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Coupled NOx storage and reduction and selective catalytic reduction using dual-layer monolithic catalysts

Paper ID Volume ID Publish Year Pages File Format Full-Text
46196 46433 2012 13 PDF Available
Title
Coupled NOx storage and reduction and selective catalytic reduction using dual-layer monolithic catalysts
Abstract

Lean reduction of NOx (NO and NO2) was studied using monolith-supported catalysts consisting of a layer of a metal-exchanged (Fe, Cu) zeolite (ZSM-5) selective catalytic reduction (SCR) catalyst deposited on top of a Pt/Rh/BaO/CeO2 lean NOx trap (LNT) catalyst. During periodic switching between lean and rich feeds, the LNT layer reduces NOx to N2 and NH3. The SCR layer traps the latter, resulting in additional NOx reduction. The dual-layer catalysts exhibited high N2 selectivity and low NH3 selectivity over the temperature range of 150–300 °C. The NOx conversion was incomplete due to undesired side reactions in the LNT layer, such as NH3 oxidation to N2O at low temperature and NOx at high temperature. The NOx conversion and N2 selectivity of the Cu-exchanged ZSM-5 was higher than that of the Fe-exchanged ZSM-5. This was due to a higher low temperature SCR activity and a higher NH3 storage capacity on the Cu-zeolite. The dual-layer catalyst had a higher NOx conversion than the LNT catalyst below 300 °C and a higher N2 selectivity over the entire temperature range when H2O and CO2 were present in the feed. The NOx storage capacity and NH3 generation increased upon addition of CeO2 to the LNT layer below 250 °C. It also led to increased NH3 oxidation at high temperatures. The addition of ceria mitigated the undesirable migration of Pt between the LNT and SCR layers. Hydrothermal aging had a smaller effect on dual-layer catalysts containing ceria.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Dual layer SCR (top)/LNT (bottom) monolithic catalysts synthesized for lean NOx reduction. ► Rich-lean period switching generates NH3 in LNT layer and reduces NOx in SCR layer. ► Dual-layer catalysts achieve higher N2 selectivity than LNT-only catalyst at same NOx conversion. ► Dual-layer catalyst has higher NOx conversion than LNT-only catalyst in presence of CO2 and H2O. ► Ceria improves NOx reduction below 250 °C and mitigates PGM migration.

Keywords
Dual-layer catalyst; Monolith; Lean NOx Trap; NOx storage and reduction; Selective catalytic reduction; Ceria; Cu; Fe; ZSM-5; NH3; Lean NOx reduction; Pt
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Coupled NOx storage and reduction and selective catalytic reduction using dual-layer monolithic catalysts
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Publisher
Database: Elsevier - ScienceDirect
Journal: Applied Catalysis B: Environmental - Volumes 121–122, 13 June 2012, Pages 239–251
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Catalysis
Get Full-Text Now
Don't Miss Today's Special Offer
Price was $35.95
You save - $31
Price after discount Only $4.95
100% Money Back Guarantee
Full-text PDF Download
Online Support
Any Questions? feel free to contact us