The involvement of hydrogen back-spillover is confirmed for the aromatization of ethylene. Using hydrogen monitoring during catalytic reactions with ethylene, it has been observed that the amount of hydrogen in the gaseous effluents is much more important on hybrid catalysts than on pure ZSM-5 zeolites. The active sites on ZnO based co-catalysts are believed to be partial reduction zinc sites created during the induction period. ZnO precipitate favors the release of hydrogen species as ethane. ZnO/Al2O3 co-precipitate favors hydrogen recombination.