CO OXIDATION AND NO REDUCTION BY CO KINETICS OVER Rh/Al2O3 AND Pd/Al2O3
Silvia Marino, University of Virginia
Palladium and Rhodium are often used as active metals in commercial Three-Way Catalysts in order to remove NOx, CO and unburnt hydrocarbons simultaneously, operating under stoichiometric conditions. Stereotypically, Rh is used to attain high NO reduction rates, whereas Pd is very active for oxidation reactions.
An optimization of the catalyst design can be achieved by identifying and analyzing the differences between the two metals. Monometallic Rh and Pd aged catalysts supported on γ-alumina have been studied by performing steady-state measurements to calculate kinetic parameters. CO oxidation and NO reduction by CO in presence of water have been investigated under lean, stoichiometric and rich conditions.
The apparent activation energies calculated for CO oxidation reactions for both Rh and Pd correspond to the heat of adsorption of CO on the metals, indicating that at low temperatures both metals are covered by CO, inhibiting the dissociative adsorption of oxygen. However, at higher temperatures, Rh is characterized by different activation energies under lean and rich conditions. Similarly, activation energies for NO reduction by CO over Pd and Rh are different in different temperature regions, suggesting mechanistic changes.