Comparison of Pd/LTA and Pd/SSZ-13 as passive NOx adsorbers (PNA)

Louise  Olsson, Chalmers University of Technology

Comparison of Pd/LTA and Pd/SSZ-13 as passive NOx adsorbers (PNA)

Aiyong Wang 1, Kristina Lindgren 2, Mengqiao Di 3, Diana Bernin 1, Per-Anders Carlsson 3, Mattias Thuvander 2, Louise Olsson 1

1Competence Centre for Catalysis, Chemical Engineering, Chalmers University of Technology, Gothenburg, SE 412 96, Sweden
2Department of Physics, Gothenburg, SE 412 96, Sweden
3Competence Centre for Catalysis, Applied Chemistry, Chalmers University of Technology, Gothenburg, SE 412 96, Sweden

Abstract

We have compared Pd/LTA and Pd/SSZ-13 as passive NOx adsorbers (PNA). For degreened samples the storage was about 20% higher for Pd/LTA compared to Pd/SSZ-13 in the presence of 200ppm CO.  The adsorbers were further evaluated during hydrothermal aging at 750, 800, 850, and 900C. The structure of Pd/LTA was remarkably stable also after hydrothermal aging at 900C, where a clear degradation of the structure was observed for Pd/SSZ-13. The Pd species were however, also influenced for Pd/LTA after hydrothermal aging, resulting in a lowering of the storage capacity. Interestingly, the decrease in storage after hydrothermal aging was lower for Pd/LTA compared to Pd/SSZ-13, which lead to that the NOx storage after hydrothermal aging at 900C was 45% higher for Pd/LTA. In order to understand the differences observed between Pd/LTA and Pd/SSZ-13 detailed characterization was performed using ICP, BET, XRD, O2-TPD, NH3-TPD, NMR, APT, TEM, HAADF-STEM and in situ DRIFTS.