Impact of biodiesel-based Na on the selective catalytic reduction of NO_x by NH₃ over Cu-zeolite catalysts

A single-cylinder diesel engine was used to investigate the impact of Na on Cu-zeolite SCR catalysts using 20 % bio- and petrol-diesel fuel blend (B20) with elevated levels of Na. The Na exposure was performed on light-duty (DOC-SCR-DPF) and heavy-duty (DOC-DPF-SCR) configurations of the diesel emissions control devices. The accelerated Na aging is achieved by exposing the system to elevated levels of Na that represent full useful life exposure (700,000 km) and periodically increasing the exhaust temperature to replicate DPF regeneration. After aging, the NO_x performance and relevant chemistry of the SCR catalysts were evaluated in a bench flow reactor. The SCR in the DOC-SCR-DPF configuration was found to be severely affected by Na contamination, especially when NO was the only NO_x species in the simulated exhaust gases. In the DOC-DPF-SCR configuration, no impact is observed in the SCR NO_x reduction activity. Electron microprobe analysis (EPMA) reveals that Na contamination on the SCR samples in the DOC-SCR-DPF configuration is present throughout the length of the catalysts.