The effects of dealumination of BEA zeolite on the formation of nickel active sites and the performance of Ni-containing BEA zeolite catalysts in the steam reforming of ethanol have been studied. Ni-containing BEA zeolite catalysts were prepared by the impregnation of unmodified and dealuminated BEA zeolites with Ni(NO3)(2) precursor. The properties of Ni(10)HAlBEA and Ni(10)SiBEA zeolite catalysts were studied by means of X-ray diffraction, H-1, Al-27 and Si-29 magic-angle spinning nuclear magnetic resonance, Fourier-transform infrared and Raman spectroscopy, transmission electron microscopy, temperature-programmed reduction, temperature-programmed ammonia and hydrogen desorption methods. High initial activity and selectivity of Ni(10)HAlBEA to hydrogen and carbon dioxide with unmodified BEA zeolite support in the steam reforming of ethanol reaction performed at 500 degrees C was observed. However, fast deactivation of Ni(10)HAlBEA catalyst, manifested in the decrease of water conversion, drop of selectivity to H-2 and CO2, and increase in the selectivity to ethylene with the time-on-stream, was observed. In contrast, Ni(10)SiBEA zeolite catalyst showed lower initial activity but higher durability and resistance for carbon deposition. It was stated that dealumination of BEA zeolite led to the slight structural changes and simultaneously pronounced decrease of acidity. Formation of the large nickel crystallites was hindered on Ni(10)SiBEA zeolite catalyst. TEM and Raman spectroscopy studies indicated that deactivation of Ni(10)HAlBEA was related to formation of nickel mediated filamentous, graphitic and amorphous carbon deposits. Much smaller amounts of filamentous carbons were observed on the Ni(10)SiBEA zeolite catalyst prepared by the use of dealuminated zeolite support.