The "n-hexane and steam" gaseous mixture was first sent through a precatalytic zone containing quartz beads (temperature Tt), and then through a catalyst bed (T-2). The latter contained a ZSM5 zeolite or a zeolite-containing hybrid catalyst. By moderately increasing TI (T-2 being kept constant), significant increases in the total n-hexane conversion and in the total yield of light olefins were obtained. The ethylene/propylene product ratio could be varied widely, for instance, from 1.0 to 2.0 by varying T-1 from 660 to 720 degreesC. Such temperature effect of zone I on the overall process performance was explained by the formation of selectivity modifiers such as diolefins. With the hybrid catalyst, the enhanced production of light olefins was also assigned to the formation of large olefins on the Cr-Al-containing cocatalyst.