FTIR analysis of supported catalyst systems related to the reduction of automotive exhaust emissions
Abstract
Fourier transform infrared spectroscopy and mass spectrometry were used in tandem to investigate the surface chemistry and reactivity of three different catalyst systems. The three systems were related by their relevance to current issues in automotive exhaust catalysis and the fact that each system operated under non-steady state conditions. In the first system, isothermal kinetic rate oscillations in the oxidation of carbon monoxide were studied on a series of silica-supported platinum catalysts. It was determined that the oscillations are related to the formation of densely packed islands on the surface of the catalyst that poison a portion of the active sites and that change in dimension during the course of the reaction. The origin of this effect is unknown, but it may be related to the surface phase transition that is responsible for oscillations in the same reaction on platinum single crystals. Second, isothermal kinetic rate oscillations were also studied in the decomposition of nitrous oxide over copper-exchanged ZSM-5 zeolite. In this case, the oscillations were linked to the existence of a nitrate species bound to isolated copper ions associated with the zeolite framework. Catalysts made from aluminum-rich ZSM-5 did not show oscillations due to a de-stabilization of the critical nitrate species under reaction conditions. Finally, a fundamental study of a new class of materials known as nitrogen storage and reduction (NSR) catalysts was performed. These catalysts are designed to remove nitrogen oxides from automotive exhaust in the presence of excess oxygen if the engine is operated in a transient fashion such that the fuel mixture is cycled between a fuel-rich phase and a fuel-lean phase. Many details of the reaction mechanism were uncovered. It was found that interaction between the reactive platinum component and the barium oxide storage component is critical to the activity of the catalyst due to the need for spillover between the two phases. In addition, the use of iron as an additive to the catalyst system was shown to improve the durability of the material to poisoning by sulfur compounds.
Degree
Ph.D.
Advisors
Lauterbach, Purdue University.
Subject Area
Chemical engineering|Environmental engineering|Automotive materials
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