A catalytic reactor (40) comprises a plurality of sheets (42) defining flow channels (44) between them. Within each flow channel (44) is a foil (46) of corrugated material whose surfaces are coated with catalytic material apart from where they contact the sheets (44). At each end of the reactor (40) are headers to supply gas mixtures to the flow channels (44), the headers communicating with adjacent channels being separate. The reactor (40) enables different gas mixtures to be supplied to adjacent channels (44), which may be at different pressures, and the corresponding chemical reactions are also different. Where one of the reactions is endothermic while the other reaction is exothermic, heat is transferred through the sheets (42) separating the adjacent channels (44), from the exothermic reaction to the endothermic reaction. The reactor (40) may be used in a compact plant to perform steam/methane reforming, obtaining the necessary heat by catalytic methane combustion, and also for Fischer-Tropsch synthesis, so that the overall process involves conversion of methane to long-chain hydrocarbons.