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-prog rammed desorption with mass spectrometry detection (TPD-MS) and of Fourier transform infra-red (FTIR) analysis of adsorbed pyridine, in order to compa re the surface concentration of acid sites potentially involved in a specif ic catalytic process, as determined through the two techniques. Up to three distributions of acid sites were evidenced in the investigated catalysts b y deconvolution of the TPD-MS spectra recorded after pyridine adsorption at different temperatures (150-300 degrees C), depending on the type of catal yst and on its dealumination degree. FTIR analysis showed that pyridine ads orption on acid solids occurs under kinetic control and that equilibrium at tainment implies a redistribution of pyridine molecules between Bronsted an d Lewis surface sites. The reliability of the two titration techniques was verified by the good match between the values of overall surface acidity de termined through them under equilibrium conditions at 150 degrees C. (C) 19 99 Elsevier Science B.V. All rights reserved.