Alkylation of benzene with propene has been investigated on a series of H-Beta zeolites with different Si/Al ratio: 10, 35 and 66, using different techniques such as FTIR, C-13 NMR and catalytic testing. It has been shown that H-Beta zeolite (Si/Al ratio = 10) is a very active catalyst for this reaction with propene, but if leads also to fast oligomerization even at lower reaction temperatures. C-13 NMR experiments have demonstrated for the first time that the reaction of alkylation is already complete at -80 degrees C on these catalysts. Dealuminated H-Beta zeolites are less active but lead to less aromatic by-products (especially n-propylbenzene) and the deactivation due to the coke formation is reduced. The high ratio of benzene/propene favors the formation of cumene and suppresses the oligomerization of propene. Triisopropylbenzene (TIPB) can also be formed at low temperatures ( < 100 degrees C) and then is transformed by transalkylation into diisopropylbenzene (DIPB) at higher temperatures (> 130 degrees C). The present work reveals that the alkylation of benzene by propene occurs via an Eley-Rideal type mechanism. The apparent activation energy for this reaction has been determined and shows to decrease as the Si/Al ratio of H-Beta zeolites increases. The relatively low apparent activation energies obtained for this reaction on a series of H-Beta zeolites studied suggests that it exists a diffusion step of reactants and products between the silanols of the Beta zeolite.