Performance of dynamic oxygen storage capacity, water–gas shift and steam reforming reactions over Pd-only three-way catalysts

Abstract

The catalytic performances of Pd/CeO 2, Pd/Ce 0.67Zr 0.33O 2, and Pd/Ce 0.67Zr 0.33O 2-Al 2O 3 three-way catalysts are evaluated through dynamic oxygen storage pulses (DOSC), water–gas shift reactions (WGS), and steam reforming reactions (SR). Despite the differences in the morphologies and chemical compositions of the catalysts, the very similar mechanisms over the three samples for the above reactions have been confirmed according to the compensation effect. Oxygen migration ability plays a key role in DOSC activities. The dynamic oxygen storage rates (DOSR) are ordered as: Pd/Ce 0.67Zr 0.33O 2-Al 2O 3 > Pd/Ce 0.67Zr 0.33O 2 > Pd/CeO 2. The synergetic effect of ceria contents, oxygen vacancies, and precious metal dispersion determines the activity of WGS reaction. The orders of light-off temperatures are as follows: WGS-fresh: Pd/CeO 2 < Pd/Ce 0.67Zr 0.33O 2-Al 2O 3 < Pd/Ce 0.67Zr 0.33O 2; WGS-aged: Pd/Ce 0.67Zr 0.33O 2-Al 2O 3 < Pd/CeO 2 < Pd/Ce 0.67Zr 0.33O 2. For SR reactions, oxidized states of palladium particles and less acidity of support oxides can be beneficial. Thus the light-off temperatures are ordered as: SR-fresh: Pd/Ce 0.67Zr 0.33O 2 < Pd/CeO 2 < Pd/Ce 0.67Zr 0.33O 2-Al 2O 3; SR-aged: Pd/CeO 2 < Pd/Ce 0.67Zr 0.33O 2-Al 2O 3 < Pd/Ce 0.67Zr 0.33O 2.