UPThèses

MCM-22 has a very peculiar pore structure with three independent pore systems: narrow sinusoidal channels (4.1×5.1 Å), large supercages (ø 7.1 Å, height 18.2 Å) accessible through (4.0×5.5 Å) openings and external cups (ø 7.1 Å, depth 7.0 Å). The aim of this thesis was to study the global catalytic properties and ascertain the catalytic role of each pore system of HMCM-22 zeolite (Si/Al=14.5) on methylcyclohexane and n-heptane transformations at 350ºC. To this end, the participation of each pore system was established by selectively deactivating the supercages through coke deposition and poisoning the external cups acid sites. Supercages play the major catalytic role on both reactions. Sinusoidal channels present a very low activity due to high steric constraints. External cups acid sites are more active than those of supercages in methylcyclohexane transformation due to the absence of diffusion limitations. The results revealed that the external cups acid sites are not able to catalyze n-heptane reaction, which is ascribed to a lower acid strength and/or to the absence of confinement effect in the external cups. Adsorption of different molecules allowed the determination of the micropore volume of each pore system. An intermediate behavior of HMCM-22 between USHY (large pores) and HZSM-5 (intermediate pores) zeolites was observed on both reactions. The activities per acid site of HMCM-22 zeolite were closer to those of HZSM-5. Dealumination by acid leaching of the HMCM-22 zeolite removed mainly the acid sites located on the supercages and external cups, whereas those of the sinusoidal channels were almost not affected