CO and hydrocarbon light-off inhibition by pre-adsorbed NOx on Pt/CeO2/Al2O3 and Pd/CeO2/Al2O3 diesel oxidation catalysts

A Bifunctional Pt/CeO2-Cu1/CeO2 Catalyst System for Isooctane Oxidation under Fully Simulated Engine-Exhaust Condition: Eliminating the Inhibition by CO

Pt-based catalysts, because of their outstanding activity for hydrocarbon oxidation, are widely used in the engine-exhaust aftertreatment system to remove hydrocarbon emissions. However, the CO and NOx present in real engine exhausts compete with hydrocarbons for active Pt sites, and thus inhibit hydrocarbon oxidation. In this work, we evaluated the inhibition effects of CO and NO on isooctane oxidation over a Pt/CeO2 catalyst under the simulated condition of the US DRIVE test protocol (S-GDI, stoichiometric gasoline direct injection). We also leveraged a low-cost single-atom Cu1/CeO2 catalyst, which is highly active for low-temperature CO oxidation, to eliminate the inhibition effect of CO. Specifically, by physically mixing Cu1/CeO2 and Pt/CeO2, all the CO is completely converted below 200 °C under simulated exhaust condition, which helps lower the isooctane oxidation temperature. However, the unconverted NO still strongly suppresses HC oxidation. Possible strategies to address the NO inhibitor were proposed.

Self-Regeneration Process of Ni-Cu Alloy Catalysts during a Three-Way Catalytic Reaction-An Operando Study

It is important to understand the reduction processes of mixed metal oxides or metal oxide interfaces in three-way catalytic reactions toward replacing the currently used high-cost Pt group metal catalysts. The redox behavior of simple Ni-Cu alloy catalysts, which exhibit high catalytic activity and durability during a three-way catalytic reaction, was studied by operando X-ray absorption spectroscopy (XAS). The operando XAS analyses revealed that Ni-Cu species changed from the NiO-Cu₂O to Ni-Cu alloy and vice versa under reductive and oxidative conditions, respectively. The real-time monitoring of the oxidation states of Ni and Cu species indicated that the Cu species assisted the reduction of Ni species, in agreement with the density functional theory-based study of NiO reduction by carbon monoxide in the presence of metallic Cu nanoparticles.