A method for causing chemical reactions between fluids, comprising the steps of arranging a plurality of metal sheets for providing first fluid flow channels adjacent to and in heat transfer contact with second fluid flow channels between adjacent ones of the metal sheets, placing catalyst material within at least some of the flow channels, passing a first fluid mixture through the first fluid flow channels and a second fluid mixture through the second fluid flow channels, wherein the first fluid mixture is different from the second fluid mixture, each fluid mixture undergoing separate reactions, one of the reactions being endothermic while the other reaction is exothermic, and causing heat to transfer between the adjacent fluid flow channels.