Characterization of surfacial basic sites of sol gel-prepared alkaline earth fluorides by means of PulseTA®

The CO2 adsorption properties of a series of different sol gel-prepared metal fluorides of the alkaline earth row and aluminium, among them two mixed (doped) metal fluorides was investigated by applying Pulse Thermal Analysis. The alkaline earth flurorides, which exhibit nanoscopic properties, have not only acid, but basic sites as well. For the first time, these basic sites have been characterized by the exothermicity of the first CO2 injection pulse. If the basicity is weak or absent, the alternating injection of water can generate OH groups at the surface of the fluorides. They mostly act as basic sites and allow a stronger differentiation of the basic properties, but the formed OH groups can exhibit an acid character as well. The impact of OH groups can affect a different influence on the sorption properties of the solids: the adsorption ability vs. CO2 can be promoted, suppressed or remain unaffected.