Adsorption and catalytic properties of MCM-22: The influence of zeolite structure

A combination of infrared spectroscopy and adsorption and microcalorimetric studies of molecules with different kinetic diameters, such as toluene, meta- and orthoxylene, and 1,2,4-trimethylbenzene, together with consecutive adsorption of these molecules, confirms the presence in MCM-22 of 10-membered ring channels and cavities of larger dimensions, both of which can be reached from the external surface. From the kinetic diameters of the adsorbates the dimension of the two types of void species has been estimated. The implications of pore topology on catalysis have been discussed on the basis of selectivity results obtained during alkylation of toluene by methanol and ethanol. The presence of the two types of unconnected cavities determines the ratios of para- to ortho isomers as well as the ratio of mono- to dialkylates.