A catalyzer has a plurality of plane sheets arranged superposed and spaced apart from each other in a stack, between which a plurality of straight channels extend parallel in the flow direction and are delimited by the plane sheets. The plane sheets are coated in such a way that a catalytic coating is present in all channels; that the catalytic coating is limited to predetermined sections of the channels; and that inside the channels, uncoated sections in each case are positioned opposite to sections with the catalytic coatings. The uncoated sections absorb the heat radiation emitted by the catalytic coatings during operation, thereby improving cooling and preventing homogeneous ignition.