(660e) Atomic Layer Deposition of Ultrathin Al2O3-TiO2 Composite Film for Enhanced Catalytic Performance and Thermal Stability of Pt Catalysts

Sintering of sub-nanometer-size metallic catalyst in high temperature environment frequently occurs and substantially reduces the catalytic activity and stability because it decreases the catalytic surface area. Many approaches have been attempted to address this issue. Ultrathin overcoat layer deposition on the catalyst surface has been considered one of the promising methods to limit the movement of the catalytic metal particle, but the method has been often accompanied by the activity loss due to the inevitable covering of catalytic active sites. Herein, we demonstrate a strategy to overcome the trade-off relationship by enhancing both catalytic activity and thermal stability using atomic layer deposition (ALD). An ultrathin Al₂O₃/TiO₂ composite overcoat layer was deposited conformally onto Pt/γ-Al₂O₃ by using ALD method. A short aging step was adopted intermittently between cycles to allow an ALD precursor to penetrate sufficiently into the micro-structure of γ-Al₂O₃. Transmission electron microscopy (TEM) analysis confirmed that the overcoat layer effectively suppressed the sintering of Pt catalyst in a 2-hour incubation at 500 ℃, while considerable sintering was observed under the same treatment in the case of pristine Pt catalyst. To assess the catalytic activity of the Pt/γ-Al₂O₃, CO oxidation reaction was performed. The activity of Pt/γ-Al₂O₃ overcoated with the Al₂O₃/TiO₂ composite layer showed 10 % increase of the catalytic activity compared to that of the pristine Pt/γ-Al₂O₃. Such an improvement in catalytic activity presumably stems from the formation of the strong-metal-support-interaction (SMSI) between the metallic Pt particle and the Al₂O₃/TiO₂ composite overcoat. A precise engineering of the ALD process parameters and the optimization of the overcoat composition enabled to achieve the improvement in both the catalytic activity and the thermal stability against sintering at high temperature. This approach and methodology is expected to be able to serve as an important guideline for developing strategy for next-generation nanocatalyst design.