The transformation of methylcyclohexane at 723 K over on a USHY sample and on an FCC catalyst composed of 30% USHY and 70% matrix containing 25% Al2O3 was studied. With both samples, C2-C7 alkenes and alkanes, cyclopentane and methylcyclopentane (cracking products), dimethylcyclopentanes and ethylcyclopentane (isomers) and aromatics appeared as primary products. The activity and selectivity of fresh samples as well as the influence of coke deposits on porosity and selectivity are discussed.

After steaming at 530° C for 30 minutes and for 6 hours, a Ga/HZSM5 catalyst was characterized by three model reactions (meta-xylene isomerization, propane aromatization and methylcyclohexane transformation). The activity and selectivity of this catalyst were compared to those of a fresh Ga/HZSM5 catalyst. It was demonstrated that hydrothermal treatment provokes a significant decrease in the dehydrogenation activity of the gallium species and a small decrease in the protonic acidity of the catalyst.

The presence of gallium on HZMS5 zeolites increases the rate of coke elimination in their regeneration in hydrogen. The gallium species should contribute to the hydrogenation of the coke molecules and the acid sites should favour their crackings. However, the location of the coke molecules (near the outer surface and near the gallium species) instead of their nature seems to be the determining parameter for their elimination

HZSM5 zeolite was modified by exchanging proton by niobium (V). Several samples were obtained with various degrees of exchange. Pore volumes and acidity were measured to characterize these exchanged zeolites. Catalytic properties were evaluated with two reaction tests: m-xylene transformation and n-heptane cracking. The introduction of niobium on HZSM5 zeolite decreases the diffusion coefficient of 2-methyl-pentane and increases the zeolite acidity. The sample containing niobium are initially more active in cracking of n-heptane and m-xylene isomerization than HZSM5 alone.