The present invention relates to a process for conducting endothermic gas phase or gas-solid reactions, wherein the endothermic reaction is conducted in a production phase in a first reactor zone, the production zone, which is at least partly filled with solid particles, where the solid particles are in the form of a fixed bed, of a moving bed and in sections/or in the form of a fluidized bed, and the product-containing gas stream is drawn off from the production zone in the region of the highest temperature level plus/minus 200 K and the product-containing gas stream is guided through a second reactor zone, the heat recycling zone, which at least partly comprises a fixed bed, where the heat from the product-containing gas stream is stored in the fixed bed, and, in the subsequent purge step, a purge gas is guided through the production zone and the heat recycling zone in the same flow direction, and, in a heating zone disposed between the production zone and the heat recycling zone, the heat required for the endothermic reaction is introduced into the product-containing gas stream and into the purge stream or into the purge stream, and then, in a regeneration phase, a gas is passed through the two reactor zones in the reverse flow direction and the production zone is heated up; the present invention further relates to a structured reactor comprising three zones, a production zone containing solid particles, a heating zone and a heat recycling zone containing a fixed bed, wherein the solid particles and the fixed bed consist of different materials.