Influence of controlled spatial deposition of Pt and Pd in NOx storage-reduction catalysts on their efficiency

Abstract Catalysts for NO x storage and reduction (NSR) were prepared with a twin flame spray pyrolysis (FSP) unit allowing the preferential deposition of Pd and/or Pt nanoparticles on the catalyst's storage (K 2 CO 3 ) or support (Al 2 O 3 ) components. The structural properties of the catalysts were characterized by nitrogen adsorption, CO chemisorption combined with diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), X-ray diffraction, and electron microscopy. Various combinations with Pt and Pd either deposited on the storage component (K 2 CO 3 ) or the support (Al 2 O 3 ) were tested by fuel lean/rich cycling exhibiting NO x conversion above 90% at 300 °C. At 250 °C the best performance was achieved when Pt was deposited on K 2 CO 3 , whereas Pd was more active when deposited on Al 2 O 3 , albeit the activity of Pd to reduce NO x was low. Mixing Pd with Pt, that is depositing both noble metals on the same component (storage component or support), lowered the NO x conversion, in some cases even below that of Pt only catalysts. In Pt/Pd/Ba/CeO 2 catalysts, where Pd was deposited on the Ba storage component and Pt on the CeO 2 support, Pd became active above 300 °C showing best reduction performance. At these temperatures Pt/Pd/Ba/CeO 2 catalysts where the two noble metals were separated by deposition on the storage and support components showed superior behavior compared to corresponding single noble metal catalysts.

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