Adatom Emission From Nanoparticles: Implications for Ostwald Ripening
To achieve clean air in our cities, all modern means of ground transportation make use of catalytic converters. Precious metal-based catalysts such as Pt and Pd are currently used in catalytic converters. To achieve higher fuel efficiency, combustion can be carried out in excess air resulting in a reduction of greenhouse gas (GHG) emissions. Reduction of these emissions has emerged as a major challenge. Most of the pollutants are emitted within the first 30 seconds after starting an engine because the catalyst is cold. The development of catalysts which achieve high activity at low temperatures will improve fuel efficiency and therefore reduce the nations dependence on foreign fossil fuels. The supplies of precious metals are limited worldwide, but there is increasing demand for clean energy. Therefore, there is a need to develop more active catalysts that provide long-term stable performance at elevated temperatures with minimal use of precious metals such as platinum. A major problem is that catalysts lose activity during use. Pt particles sinter, leading to poor stability. There is universal agreement that addition of Pd improves the catalytic performance as well as the durability of the Pt catalysts; however, the mechanisms by which Pd improves the performance of Pt are less clear. Conventional supported catalysts (Pt, Pd, and Pt-Pd) have been used to explore the microstructure of diesel oxidation catalysts (DOCs) in their working state (i.e. under oxidizing conditions). Model catalysts have been used to study the evolution of platinum and palladium nanoparticles. Both a statistical and a microscopic approach have been used to understand the ways in which Pd affects Pt. The catalytic activity and kinetics of various monometallic as well as bimetallic powder catalysts aged under different conditions has also been studied. NO oxidation in the presence of NO, O2, and NO2 was the probe reaction used to distinguish between the differing activities of Pt/Al2O3 and Pt-Pd/Al2O3. The work described here focuses on important problems in the field of catalysis. A fundamental understanding of the role of palladium on both the catalytic activity and long-term performance of platinum catalysts has been gained.'
bimetallic PtPd catalysts, Ostwald ripening, sintering, diesel oxidation, EXAFS, vapor phase emission
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