Characterisation by adsorption of various organic vapours of the porosity of fresh and coked H-MCM-22 zeolites

Abstract

The microporosity of H-MCM-22 samples, fresh and deactivated by coke during methylcyclohexane transformation at 350 °C for 10 h, was characterised by adsorption of nitrogen and organic molecules of different size, namely, p- and o-xylenes, mesitylene and methylcyclohexane. Nitrogen adsorption was also carried out on the fresh sample after pre-adsorption of the hydrocarbons. All of these can fit the outer 12 MR cups, but show differences in their ability to enter the internal microporosity. p-Xylene can enter all the inner micropores, methylcyclohexane adsorbs in the supercages and at some sinusoidal channel entrances, o-xylene is adsorbed at the pore windows of the supercages only, and mesitylene is completely excluded from the inner micropores. It was deduced that the microporosity of the MCM-22 sample investigated consists of 0.01 cm 3 g −1 of outer pockets (∼5% of the total volume), 0.06 cm 3 g −1 of sinusoidal channels (∼32%) and 0.12 cm 3 g −1 of supercages (∼63%). Coke deposited during methylcyclohexane transformation caused the complete blockage of the supercages but had no effect on the outer cups and sinusoidal channels.