A device for burning a fuel/oxidant mixture in a strongly exothermic reaction, consists of a reactor with a combustion chamber containing at least one first porous material and at least one second porous material in separate zones A and C. The zones are designed in such a way that an exothermic reaction can only occur in zone B, and with one or more feed lines for the fuel and for the oxidant, whereby zone A, which consists of the first porous material, is separated by a distance of approximately 10 mm to 4000 mm, for example approximately 20 mm to 500 mm, equating to one zone B, from zone C which consists of the second porous material and is located before zone C in a flow direction of the fuel/oxidant mixture.