The Environmentally Friendly Synthesis of Heteropolyacids.

Abstract 76 5.1 Introduction 76 5.2 Experimental 775.2.1 Synthesis of the (NH4)6P2W18 O62.13H2O and (NH4)6P2Mo18O62.12H2O Salts 775.2.2 Ion Exchange Method 77 5.2.3 Additional Materials 78 5.2.4 Characterization Techniques 785.2.4.1 Infrared Spectroscopy 78 5.2.4.2 Raman Spectroscopy 78 5.2.4.3 Thermo-Gravimetric and DifferentialThermal Analyses (TGA-DTA) 79 5.2.4.4 Nuclear Magnetic Resonance 31P NMR 79 5.2.4.5 Specific Surface Area and PoreVolume Determination 79 5.2.4.6 Chemisorption and Temperature ProgrammedSurface Reaction Spectroscopy 79 5.3 Results and Discussion 805.3.1 Operative Conditions for the Synthesis of Heteropolyacids through Ion Exchange 805.3.2 Thermal Stability of Wells-Dawson Heteropolyacids 83 5.3.3 Insights on the Acid Properties of Wells-DawsonHPAs through Molecular Probes: Comparison with Various Catalytic Materials 86 5.3.3.1 Number and Nature of the AccessibleActive Acid Sites 86 5.3.3.2 Strength of the Active Acid Sites: ActivationEnergy for Surface Species Reaction 895.4 Conclusions 91 Acknowledgments 91 References 91Fosfotungstic 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%).