Apparatus for providing a pure hydrogen stream for use with fuel cells

A thermosiphon shift reactor for conversion of carbon monoxide and generation of steam for use in a fuel processor comprising:

• a vertically extended shell defining an interior volume containing a vertical axis defining a catalyst zone, said catalyst zone comprising a high temperature shift catalyst disposed in a fixed bed having layers along the vertical axis from the top end to a point less than about 40% of the vertical length from the top end, wherein said layers comprise an inner core containing the high temperature shift catalyst and an outer ring comprising low temperature shift catalyst and the inner core is reduced from the top end to said point, said vertically extended shell having a gas inlet at a top end and a gas outlet at a bottom end opposite;
• a jacket sealingly surrounding the vertically extended shell along at least a portion of the vertical length of the catalyst zone and defining a flow passage between the vertically extended shell and the jacket, said jacket having an upper portion with a fluid outlet and a lower portion with a fluid inlet;
• an insulating layer disposed on the vertically extended shell within the flow passage;
• and
• a fluid reservoir located at a height effective to provide thermosiphon circulation through said flow passage, said fluid reservoir having an inlet conduit in fluid communication with the fluid outlet, a water supply inlet, and an outlet conduit in fluid communication with the fluid inlet of the jacket.