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The last generation of catalysts for automotive emissions has substituted the traditional ceria by cerium-zirconium mixed oxides, due to their increased oxygen storage capacity, selectivity to the desired products (mostly N2) and durability; while increasing the proportion of palladium, due to its interesting behavior. Using simplified feed-streams with only three components: propylene, NO and O2, plus the N2 carrier, and with data of integral reactor in the range 200300ºC, we have performed experiments in order to obtain kinetic data with a 0.5 %Pd/Ce0.68Zr0.32O2 catalyst. The results have shown that, in the studied range, inlet reaction rates of reactants consumption and products formation can be explained by a Mars-Van Krevelen mechanism in which O2 and NO oxidize the support, and products formation takes place via reduction of the support by the rest of the reactants. Net formation of NO is observed in the low-temperature range, while the opposite is truth in the high-temperature range. Although this behavior has no effect during normal operating conditions in the automobile, it could during cold start up. Also, it is interesting to note that, at low temperature, a significant amount of NH3 decreasing with temperature and some N2O with a maximum at intermediate temperature (around 275ºC) are formed even though the conditions were highly oxidizing, provided that C3H6 is present. NO, on the other hand, is the precursor for NO2.

Pd Supported on Ce/Zr Mixed Oxides in the Reduction of NO with Propylene in Oxidizing Conditions