Exhaust purification of stoichiometric natural gas applications – A screening study on the impact of catalyst composition, reaction conditions and transient effects

A set of model catalysts with a variation of precious metal components comprising Pt, Pd or Pt/Pd on typical support materials (CeO 2 , Al 2 O 3 and ZrO 2 ) is evaluated in a gas mixture simulating the exhaust gas of stoichiometric natural gas-fueled engines. Three-way catalytic (TWC) performance, especially CH 4 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. NH 3 , N 2 O) on hydrothermally aged catalysts. Aging severity was introduced as additional dimension in the design of the experimental study. • The performance of Three-Way-Catalysts (TWC) for methane conversion was measured in dynamic tests on powder catalysts. • λ-sweep and dynamic light-Off tests with oscillating feed were run on an automated unit with a 12-fold catalyst exchanger. • 11 combinations of precious metal (Pt, Pd and Pt/Pd) and support materials (CeO 2 , Al 2 O 3 and ZrO 2 ) were evaluated after aging. • 3%Pt/CeO 2 outperformed other samples after 800 °C lean, 3%Pd/CeO 2 had highest methane conversion after 950° lean/rich aging. • No further advantage of using Pt and Pd together could be derived in the case of the ceria support. • The presence of water in the feed is essential for improved methane conversion at 450–500 °C and λ = 0.98–1.0. • The formation of H 2 indicated direct involvement of steam via water gas shift (WGS) or steam reforming). • Time resolved data from feed switch experiments show a high sensitivity of Pt catalysts towards oxygen content.