A shell-and-tube heat exchange reactor for carrying out a catalytic gas-phase partial oxidation reaction comprises a shell-side heat exchange passage for circulating a heat transfer medium and a reaction passage comprising a plurality of reaction tubes; an inlet for introducing the reactant stream to the reaction passage; and an outlet from the reaction passage for recovering an effluent stream from the reaction tubes. The reaction tubes comprise a reactant pre-heating zone adjacent to the inlet, and a reaction zone downstream of the reactant pre-heating zone, the reaction zone having a catalytically active wire matrix insert having at least on a part of its surface a catalytically active precious metal. The reactor requires less frequent maintenance in the form of regeneration and/or replacement of the catalyst. The catalyst can be easily placed into the reaction tubes, and be removed therefrom. Only the portion of the entire reactant stream that travels near the hot reaction tube wall is heated up. Consequently, the portion of the reactant stream flowing in the center of the reaction tube is not heated to the reaction temperature and blind reactions of the unstable starting materials are thus reduced or even avoided.