Oxygen-enhanced water gas shift on ceria-supported Pd–Cu and Pt–Cu bimetallic catalysts

Abstract

Aiming at enhancing H 2 production in water gas shift (WGS) for fuel cell application, a small amount of oxygen was added to WGS reaction toward oxygen-enhanced water gas shift (OWGS) on ceria-supported bimetallic Pd–Cu and Pt–Cu catalysts. Both CO conversion and H 2 yield were found to increase by the oxygen addition. The remarkable enhancement of H 2 production by O 2 addition in short contact time was attributed to the enhanced shift reaction, rather than the oxidation of CO on catalyst surface. The strong dependence of H 2 production rate on CO concentration in OWGS kinetic study suggested O 2 lowers the CO surface coverage. It was proposed that O 2 breaks down the domain structure of chemisorbed CO into smaller domains to increase the chance for coreactant (H 2O) to participate in the reaction and the heat of exothermic surface reaction helping to enhance WGS kinetics. Pt–Cu and Pd–Cu bimetallic catalysts were found to be superior to monometallic catalysts for both CO conversion and H 2 production for OWGS at 300 °C or lower, while the superiority of bimetallic catalysts was not as pronounced in WGS. These catalytic properties were correlated with the structure of the bimetallic catalysts. EXAFS spectra indicated that Cu forms alloys with Pt and with Pd. TPR demonstrated the strong interaction between the two metals causing the reduction temperature of Cu to decrease upon Pd or Pt addition. The transient pulse desorption rate of CO 2 from Pd–Cu supported on CeO 2 is faster than that of Pd, suggesting the presence of Cu in Pd–Cu facilitate CO 2 desorption from Pd catalyst. The oxygen storage capacity (OSC) of CeO 2 in the bimetallic catalysts indicates that Cu is much less pyrophoric in the bimetallic catalysts due to lower O 2 uptake compared to monometallic Cu. These significant changes in structure and electronic properties of the bimetallic catalysts are the result of highly dispersed Pt or Pd in the Cu nanoparticles.