Catalytic elimination potential and kinetic model of urea and its by-products on V2O5-WO3/TiO2 catalyst

Besides catalyzing NOx reduction, the V 2 O 5 -WO 3 /TiO 2 catalyst can effectively suppress the formation of urea (CH 4 N 2 O) decomposition by-products in selective catalytic reduction (SCR). However, current research lacks a clear understanding of the impact of urea and its by-products on the catalyst' performance. Additionally, there is no available kinetic model to describe the decomposition process of urea and its by-products on the V 2 O 5 -WO 3 /TiO 2 catalyst. In this paper, the decomposition process of urea and its by-products on the catalyst was firstly investigated via thermogravimetric analysis (TGA). It was found that increasing the catalyst dosage can accelerate urea decomposition and block the transformation pathways from urea and biuret (C 2 H 5 N 3 O 2 ) to cyanuric acid (cya, C 3 H 3 N 3 O 3 ). However, as the decomposition temperature of the by-products increased, a larger amount of catalyst was also required. Secondly, the impact of urea and its by-products on the NOx reduction performance was investigated via the SCR test bench. The results showed that, at 200 ℃, the addition of 20 % urea, biuret, or cya decreased the NOx reduction rate by 7.2 %, 9.8 %, and 11.0 % respectively. Furthermore, the catalyst's performance was significantly improved at 400 ℃ dues to the decomposition of urea and its by-products. Then, various characterization techniques were used to analyze the morphology and chemical composition of the urea decomposition products on the catalyst at different temperatures. On this basis, a simplified urea non-catalytic and catalytic coupling mechanism model was developed, which included 7 species and 16 reactions. Finally, the kinetic parameters of the proposed urea catalytic decomposition model were optimized utilizing TGA test data, density functional theory (DFT), and genetic algorithms (GA). This study can provide guidance for the elimination of SCR urea deposits in engineering applications.