Identification of solid solutions and other phases in strontium and barium catalysts containing oxides of magnesium, aluminum or silicon as additive: II. catalyst characterisation

Abstract

This paper presents the results of thermoanalytical studies (TG/DTA) to examine the influence of additives (MgO, Al 2O 3 or SiO 2) on the thermal stability of SrCO 3 and BaCO 3. Since any destabilization is expected to be maximised when the carbonates and the additives are in intimate contact, viz., solid solution, the possibility of the formation of solid solution and other stoichiometric compounds has been explored and the phases identified by X-ray diffraction (XRD). Thermogravimetry data show that the incorporation of MgO in SrCO 3 and BaCO 3 lowers the carbonate decomposition temperatures by as much as about 150°C. Destabilization is also observed using alumina or silica, although the extent to which this occurs is moderate compared with MgO as an additive. Moreover, SiO 2 interacts strongly and irreversibly forming Ba 2SiO 4, BaSiO 3 or Sr 2SiO 4 and SrSiO 3. Al 2O 3 also interacts, albeit mildly, forming BaAl 2O 4 or SrAl 2O 4. A solid solution of the type (MgBa) (CO 3) 2 is the only phase detected by XRD in the coprecipitated carbonates containing magnesium. Carbonate stability depends on the environment. Whilst a carbon dioxide environment suppresses decomposition, hydrogen enhances decomposition through provision of another reaction channel.