Co-oxidation of CO and propylene on Pd/CeO2-ZrO2 and Pd/Al2O3 monolith catalysts: A light-off, kinetics, and mechanistic study

Abstract

The light-off (ignition) and steady-state behavior for individual oxidation and co-oxidation of CO and propylene under near-stoichiometric conditions was studied using Pd/Al2O3 and Pd/CeO2-ZrO2 monolith catalysts. CO and propylene are shown to be self- and mutually-inhibiting, with inhibition mitigated by the promotional effect of CeO2-ZrO2. Oxidation is enhanced at low temperatures for CO, and at intermediate and high temperatures for propylene. Light-off behavior during CO and propylene co-oxidation is similarly improved at low and high temperatures. Steady-state differential kinetics measurements using Pd/Al2O3 show reaction orders of ∼−1 with respect to CO and propylene. Using Pd/CeO2-ZrO2, the reaction order with respect to CO shifts towards zero and the activation energy decreases, suggesting an alternate reaction mechanism for CO oxidation when enough ceria is present. Mechanisms for CO and propylene oxidation that are consistent with the kinetics and inhibition trends are presented.