NOx emissions from diesel vehicles are efficiently reduced in warm engine conditions by ammonia/urea over NH3-SCR catalysts (e.g. Cu- or Fe- exchanged zeolites). On the contrary, the amount of NOx released in the atmosphere is significantly higher during the cold start phase. Indeed, during this transient: i) the inability of decomposing urea prevents from fully exploiting the SCR technology; ii) Cu- and even more Fe- zeolites have a poor deNOx activity. Moreover, a complete fundamental understanding of the Standard SCR reaction (4 NO + 4 NH3 + O2 → 4 N2 + 6 H2O), which is crucial for the formulation of high performance catalysts and for the development of numerical models, is still lacking. My Ph.D. thesis is focused on the low temperature challenges of deNOx aftertreatment systems, and aims at elucidating the mechanistic aspects of the Standard SCR reaction and at developing industrially relevant and practical solutions for NOx emission control.
Le emissioni di NOx dei veicoli diesel sono efficacemente ridotte ad alta temperatura (T>200°C) con la tecnologia NH3-SCR utilizzando come catalizzatori Fe/Cu-zeoliti. Nonostante ciò, durante la fase di avviamento a freddo la quantità di NOx rilasciata nell'atmosfera è ancora rilevante. Infatti, in questo transitorio: i) l'urea non si decompone, impedendo di sfruttare appieno i sistemi di post-trattamento basati sull’ NH3-SCR; ii) i catalizzatori SCR hanno una scarsa attività di deNOx. Inoltre, il meccanismo della reazione standard SCR (4 NO + 4 NH3 + O2 → 4 N2 + 6 H2O) non è ben definito. La mia tesi di dottorato è focalizzata su queste problematiche, mirando a chiarire alcuni aspetti fondamentali della reazione Standard SCR e a sviluppare soluzioni rilevanti dal punto di vista industriale per il controllo delle emissioni di NOx.
Low temperature issues of SCR systems: from fundamental understanding of the standard SCR reaction mechanism to practical applications for cold start emissions control
GRAMIGNI, FEDERICA
2019/2020
Abstract
NOx emissions from diesel vehicles are efficiently reduced in warm engine conditions by ammonia/urea over NH3-SCR catalysts (e.g. Cu- or Fe- exchanged zeolites). On the contrary, the amount of NOx released in the atmosphere is significantly higher during the cold start phase. Indeed, during this transient: i) the inability of decomposing urea prevents from fully exploiting the SCR technology; ii) Cu- and even more Fe- zeolites have a poor deNOx activity. Moreover, a complete fundamental understanding of the Standard SCR reaction (4 NO + 4 NH3 + O2 → 4 N2 + 6 H2O), which is crucial for the formulation of high performance catalysts and for the development of numerical models, is still lacking. My Ph.D. thesis is focused on the low temperature challenges of deNOx aftertreatment systems, and aims at elucidating the mechanistic aspects of the Standard SCR reaction and at developing industrially relevant and practical solutions for NOx emission control.File | Dimensione | Formato | |
---|---|---|---|
2020_06_Gramigni.pdf
non accessibile
Descrizione: Testo della tesi
Dimensione
38.45 MB
Formato
Adobe PDF
|
38.45 MB | Adobe PDF | Visualizza/Apri |
I documenti in POLITesi sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
https://hdl.handle.net/10589/166682