Thermal stability of polyoxometalate compound of Keggin K8[2-SiW11O39]∙nH2O supported with SiO2

Abstract

Synthesis through sol-gel method and characterization of polyoxometalate compound of K₈[b₂-SiW₁₁O₃₉]∙nH₂O supported with SiO₂ have been done. The functional groups of polyoxometalate compound  was characterized by FT-IR spectrophotometer for the fungtional groups and the degree’s of crystalinity  using XRD. The acidity of K₈[b₂-SiW₁₁O₃₉]∙nH₂O/SiO₂ was determined qualitative analysis using ammonia and pyridine adsorption and the quantitative analysis using potentiometric titration method. The results of FT-IR spectrum of K₈[b₂-SiW₁₁O₃₉]∙nH₂O appeared at  wavenumber 987.55 cm^-1 (W=O), 864.11 cm^-1 (W-Oe-W), 756.1 cm^-1 (W-Oc-W), 3425.58 cm^-1 (O-H), respectively and spectrum of  K₈[b₂-SiW₁₁O₃₉]SiO₂ appeared at wavenumber  956.69 cm^-1 (W=O), 864.11 cm^-1 (W-Oe-W), 3448.72 cm^-1 (O-H), respectively. The diffraction of XRD pattern of K₈[b₂-SiW₁₁O₃₉]∙nH₂O and K₈[b₂-SiW₁₁O₃₉]∙nH₂O/SiO₂ compounds show high crystalinity. The acidic properties showed K₈[b₂-SiW₁₁O₃₉]∙nH₂O/SiO₂ more acidic compared to K₈[b₂-The SiW₁₁O₃₉]∙nH₂O. The qualitative analysis showed pyridine compound adsorbed more of polyoxometalate compound of K₈[b₂-SiW₁₁O₃₉]∙nH₂O/SiO₂. Analysis of stability showed that the K₈[b₂-SiW₁₁O₃₉]∙nH₂O/SiO₂ at temperature 500°C has structural changes compare to 200-400^oC which was indicated from vibration at wavenumber 800-1000 cm^-1.

Keywords : K₈[b₂-SiW₁₁O₃₉]∙nH₂O, polyoxometalate, SiO₂.