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The Effects of CO, H 2 , and C 3 H 6 on the SCR Reactions of an Fe Zeolite SCR Catalyst
ISSN: 0148-7191, e-ISSN: 2688-3627
Published April 08, 2013 by SAE International in United States
Annotation ability available
Selective Catalytic Reduction (SCR) catalysts used in Lean NOx Trap (LNT) - SCR exhaust aftertreatment systems typically encounter alternating oxidizing and reducing environments. Reducing conditions occur when diesel fuel is injected upstream of a reformer catalyst, generating high concentrations of hydrogen (H₂), carbon monoxide (CO), and hydrocarbons to deNOx the LNT. In this study, the functionality of an iron (Fe) zeolite SCR catalyst is explored with a bench top reactor during steady-state and cyclic transient SCR operation.
Experiments to characterize the effect of an LNT deNOx event on SCR operation show that adding H₂ or CO only slightly changes SCR behavior with the primary contribution being an enhancement of nitrogen dioxide (NO₂) decomposition into nitric oxide (NO). Exposure of the catalyst to C₃H₆ (a surrogate for an actual exhaust HC mixture) leads to a significant decrease in NOx reduction capabilities of the catalyst. A degradation mechanism is proposed to account for the decrease in NOx conversion efficiency, highlighted by reactions between NO₂ and C₃H₆ to make NO at a rate of similar order of magnitude as the Fast SCR reaction. This inhibits SCR reactions when the NO:NOx ratio favors NO, but can increase NOx conversion when the NO:NOx ratio favors NO₂.
Ammonia (NH₃) storage is only marginally affected by the presence of H₂, CO, or C₃H₆; but significant amounts of C₃H₆ can be stored on the catalyst. Further observation reveals that the oxidation effects of C₃H₆ are non-negligible and C₃H₆ strongly influences the oxidation of NH₃. The degradation mechanism includes seven proposed reactions to model the experimental results of adding H₂, CO, and C₃H₆ to the SCR feed gas during steady-state and transient operation.
CitationSmith, M., Depcik, C., Hoard, J., Bohac, S. et al., "The Effects of CO, H2, and C3H6 on the SCR Reactions of an Fe Zeolite SCR Catalyst," SAE Technical Paper 2013-01-1062, 2013, https://doi.org/10.4271/2013-01-1062.
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