Understanding urea decomposition is critical to achieve highly efficient selective catalytic reduction (SCR). The urea decomposition process in an exhaust pipe and in Cu‐zeolite and vanadia‐SCR (V‐SCR) was studied in engine test cells. The unconverted urea at the SCR inlet can be substantial at lower temperatures. HNCO and NH₃ are two dominant products at the SCR inlet. Urea and HNCO continue to decompose in SCR catalysts, with a rate much faster than in the homogeneous stream. The HNCO hydrolysis process is extremely efficient in Cu‐zeolite SCR and the abundant NH₃ from urea overdosing can improve the NO_x conversion efficiency. While for V‐SCR, the HNCO hydrolysis reaction can become the rate‐limiting step (especially after aging), abundant urea at low temperatures impairs NO_x reduction.

中文翻译：

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铜沸石和钒选择性催化还原的尿素分解及其对NOx还原的意义

了解尿素的分解对于实现高效的选择性催化还原（SCR）至关重要。在发动机测试室中研究了排气管，Cu沸石和vanadiaSCR（VSCR）中尿素的分解过程。在较低的温度下，SCR入口处未转化的尿素可能会很大。HNCO和NH ₃是SCR入口处的两个主要产物。尿素和HNCO在SCR催化剂中继续分解，其分解速度比在均相流中快得多。HNCO水解过程在Cu-沸石SCR中非常有效，过量添加尿素产生的大量NH ₃可改善NO _x转换效率。而对于V-可控硅，HNCO水解反应可成为在低温下也妨碍NO的限速步骤（特别是在老化之后），丰富的尿素_X还原。