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Abstract: diesel emission fluid (DEF) soaking and urea deposits on selective catalytic reduction (SCR) catalysts are critical issues for real diesel engine NH₃-SCR systems. To investigate the impact of DEF soaking and urea deposits on SCR catalyst performance, fresh cu-zeolite catalyst samples were drilled from a full-size SCR catalyst. Those samples were impregnated with DEF solutions and subsequently hydrothermally treated to simulate DEF soaking and urea deposits on real SCR catalysts during diesel engine operations. Their SCR performance was then evaluated in a flow reactor with a four-step test protocol. Test results show that the DEF soaking leached some Cu from the SCR catalysts and slightly reduced their Cu loadings. The loss of Cu and associated metal sites on the catalysts weakened their catalytic oxidation abilities and caused lower NO/NH₃ oxidation and lower high-temperature N₂O selectivity. Lower Cu loading also made the catalysts less active to the decomposition of surface ammonium nitrates and decreased low-temperature N₂O selectivity. Cu loss during DEF impregnation released more acid sites on the surface of the catalysts and increased their acidities, and more NH₃ was able to be adsorbed and involved in SCR reactions at medium and high temperatures. Due to lower NH₃ oxidation and higher NH₃ storage, the DEF-impregnated SCR catalyst samples showed higher NO_x conversion above 400 °C compared with the non-soaked one. The negative impact of urea deposits during DEF impregnation was not clearly observed, because the high-temperature hydrothermal treatment helped to remove the urea deposits.

TDEF soaking and urea deposits on the SCR catalyst are critical issues in real diesel engine NH3-SCR systems. To investigate the impact of DEF soaking and urea deposits on the SCR catalyst performance, fresh Cu-zeolite catalyst samples were drilled from a full size SCR catalyst with a formulation of Cu-SAPO-34. Those samples were impregnated in DEF solutions and subsequently hydrothermally treated to simulate DEF soaking and urea deposits on real SCR catalysts during diesel engine operations. Their SCR performance was then evaluated in a flow reactor with a fourstep test protocol. Test results show that, the DEF soaking could leach some Cu out from the SCR catalysts and slightly reduced their Cu loadings. The loss of Cu and associated metal sites on the catalysts weakened their catalytic oxidation abilities and caused the lower NO/NH3 oxidation and lower high-temperature N2O selectivity. Lower Cu loading also made the catalysts less active to surface ammonium nitrates decomposition in low temperatures and decreased the low-temperature N2O selectivity. The Cu loss during DEF soaking released more acid sites on the catalysts' surface and increased the catalyst acidities, and more NH3 could be adsorbed and involved into SCR reactions in medium and high temperatures. Due to the lower NH3 oxidation and higher NH3 storage, those DEF soaked SCR catalyst samples showed higher NOx conversions above 400 oC, compared with the non-soaked one. The negative impact of urea deposits during DEF soaking was not clearly observed, because the high-temperature hydrothermal treatment helped remove the urea deposits. In general, this is a good paper. The results are interesting and meaningful.

尿素水溶液浸渍对柴油机NH₃-SCR后处理铜基分子筛催化剂性能的影响

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