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University of California-Los Angeles, Los Angeles, CA
New advances in combinatorial methodologies are exploited for the discovery and optimization of nanostructured catalytic materials for the reduction of NOx under fuel lean combustion conditions. Recent developments in automotive engineering have made possible the production of more fuel efficient-up to 25 percent-lean burning gasoline engines. However, the lack of appropriate catalytic technology to reduce NOx emissions under lean burn conditions impedes the commercialization of such engines. Although the existing three-way catalysts allow for the effective control of CO, hydrocarbon (HC) and NOx emissions in current gasoline engines that operate under stoichiometric conditions, they are ineffective in the presence of excess oxygen encountered in lean-burn engine exhausts. Therefore, the development of a new generation of catalysts that will allow NOx control in oxygen rich environments is urgently needed.
In the current program, libraries of catalytic materials were prepared by individually impregnating five support materials of Al2O3, CeO2, SiO2, TiO2, and Y-ZrO2 by salt solutions of 42 elements from the periodic table into resulting in five different metal loadings. These support materials were used because of their durability in harsh engine exhaust conditions. Catalytic materials were then tested for their NO reduction activities using array channel microreactors and mass spectrometry. Overall, several thousand catalytic materials were prepared and then tested at 1 atm pressure and in the temperature range 100 to 500 C, and at a GSHV of 60,000 h-1. The feed gas used was 500 ppmv NO, 500 ppmv C3H6, 1400 ppmv CO, 8 percent O2, 10 percent H2O, and the balance helium. These test conditions realistically simulate the actual engine-out conditions, thereby rendering our findings immediately relevant to automobile exhaust treatment catalysis. These systematic investigations led to the discovery of Pt/TiO2 and Pt/SiO2 as the most significant leads, both of which exhibited superior performances, reducing the levels of NO by 25 percent and 20 percent, respectively.