Shift converter having an improved catalyst composition

Abstract

A shift converter ( 16 ) in a fuel processing subsystem ( 14, 16, 18 ) for a fuel cell ( 12 ) uses an improved catalyst composition ( 50 ) to reduce the amount of carbon monoxide in a process gas for the fuel cell ( 12 ). The catalyst composition ( 50 ) is a noble metal catalyst having a promoted support of mixed metal oxide, including at least both ceria and zirconia. Cerium is present in the range of 30 to 50 mole %, and zirconium is present in the range of 70 to 50 mole %. Additional metal oxides may also be present. Use of the catalyst composition ( 50 ) obviates the requirement for prior reducing of catalysts, and minimizes the need to protect the catalyst from oxygen during operation and/or shutdown.

What is claimed is:  
     
         1 . A shift converter ( 16 ) for reducing the amount of carbon monoxide in a process gas ( 20 ,  24 ) using a water gas shift reaction, the shift converter ( 16 ) having a catalyst chamber ( 32 ), the chamber ( 32 ) having an inlet ( 36 ) for entry of the process gas into the chamber, an outlet ( 38 ) downstream of the inlet for exit of effluent from the chamber, and a catalyst composition ( 50 ) located between the inlet ( 36 ) and the outlet ( 38 ) for converting at least a portion of the carbon monoxide and water in the process gas into carbon dioxide and hydrogen, the improvement wherein the catalyst composition ( 50 ) in the catalyst chamber ( 32 ) comprises: 
 a noble metal catalyst having a promoted support, said promoted support comprising a mixed metal oxide of at least cerium oxide (ceria) and zirconium oxide (zirconia).    
     
     
         2 . The shift converter ( 16 ) of  claim 1  wherein, in the mixed metal oxide, the amount of cerium present is in the range of 30 to 50 mole % and the amount of zirconium present is in the range of 70 to 50 mole %.  
     
     
         3 . The shift converter ( 16 ) of  claim 1  wherein the noble metal of the catalyst composition ( 50 ) is selected from the group consisting of platinum, palladium, rhodium, and gold.  
     
     
         4 . The shift converter ( 16 ) of  claim 3  wherein the noble metal of the catalyst composition ( 50 ) is platinum.  
     
     
         5 . The shift converter ( 16 ) of  claim 1  wherein the metal oxide comprising the promoted support additionally includes at least a third metal oxide.  
     
     
         6 . The shift converter ( 16 ) of  claim 5  wherein the third metal oxide is selected from the group consisting of praseodymium oxide, lanthanum oxide, neodymium oxide, and hafnium oxide.  
     
     
         7 . The shift converter ( 16 ) of  claim 1  wherein at least the promoted support of the catalyst composition ( 50 ) is wash-coated onto a supporting substrate, and further including alumina mixed with the promoted support to facilitate adhesion of the wash-coat onto the supporting substrate.  
     
     
         8 . The shift converter ( 16 ) of  claim 1  wherein the catalyst composition ( 50 ) operates independent of any requirement for prereduction, a shutdown purge, or an inerting atmosphere.  
     
     
         9 . The shift converter ( 16 ) of  claim 1  wherein the shift converter ( 16 ) is operatively connected in a fuel processing subsystem ( 14 ,  16 ,  18 ) for a fuel cell ( 12 ).  
     
     
         10 . The shift converter ( 16 ) of  claim 8  wherein the shift converter ( 16 ) is operatively connected in a fuel processing subsystem ( 14 ,  16 ,  18 ) for a fuel cell ( 12 ) and the process gas includes hydrogen.