Pages

The Environmentally Friendly Synthesis of Heteropolyacids

WithGraciela M. Valle, Silvana R. Matkovic, Luis A. Gambaro, Laura E. Briand

Abstract .................................................................................................................... 76 5.1 Introduction .................................................................................................... 76 5.2 Experimental .................................................................................................. 77

5.2.1 Synthesis of the (NH4)6P2W18 O62.13H2O and (NH4)6P2Mo18O62.12H2O Salts ........................................................... 77

5.2.2 Ion Exchange Method........................................................................ 77 5.2.3 Additional Materials .......................................................................... 78 5.2.4 Characterization Techniques .............................................................. 78

5.2.4.1 Infrared Spectroscopy......................................................... 78 5.2.4.2 Raman Spectroscopy .......................................................... 78 5.2.4.3 Thermo-Gravimetric and Differential

Thermal Analyses (TGA-DTA) ......................................... 79 5.2.4.4 Nuclear Magnetic Resonance 31P NMR............................. 79 5.2.4.5 Specific Surface Area and Pore

Volume Determination........................................................ 79 5.2.4.6 Chemisorption and Temperature Programmed

Surface Reaction Spectroscopy.......................................... 79 5.3 Results and Discussion .................................................................................. 80

5.3.1 Operative Conditions for the Synthesis of Heteropolyacids through Ion Exchange ............................................ 80

5.3.2 Thermal Stability of Wells-Dawson Heteropolyacids....................... 83 5.3.3 Insights on the Acid Properties of Wells-Dawson

HPAs through Molecular Probes: Comparison with Various Catalytic Materials................................................................ 86 5.3.3.1 Number and Nature of the Accessible

Active Acid Sites................................................................ 86 5.3.3.2 Strength of the Active Acid Sites: Activation

Energy for Surface Species Reaction................................. 89

5.4 Conclusions .................................................................................................... 91 Acknowledgments.................................................................................................... 91 References................................................................................................................ 91

Fosfotungstic and fosfomolybdic Wells-Dawson heteropolyacids, H6P2W18O62.xH2O and H6P2Mo18O62.xH2O, respectively, were synthesized through ion exchange with a higher yield (~90%) than the conventional organic route (~70%).