Kinetics study of the isomerization of xylene on ZSM-5 zeolites: the effect of the modification with MgO and CaO Original Research Article

Xylene isomerization over HZSM-5, MgO-HZSM-5, and CaO-HZSM-5 zeolites has been studied using the pulse microreactor-chromatograph technique and the dynamic modeling method. The rate constants, activation energies, and activation entropies for each step in the reaction network on the catalysts have been obtained. These results indicate that strong acidity can favour the conversion of m-ando-xylene, while the isomerization of p-xylene not only takes place on strong acidic sites, but also on the weaker acidic sites. The parameters also indicate that under a loading amount of MgO or CaO in a mole ratio to framework aluminum equal to 1:1, the influence of steric encumbrance caused by the introduction of MgO or CaO is less as compared with the changes of the surface acidity.