The Effect of Fe and Other Promoters on the Activity of Pd/Ceria for the Water-Gas Shift Reaction

The effect of adding oxide promoters, at monolayer coverages, to Pd/ceria catalysts was studied for the water-gas-shift reaction in 25 torr each of H2O and CO under differential conditions. Oxides of Fe, Tb, Gd, Y, Sn, Sm, Pr, Eu, Bi, Cr, V, Pb, and Mo were added to ceria by wet impregnation of aqueous salts and calcined to 873 K prior to addition of 1 wt% Pd. While most of the oxides had a negligible effect on the water-gas-shift rates, rates on the Fe-promoted sample were 8 times higher than on the unpromoted Pd/ceria at 473 K, while rates on the Mo- and Pb-promoted cerias were significantly lower than on pure Pd/ceria. By varying the Fe loading, it was found that the maximum catalytic activity was achieved at the monolayer coverage. Addition of Fe in bulk ceria through sol-gel and preparation of Fe2O3-CeO2 physical mixtures had no effect on the catalytic activity