Reactor (1) for formation and for catalytic conversion of a gaseous reactant mixture, wherein the reactor (1) has a reaction zone (12) and is set up to mix at least one first gas or gas mixture and one second gas or gas mixture to give the reactant mixture and supply it to the reaction zone (12), characterized in that the reactor (1) is set up to form the reactant mixture at least temporarily as an ignitable gas mixture, and in that the reactor (1) comprises a mixing chamber (11) having a boundary wall (13) provided with a number of passages (131), wherein the passages (131) are at least partially formed as nozzles having Venturi or Laval characteristics, wherein means set up to feed the first gas or gas mixture into the mixing chamber (11) through the passages (131) in a critical flow state are provided, and wherein one or more feed conduits (14) which have feed orifices (141) and extend into the mixing chamber (11) are provided for feeding of the second gas or gas mixture into the mixing chamber (11).