(105d) Self-Assembly of Nanostructured Metal Alloys in Low Temperature Oxidation Catalysis

There is a recognized need for lowering greenhouse gas emissions from mobile sources in order to address concerns regarding global climate change. Advanced combustion engine technologies offer significant improvement in fuel economy as well as lower NOx emissions inherent in the nature of low temperature combustion; however the low exhaust temperatures in such systems raise a major concern regarding the removal of other air pollutants such as hydrocarbon and CO emissions in an increasingly stringent regulatory environment.  In particular, exhaust gas temperatures from advanced combustion technologies can be well below 200 °C.  Currently, precious metal-based catalysts such as platinum (Pt) and palladium (Pd) are most commonly used for carbon monoxide and hydrocarbon oxidation in gasoline and diesel engines.

The present study illustrates that physically mixed monometallic Pt/Al₂O₃ and Pd/Al₂O₃ catalysts – most commonly used automotive catalysts for low temperature oxidation – form well-defined Pt–Pd alloys after hydrothermal aging, and the alloyed system shows significant improvement in both activity and stability compared to the monometallic Pt and Pd catalysts.  The structures of self assembling noble metal particles are confirmed by aberration corrected scanning transmission electron microscopy (STEM), x-ray diffraction (XRD) and extended x-ray absorption fine structure (EXAFS) experiments.