SORPTION AND SORPTION KINETICS OF PYRIDINE IN H-ZSM-5 AND H-MORDENITE

Time-resolved FTIR techniques are used to investigate the sorption and sorption kinetics of pyridine upon uptake into zeolite structures. The strength of acidic Bronsted sites and Lewis centres in hydrogen mordenite and hydrogen ZSM-5 are compared. From the measurements, diffusion coefficients are derived. The zeolite samples used possess both types of sites. At a sorption temperature of 395-475 K, in H-MOR the Lewis sites are saturated at partial pressures of pyridine as low as 11.5 Pa, whereas the Bronsted sites show an increasing population with increasing partial pressures up to p(Py) > 1000 Pa. The opposite is true for H-ZSM-5. For H-MOR MOR the diffusion coefficients, which are significantly dependent on the coverage, range at 475 K from 10(-12) to 10(-11) cm(2).s(-1) whereas those for H-ZSM-5 are greater by one order of magnitude.