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

Abstract Acidity and basicity of four hydrocalumite-type materials were studied by infrared spectroscopy through the adsorption of pivalonitrile and acetonitrile, as probe molecules. Samples were prepared by coprecipitation of the corresponding chloride salts with and without ultrasounds and later aging by refluxing under microwaves or by conventional heating. After pivalonitrile adsorption, the samples outgassed at room temperature showed very weak acidity. The number of Lewis acid sites increased after activation at 100 °C, and stronger Lewis acid sites were detected after outgassing at 400 °C. Moreover, these samples showed strong basicity due to the O 2– anions, as evidenced by the formation of (CH 2 CN) − 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 as catalyst for the transesterification of glycerol with dimethylcarbonate.