Influence of carbonaceous deposits on the acidity of a zeolite with two non-interconnected pore systems: MCM-22

Abstract

H-MCM-22 zeolite samples used in n-heptane cracking at 450 °C for time-on-stream between 2 min and 100 h, hence with different coke contents (from 0.45 to 6.9 wt%), were characterized by FTIR spectroscopy before and after pyridine adsorption. As is observed with the zeolites with only one pore system, coke molecules interact preferentially with the most acidic hydroxyl groups, which is confirmed by the large decrease in the number of the protonic sites able to retain pyridine adsorbed at high temperature. A decrease in the number and strength of the Lewis acid sites able to retain pyridine adsorbed is also observed above 0.5 wt% coke, which can be related to blockage by coke of the access of pyridine molecules to the supercage pore system.