Hybrid water gas shift system

A fuel processing system (FPS) ( 120, 220, 320 ) provides a hydrogen-rich reformate having a reduced level of CO ( 34, 234, 62 ), as for use in a fuel cell power plant ( 120 ). The FPS includes, in combination, a reformer ( 30, 230 ) for converting hydrocarbon feedstock ( 22 ) to reformate and a multistage hybrid WGS reactor ( 150, 250, 350 ) for converting CO with H2O in the reformate to H2 and CO2 to reduce the CO in the reformate. The multistage hybrid WGS reactor ( 150, 250, 350 ) has one stage ( 154, 254, 352 ) of active noble metal catalyst ( 174, 274, 374 ), typically platinum and/or rhenium, and an other stage ( 152, 252, 354 ) of Cu-based WGS catalyst ( 172, 272, 372 ), e.g. Cu/ZnO, whereby the collective volume of the one and the other stages is relatively small, being less than about ½ that of prior WGS reactors. The Cu-based WGS catalyst may be modified to reduce self-heat. Protection from sulfur in the reformate is also provided. The multistage hybrid WGS reactor ( 150, 250, 350 ) may further include an O2 guard.