Comparison between the surface acidity of solid catalysts determined by TPD and FTIR analysis of pre-adsorbed pyridine

A series of both crystalline (Y zeolites, beta zeolites and mordenites) and amorphous alumino-silicates were investigated by means of temperature-programmed desorption with mass spectrometry detection (TPD-MS) and of Fourier transform infra-red (FTIR) analysis of adsorbed pyridine, in order to compare the surface concentration of acid sites potentially involved in a specific catalytic process, as determined through the two techniques. Up to three distributions of acid sites were evidenced in the investigated catalysts by deconvolution of the TPD-MS spectra recorded after pyridine adsorption at different temperatures (150-300 degrees C), depending on the type of catalyst and on its dealumination degree. FTIR analysis showed that pyridine adsorption on acid solids occurs under kinetic control and that equilibrium attainment implies a redistribution of pyridine molecules between Bronsted and Lewis surface sites. The reliability of the two titration techniques was verified by the good match between the values of overall surface acidity determined through them under equilibrium conditions at 150 degrees C. (C) 1999 Elsevier Science B.V. All rights reserved.