The interaction of vanadyl porphyrin with the acid sites of the HY zeolite surface is investigated. Structural changes, partial population charges and relative energies induced by the interaction between vanadyl porphyrin and the zeolite surface are estimated with recourse to the Born-Oppenheimer semiclassical molecular dynamics technique in conjunction with density functional theory. An energy optimization process indicates that bond lengths and charge populations of the acid sites are barely distorted when vanadyl porphyrin is adsorbed onto the zeolite surface. At the expense of surmounting a large energy barrier, a dynamic interaction results in the breaking of an OH bond of the surface acid site by the vanadyl porphyrin. Given the amount of energy involved in such a process, the destruction of the catalyst crystal structure by vanadyl porphyrin shows a low probability of occurrence. (C) 2009 Elsevier B.V. All rights reserved.