Incorporation of gallium and iron into MCM-41-type silicas leads to creation of active and selective catalysts for the dehydro-enation of hydrocarbons. This catalysts demonstrate remarkable stability with time on stream and do not suffer from repeated reaction-reoxidation cycles. Ga-MCM-41 is particularly efficient for the dehydrogenation of light alkanes. At 550degreesC isobutane is converted into a mixture of C-2-C-4 olefins containing 52% of isobutene, which corresponds to 32% of the equilibrium conversion into isobutene at this temperature. Fe-MCM-41 shows the best performance for ethylbenzene dehydrogenation into styrene, in particular, at 600degreesC, the yield over this catalyst is 38% per pass and selectivity is 82%, which corresponds to 64% of the equilibrium value. The catalysts have been characterised by XRD, volumetry, infrared spectroscopy, ammonia temperature-programmed desorption (TPD) and temperature-programmed reduction (TPR). Catalytic activity is associated with the presence of nanoparticles of oxides, entrapped in the pores or embedded in the silica network, which generate reducible species able to split C-H bonds and allow fast recombinative desorption of hydrogen and olefins. (C) 2003 Elsevier B.V. All rights reserved.