H/D exchange using D2O on carbon materials: A flexible tool for surface Brønsted acidity direct measurement

A tool for direct determination of surface Brønsted acidities of solids, in terms of concentration and strength, was proposed and applied to carbon materials, based on the quantitative H/D exchange kinetics between D2O and the acid solid, i.e. the OH acid surface groups in the case of carbons. Calibration was performed using well-characterized zeolites with known acidities, and allowed the concentration of surface Brønsted acidity sites in μmol/g to be derived from the integrated surfaces of the H/D exchange curve. This was done y the direct measurement of the OHD signal via mass spectrometry. The strength of the acidity was directly linked to the rate constant of the H/D exchange kinetic. This easy of use direct method is highly flexible and covers the whole acidity scale from weakly acidic to strongly acidic materials.