Assessment through FT-IR of surface acidity and basicity of hydrocalumites by nitrile adsorption

Acidity and basicity of four hydrocalumite-type materials were studied by infrared spectroscopy through theadsorption of pivalonitrile and acetonitrile, as probe molecules. Samples were prepared by coprecipitation of thecorresponding chloride salts with and without ultrasounds and later aging by refluxing under microwaves or byconventional heating. After pivalonitrile adsorption, the samples outgassed at room temperature showed veryweak acidity. The number of Lewis acid sites increased after activation at 100 °C, and stronger Lewis acid siteswere detected after outgassing at 400 °C. Moreover, these samples showed strong basicity due to the O2–anions,as evidenced by the formation of (CH2CN)−anions after acetonitrile adsorption at high temperature.Additionally, coprecipitation under ultrasounds seems to enhance the basicity of the resulting hydrocalumite.This could explain the higher activity observed for the sample synthesized under ultrasounds when tested ascatalyst for the transesterification of glycerol with dimethylcarbonate