The Activity of Fe-Pd Alloys for the Water-Gas Shift Reaction
The role of Fe promoters has been investigated on Pd/ceria, Pt/ceria and Rh/ceria catalysts for the water-gas shift (WGS) reaction in 25 Torr of CO and H2O, under differential reaction conditions. While no enhancement was observed with Pt and Rh, the activity of Pd/ceria increased by as much as an order of magnitude upon the addition of an optimal amount of Fe. Similarly, the addition of 1 wt% Pd to an Fe2O3 catalyst increased the WGS rate at 453 K by a factor of 10 over that measured on Fe2O3 alone, while the addition of Pt or Rh to Fe2O3 had no effect on rates. The amount of Fe that was necessary to optimize the rates increased with Pd loading but was independent of the order in which Fe and Pd were added to the ceria. Increased WGS activity was also observed upon the addition of Fe to Pd supported on Ce0.5Zr0.5O2. XRD measurements, performed after running the catalyst under WGS conditions, show the formation of a Fe-Pd alloy, even though similar measurements on an Fe/ceria catalyst showed that Fe3O4 was the stable phase for Fe in the absence of Pd. Possible implications of these results on the development of new WGS catalysts are discussed.