in situ IR Spectroscopic Investigation of Noble Metal Catalysts Related to the Reduction of Automotive Exhaust Emissions

The reduction of automotive exhaust emissions has been one of the hottest topics in catalysis community since 1970s. Thanks to the development of three-way catalysts, main auto-exhaust pollutants, such as carbon monoxide, nitrogen oxides and unburned hydrocarbons, can be removed simultaneously. Nowadays, diesel engines and lean-burn engines become more and more popular due to their high fuel-efficiency and low CO2 emissions. Unfortunately, conventional three-way catalysts are not effective at reducing NOx emissions from these engines due to excess oxygen in the exhaust stream. Platinum catalysts were found to be highly active for selective NO reduction with hydrocarbons in excess oxygen and has good thermal stability and sulfur resistance. However, discrepancies still exist in the reaction mechanism of NO reduction with hydrocarbons on platinum catalysts. In this thesis, fundamental surface science studies were performed with in situ IR spectroscopic techniques combined with mass spectrometry, aiming to gain some new insight into the catalysis related to auto-exhaust emission control. Three catalysts system were explored, including model catalysts Pt(100) single crystal and Ru/Al2O3 thin film supported nanoparticles, and powder catalyst Pt/Al2O3 with various particle sizes. It was demonstrated that polarization modulation infrared reflection absorption spectroscopy is highly effective at detecting surface species under reaction conditions and can be applied to bridge the “pressure gap” between surface science and industrial catalysis. In the meantime, model thin film supported catalysts were prepared via wet deposition method, which could be used to bridge the “materials gap”. Diffuse reflectance infrared fourier transform spectroscopy combined with mass spectrometry provided clear evidence of particle size effect on the formation of intermediate species over Pt/Al2O3 catalysts during the reaction of NO with propene, and a plausible mechanism was proposed. Thursday, September 24, 2015 1:00 PM Horizon 1 Building, Room 201