Disclosed are a radiating wall catalytic reactor for providing heat from the inside wall surface 8 of a reaction chamber 1 by radiation 16 to support an overall endothermic gas phase chemical reaction taking place in the reaction chamber 1, and a process for carrying out a chemical reaction in the reactor. The reaction chamber 1 is provided with an entrance port 2 for introducing a gaseous reactant(s) in a continuous manner into the chamber 1 and an exit port 3 to enable the gaseous product(s) to leave the chamber 1 in a continuous manner. The reaction chamber 1 includes a plurality of catalyst segments (A)5, which has one void segment (B)6 on either side of it; and the reaction chamber 1 is made of a material(s) that is (are) suitable to resist a temperature of 700° C. or more.