NOVELTY - A catalytic reactor (40) has metal sheets (42) arranged to define gas flow channels (A) (44) between the sheets, unit for defining gas flow channels (B) arranged to ensure good thermal contact within gases in the flow channels, permeable metal heat transfer layer (46) within each flow channel and headers for supplying gas mixtures to flow channels.    USE - For performing methane/steam reforming and gas-phase reactions at elevated temperatures, such as highly exothermic and endothermic reactions.    ADVANTAGE - Thermal contact between the gases in gas flow channel is improved. The formation of methane is suppressed due to the absence of catalyst material at the bottom of the troughs of the corrugations.    DETAILED DESCRIPTION - A catalytic reactor (40) has metal sheets (42) arranged to define gas flow channels (A) (44) between the sheets, unit for defining gas flow channels (B) arranged to ensure good thermal contact within gases in the flow channels, permeable metal heat transfer layer (46) within each flow channel and headers for supplying gas mixtures to flow channels. The heat transfer layer is removable and has catalytic coating at least in channel (A). If the catalytic coating incorporates a ceramic layer the coating is provided only on the surfaces of the heat transfer layer which do not come into contact with the walls of the channel. INDEPENDENT CLAIMS are included for:    (1) Process for performing methane-steam reforming using a catalytic reactor; and    (2) Plant for processing methane to produce longer chain hydrocarbons. The plant has catalytic reactor (I) for performing steam/methane reforming, catalytic reactor (II) for performing Fisher-Tropsch synthesis, unit for transferring products from reactor (I) to reactor (II) and unit for condensing liquid components of fluid mixture resulting from Fischer-Tropsch synthesis. The transfer unit has heat exchanger(s) to remove heat from the products and compressor(s) for increasing the pressure of the products.    DESCRIPTION OF DRAWING(S) - The figure shows the cross-sectional view of catalytic reactor.    Catalytic reactor ((40)    Metal sheet (42)    Gas flow channel (44)    Heat transfer layer (46)