ABSTRACT
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%).
