Investigation of the effects of biodiesel-based Na on emissions control components
A single-cylinder diesel engine was used to investigate the impact of biodiesel-based Na on emissions control components using specially blended 20% biodiesel fuel (B20). The emissions control components investigated were a diesel oxidation catalyst (DOC), a Cu–zeolite-based NH3-SCR (selective catalytic reduction) catalyst, and a diesel particulate filter (DPF). Both light-duty vehicle, DOC–SCR–DPF, and heavy-duty vehicle, DOC–DPF–SCR, emissions control configurations were employed. The accelerated Na aging is achieved by introducing elevated Na levels in the fuel, to represent full useful life exposure, and periodically increasing the exhaust temperature to replicate DPF regeneration. To assess the validity of the implemented accelerated Na aging protocol, engine-aged lean NOx traps (LNTs), DOCs and DPFs are also evaluated. To fully characterize the impact on the catalytic activity the LNT, DOC and SCR catalysts were evaluated using a bench flow reactor. The evaluation of the aged DOC samples and LNT show little to no deactivation as a result of Na contamination. However, the SCR in the light-duty configuration (DOC–SCR–DPF) was severely affected by Na contamination, especially when NO was the only fed NOx source. In the heavy-duty configuration (DOC–DPF–SCR), no impact is observed in the SCR NOx reduction activity. Electron probe micro-analysis (EPMA) reveals that Na contamination on the LNT, DOC, and SCR samples is present throughout the length of the catalysts with a higher concentration on the washcoat surface. In both the long-term engine-aged DPF and the accelerated Na-aged DPFs, there is significant Na ash present in the upstream channels; however, in the engine-aged sample lube oil-based ash is the predominant constituent.
Graphical abstractFigure optionsDownload full-size imageDownload high-quality image (202 K)Download as PowerPoint slideHighlights► SCR catalysts are most susceptible to performance losses as a result of Na contamination. ► Flowing equimolar NO2 + NO results in minimal deactivation of the SCR catalyst. ► Placing the SCR behind the DPF can protect the zeolite from Na contamination. ► Cordierite DPFs are susceptible to Na penetration into the physical walls.
Journal: Catalysis Today - Volume 184, Issue 1, 30 April 2012, Pages 205–218