A catalytic converter reactor having in-built catalytic converter modules, wherein the total flow impingement surface area provided by the catalytic converter elements fitted in the catalytic converter modules is larger than the flow impingement surface area of the catalytic converter reactor, the module impingement surface area being defined by the catalytic converter module surfaces facing the main flow direction, and the catalytic converter modules being positioned so that the waste gas flows through the catalytic converter elements contained therein in a direction different from the flow direction on the intake and exit sides.