Effect of soot on the SCR reactions in an integrated SCR coated DPF

Louise  Olsson, Chalmers University

Effect of soot on the SCR reactions in an integrated SCR coated DPF

Oana Mihai1, Stefanie Tamm1, Marie Stenfeldt2 and Louise Olsson1*
1Chemical Engineering, Competence Centre for Catalysis, Chalmers University of Technology, SE- 412 96 Gothenburg, Sweden
2Volvo Cars Corporation, SE-405 31 Gothenburg, Sweden

It is a large advantage to combine after-treatment components in order to minimize the cost and packing volume. A promising way is to use a selective catalytic reduction (SCR) coated DPF, where SCR catalyst is coated on DPF substrate. The objective of this work was to examine the effect of soot on the SCR reactions as well as the effect of the SCR component on the soot removal.

A real SCR coated DPF (provided by a supplier) was loaded with soot using engine bench experiments (conducted at Volvo Cars) to study the behavior of the real soot on the SCR reactions. SCR-DPF samples (120 channels, 20 mm length) were cut from the large SCR-DPF and tested in a quartz reactor. Different catalyst samples were exposed to several different gas mixtures in order to study the effect of different reactions on the soot removal and the impact of soot on the reaction. The starting temperature was 150C and it was increased stepwise to 400C. Thereafter, the samples were cooled and the experiment was repeated from 150 to 500C, than 150 to 600C, 150 to 700C and 150 to 750C with cooling step in between, in order to study the gradual removal of soot. Examples of results from this study is that the NOx conversion was slightly lower at 200−300 °C during standard SCR conditions, due to the impact of soot, but at higher temperatures, the NOx conversion was slightly higher with soot. These results suggest that soot more strongly influenced the oxidation of NH3 than the SCR reaction. Interestingly, the presence of soot significantly decreased the formation or the stability of ammonium nitrate, resulting in higher conversion with soot and we propose that this occurs on cupper species on the outside of the zeolite particles.

This study has been a collaboration between Chemical Engineering at Chalmers University of Technology and Volvo Cars. Funding from the Swedish Energy Agency (FFI 37190-1) is gratefully acknowledged.

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