A tool for direct quantitative measurement of surface Brønsted acid sites of solids by H/D exchange using D2O Original Research Article

A tool for direct and quantitative determination of surface Brønsted acidity of solids in terms of number, type and force based on quantitative H/D exchange kinetic between gaseous D2O and the acid solid, i.e. the hydron of the –O–H acid surface groups, has been developed. This method has been applied to materials covering the whole range of acidity, from very low acidic materials (e.g. carbonaceous solids) to high acidic materials (e.g. acidic oxides or zeolites). Calibration was performed using well-characterized zeolites with known acidities and allowed the number of surface Brønsted acid sites (in μmol/g) to be determined using the integrated surfaces of the H/D experimental exchange curve given by the direct measurement of the exchanged HDO molecule signal by mass spectrometry. The determination of the force of the acidity was directly linked to the rate constant of the first step of the H/D exchange. This method allows, after deconvolution of the H/D experimental curve, the number and force of each type of surface Brønsted acid sites to be determined.