Directing exhaust gas around a catalyst may pre-heat the catalyst and may thereby bring the catalyst quickly in its operating temperature range. An exhaust gas treatment system for treating the exhaust gas may include a first flow path, a second flow path, and a control system. The first flow path may include a catalyst. The second flow path may be coaxially arranged in heat exchange relation with respect to the first flow path. The control system may be configured to control the flow of exhaust gas through the first flow path or the second flow path dependent upon the catalyst temperature.