(570b) Pt-CeO2-Al2O3 Nanosheet Catalysts with Enhanced Lean/Rich Hydrothermal Aging Stability for Twc Applications

Three-way catalysts (TWCs), which can simultaneously oxidize carbon monoxide (CO), total hydrocarbons (THCs), and reduce nitrogen oxides (NO_x) at temperatures > 350 ^oC, have been successful for gasoline vehicle emission control in the past decades. However, with the development of highly efficient engines (lower emission temperatures) and increasing cost of Rh, developing new Rh-free TWCs with enhanced low temperature activity and lean/rich hydrothermal stability is highly desirable.

Herein, a series of Rh-free TWCs containing 1 wt.% Pt supported on CeO₂ nanocrystals anchored by penta-site rich γ-Al₂O₃ nanosheets (AlNS) were synthesized and evaluated under a simulated gasoline vehicle exhaust stream (U.S. DRIVE).¹ The catalytic performance of Pt-Ce-AlNS (CeO₂ loading: 10-80 wt.%) after a harsh lean/rich hydrothermal aging (800 ^oC/10h) is shown in Fig. 1. State-of-the-art Rh-based catalyst (0.5 wt.% Rh-12wt.% TiO₂-Al₂O₃ (Rh-Ti-Al)) was also tested for comparison.² Increasing the CeO₂ loading from 0-60 wt.% led to a decrease in the T₉₀ for NO_x, CO and THC from 446 (NO_x), 439 (CO), 439 ^oC (THC) to 241 (NO_x), 192 (CO), 236 ^oC (THC) (Fig.1 (a-c)). Pt-Ce-AlNS catalysts showed a comparable performance to the state-of-the-art Rh-based catalysts that has T₉₀’s equal to 264 (NO_x), 184 (CO), 265 ^oC (THC). Further increase in the CeO₂ loading to 80 wt.% led to a slight decrease in performance. The Pt-Ce-AlNS catalysts showed a significantly enhanced lean/rich hydrothermal aging stability compared to Pt-CeO₂ and Pt-Al₂O₃ catalysts. H₂-TPR results indicated that there is a strong interaction between CeO₂ and AlNS that is maximized at CeO₂ loading of 60 wt.%. BET and XRD results showed that the CeO₂ nanocrystal grain growth slows down by AlNS incorporation. This work illustrates that CeO₂ deposition on the surface of penta-site rich γ-Al₂O₃ nanosheets can remarkably enhance the catalyst stability upon lean/rich hydrothermal aging.