This work addresses the potential effects of steaming in the case of dealumination of Y zeolites. With this end, the interaction between 1,2,4-trimethylbenzene (1,2,4-TMB) and ultrastable Y zeolite (USY) is analyzed. The zeolite is modeled using the complete exposed USY structure of one unit cell constituted by eight socialite cages, 16 hexagonal prisms bridging the socialite cages and the formed supercage. The MM2 method is considered to evaluate the steric energies in a model of the window including the six surrounding complete sodalite cages. The Parametrized Model revision 3 (PM3) method is also used to analyze the changes in enthalpy upon 1,2,4-TMB adsorption and reaction on each cage. Finally, several calculations on the adsorption of the 1,2,4-TMB on different socialite cages are effected using the Extended Huckel method and this to complete the description about the interactions between the crystalline USY and 1,2,4-TMB molecules. Calculation results reported in this work support the high probability of carbocation formation and overall reaction in fragments removed from the zeolite. This partially destroyed zeolite display some relaxation of the original structure and allows extra accessibility of TMB to the acidic sites. (C) 2004 Elsevier B.V. All rights reserved.