(564a) Novel Configured Pt/CeO2(core)@ZrO2(shell) Supported Three-Way Catalysts

Due to the vehicle engine efficiency improvement, catalysts need to perform effectively at low temperatures to meet the strict emission standards introduced by the Environmental Protection Agency. Therefore, U.S. DRIVE established a goal of achieving 90% conversion of hazardous emissions at 150 ºC; so-called “150 ºC challenge”. Fluctuations in the air to fuel ratio in stoichiometric gasoline engine aftertreatment systems result in a decreased efficiency of the catalytic converter.¹ CeO₂ is a promising catalyst support due to its high oxygen storage capacity (OSC) that buffers O₂ during rich/lean cycling.² However, CeO₂ suffers from poor thermal stability, indicated by its surface area loss from 50 (550 ^oC) to 2 m²/g (800 ^oC).⁴ A potential solution for improving the thermal stability of CeO₂ is incorporating ZrO₂ into CeO₂. Herein, CeO₂(core)@ZrO₂(shell) (Fig. 1(a)) structured supports were synthesized using a solvothermal method to synthesize CeO₂ spheres, followed by ZrO₂ shell deposition through hydrolysis and condensation of zirconium butoxide. Pt supported on commercial CeO₂, ZrO₂, CeO₂ spheres and Ce_0.7Zr_0.3O₂ solid solution (same composition as CeO₂@ZrO₂) were synthesized for comparison purposes. The catalytic performance was evaluated using the low temperature oxidation catalyst test protocol defined by U.S. DRIVE under stoichiometric gasoline direct injection (S-GDI) conditions.⁵ The T₉₀’s of CO, total hydrocarbons (THCs) and NO_x over hydrothermally aged 1.8 wt.% Pt/CeO₂@ZrO₂ were 228, 254 and 265 ^oC, respectively, lower than the CO, THCs and NO_x T₉₀’s over Pt/CeO₂ sphere (not able to achieve 90% conversion up to 500 ^oC). This observation confirms the performance improvement when Zr shell is incorporated on CeO₂ spheres (Fig. 1(b-d)). Besides, Pt/CeO₂@ZrO₂ outperformed Pt/Ce_0.7Zr_0.3O₂ (T₉₀’s at 339, 435 and >500 ^oC for CO, THC, and NO_x, respectively), suggesting the benefit of core@shell catalyst support configuration. Overall, this work illustrates the potential of developing CeO₂@ZrO₂ supported catalysts for stoichiometric gasoline oxidation reaction.