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A set of model catalysts with a variation of precious metal components comprising Pt, Pd or Pt/Pd on typical support materials (CeO2, Al2O3 and ZrO2) is evaluated in a gas mixture simulating the exhaust gas of stoichiometric natural gas-fueled engines. Three-way catalytic (TWC) performance, especially CH4 conversion, is assessed in λ-sweep as well as dynamic light-Off/light-Out tests, both with oscillating feed (1 s lean /1 s rich) implemented on a fully automated reactor system. The transient response of catalysts to changing redox potential is demonstrated in tests with varying lean/rich duration and pseudo-stationary tests. Time resolved data clearly indicate that performance and stability depend on both, precious metal composition as well as support material. Beyond screening of catalyst activity, the focus was on factors affecting the formation of undesired by-products (e.g. NH3, N2O) on hydrothermally aged catalysts. Aging severity was introduced as additional dimension in the design of the experimental study.
Sundermann et al. (Tue,) studied this question.