Synthesis, characterization and thermal stability of cobalt salts of Keggin-type heteropolyacids supported on mesoporous silica

Abstract

Some heteropoly salts–mesoporous silica composites were prepared from Co salt of molybdophosphoric acid CoHPMo12O40 (CoHPM) by supporting on mesoporous silica in different concentrations (20–40 mass% CoHPM) of active phase. The structure and texture of these CoHPM/silica composites were studied by powder X-ray diffraction, Fourier transformed infra-red (FT-IR) and micro-Raman spectroscopy, nitrogen physisorption at 77 K and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM–EDS). Thermal stability was investigated by thermogravimetric analysis, differential thermal analysis and differential scanning calorimetry. FT-IR and Raman studies showed that heteropoly anions preserved their Keggin structure after impregnation on mesoporous silica support. From SEM–EDS analysis, it observed that for low loading of active phase, the average content of chemical elements (Mo, P and Co) is close to the stoichiometric values, while for higher loadings, the samples exhibit some deviation of concentration values from the stoichiometric ones. The mesoporous silica–HPA composites are thermally more stable than the parent acids, due to the strong anion-support interaction.