Palladium, zeolite, ceria based passive NOx adsorbers

Louise  Olsson, Chalmers University

Palladium, zeolite, ceria based passive NO_x adsorbers

Oana Mihai, Lidija Trandafilovic, Francesc Fluxa Torres, Travis Wentworth and Louise Olsson*

Competence Centre for Catalysis, Chemical engineering, Chalmers University of Technology, Gothenburg, SE 412 96, Sweden

*Corresponding author: louise.olsson@chalmers.se (L. Olsson).

In this work passive NO_x adsorbers (PNA) are studied. The NO_x should be stored in the PNA at low temperature where the selective catalytic reduction (SCR) catalyst is not functioning and thermally release the NO_x at high temperature. We have examined Ce/Pd/Al₂O₃ as a base catalyst. However, this sample release 81% of the NO_x at temperatures below 200°C, where urea dosing for the SCR is difficult. We therefore examined the effect of supporting the Pd on zeolites (SSZ-13 and BEA). In addition, we prepared Ce/Pd/zeolites, which to our knowledge has not been shown in literature for PNA applications earlier. When comparing, the NO_x desorbed between 200-400°C, the Pd/SSZ-13 released significantly more NO_x than Ce/Pd/Al₂O₃. This release is up to 400°C, which might be a bit high in temperature. Interestingly, the addition of 5% ceria to the sample resulted in that the desorption peak was shifted from 322 to 292°C, which could be beneficial. In addition, the desorption peak increased with 11% in the region 200-400°C. Increasing the ceria concentration further for the Ce/Pd/SSZ-13 resulted in a decreased desorption above 200°C, which also was the case if BEA was used instead of SSZ-13.