The activation and reaction zone in a gas phase hydrogen spillover experiment were separated by a fi it as in [1]. In the activation zone hydrogen was activated by a Pt/Al2O3 catalyst, the activated hydrogen reacted in the reaction zone with hexene-1, leading to a strong increase in conversion. A fur ther increase was caused by addition of oxygen into the reaction zone without contact with the catalyst, which may be interpreted as the effect of branched radical chains or an activation of the glass surface. Water does not alter the reaction. NO, a radical capturing substance, lowers the reaction rate, while N-2 shows no effect, an indication that the activation is not caused by vibrationally excited hydrogen, which should be effected similarly by NO and N-2.