Thermal Stability and Acidity of Silica Supported Keggin Type Polyoxometalate K4[-SiW12O40]•nH2O

Abstract

Silica supported polyoxometalate K₄[a-SiW₁₂O₄₀]·nH₂O was prepared systematically using tetraethyl ortho silicate by sol gel method to form K₄[a-SiW₁₂O₄₀]·nH₂O/Si. Compound K₄[a-SiW₁₂O₄₀]·nH₂O/Si was characterized by diffraction, spectroscopic, and acidity  analyses follow by thermal activity test at higher temperature up to 600 ^oC. Analysis of FTIR spectrum showed all unique vibration of polyoxometalate K₄[a-SiW₁₂O₄₀]·nH₂O was appeared at wavenumber 800-1000 cm^-1 before and after supporting process. Crystallinity of K₄[a-SiW₁₂O₄₀]·nH₂O and K₄[a-SiW₁₂O₄₀]·nH₂O/Si were also similar without changing Keggin structure. Compound K₄[a-SiW₁₂O₄₀]·nH₂O/Si showed higher acidity than K₄[a-SiW₁₂O₄₀]·nH₂O probably due to Lewis acidity species. Keggin structure of K₄[a-SiW₁₂O₄₀]·nH₂O/Si was still retained up to 600 ^oC showing thermal stability of K₄[a-SiW₁₂O₄₀]·nH₂O/Si at high temperature.

Keyword : Keggin polyoxometalate, tetraethyl ortho silicate, thermal stability, acidity