Abstract:

When the urea-selective catalytic reduction technology runs at low temperatures, urea is not completely decomposed, and it is easy to form by-products such as biuret, cyanuric acid and melamine. In this study, TiO₂ catalyst was combined with dielectric barrier discharge plasma for hydrolysis of urea decomposition by-products with or without O₂ in the carrier gas under temperature-programmed conditions. Experimental results show that biuret, cyanuric acid and melamine over TiO₂ could be hydrolyzed to NH₃ and CO₂ at 43—261℃, 217—300℃ and 199—300℃, respectively. The presence or absence of O₂ in the carrier gas hardly affects the catalytic hydrolysis process. Introducing plasma significantly decreases the hydrolysis temperatures of biuret, cyanuric acid and melamine. Insignificant variation of NH₃ yield and small amounts of N₂O and NO by-products are observed when plasma is applied in the O₂-free carrier gas. In the O₂-containing case, NH₃ yield obviously decreases while more N₂O, NO, NO₂ and small amounts of NH₄NO₂ and NH₄NO₃ are generated by applying plasma. To overcome drawbacks of the plasma-enhanced process, mainly the formation of by-products, further work is required in the future, such as optimizing discharge conditions and catalyst compositions.

Key words: urea decomposition by-products, non-thermal plasma, catalysis, hydrolysis, SCR

摘要：

尿素-选择性催化还原技术低温下运行时尿素分解不彻底，易形成缩二脲、三聚氰酸和三聚氰胺等副产物。本研究将TiO₂催化剂与介质阻挡放电等离子体相结合，在程序升温条件下考察了载气中有无O₂时引入等离子体前后TiO₂催化尿素分解副产物水解的性能。结果表明：TiO₂表面缩二脲、三聚氰酸和三聚氰胺分别在43~261℃、217~300℃和199~300℃水解生成NH₃和CO₂，载气中有无O₂对催化水解过程几乎无影响。引入等离子体后缩二脲、三聚氰酸和三聚氰胺水解所需温度显著降低，载气中无O₂时引入等离子体NH₃产率变化不大，副产物仅有少量N₂O和NO，有O₂时NH₃产率显著降低，且生成较多N₂O、NO、NO₂及少量NH₄NO₂和NH₄NO₃。未来需从优化放电条件和催化剂组成等方面解决引入等离子体导致副产物形成等问题。

关键词: 尿素分解副产物, 非热等离子体, 催化, 水解, 选择性催化还原