Plate exchanger reactor, for implementing endothermic or exothermic reactions, including: - a reactor body, formed by the stacking of a plurality of plates (10, 11, 12,13), - a reactive circuit comprising at least one reactive channel layer comprising a plurality of reactive channels extending substantially parallel with one another in a first direction, wherein a first reactive fluid circulates, - a heat transfer fluid circuit for cooling the reactive channels, comprising at least one cooling channel layer comprising a plurality of cooling channels extending substantially parallel with one another in a second direction, wherein a coolant circulates, the first and second directions are substantially perpendicular to one another, at least one reactive channel layer and a cooling channel layer are superimposed on one another alternately, the plate exchanger reactor includes at least one channel for injecting a second reactive fluid and at least one channel for distributing the second reactive fluid in at least one reactive channel wherein the first reactive fluid circulates, said at least one injection channel fluidically communicating with said at least one distribution channel by means of at least one injection opening and said at least one distribution channel fluidically communicating with said at least one reactive channel by means of a distribution opening, the distribution channel or channels are each located in a cooling channel layer and extending substantially parallel with the second direction, characterised in that a predetermined injection channel fluidically communicates with at least two distribution channels, which themselves fluidically communicate with at least two reactive channels so that an injection of the second reactive fluid by means of the predetermined injection channel makes it possible to supply a plurality of reactive channels of the same reactive channel layer. - a reactor body, formed by the stacking of a plurality of plates (10, 11, 12,13), - a reactive circuit comprising at least one reactive channel layer comprising a plurality of reactive channels extending substantially parallel with one another in a first direction, wherein a first reactive fluid circulates, - a heat transfer fluid circuit for cooling the reactive channels, comprising at least one cooling channel layer comprising a plurality of cooling channels extending substantially parallel with one another in a second direction, wherein a coolant circulates, the first and second directions are substantially perpendicular to one another, at least one reactive channel layer and a cooling channel layer are superimposed on one another alternately, the plate exchanger reactor includes at least one channel for injecting a second reactive fluid and at least one channel for distributing the second reactive fluid in at least one reactive channel wherein the first reactive fluid circulates, said at least one injection channel fluidically communicating with said at least one distribution channel by means of at least one injection opening and said at least one distribution channel fluidically communicating with said at least one reactive channel by means of a distribution opening, the distribution channel or channels are each located in a cooling channel layer and extending substantially parallel with the second direction, characterised in that a predetermined injection channel fluidically communicates with at least two distribution channels, which themselves fluidically communicate with at least two reactive channels so that an injection of the second reactive fluid by means of the predetermined injection channel makes it possible to supply a plurality of reactive channels of the same reactive channel layer.