The present thesis work is based on the study of the effects of temperature, of the presence of CO2 and water in the reaction environment and of the type of reducing agents employed, over the performances of model and commercial LNT catalysts. A particular attention is given to the formation of N2O and to the selectivity towards the various reduction products. The experiments had been carried out in a laboratory rig and the outputs of the gaseous phase had been collected by means of a FT-IR analyser, a mass spectroscope and a µgas-chromatograph. In the first part of this work, three model catalysts (Pt-Ba/Al2O3, Rh-Ba/Al2O3 and PtRh-Ba/Al2O3) have been tested at three different temperatures (150°C, 250°C, 350°C). The Pt-Ba catalyst has been subject to experiments with and without CO2 and water in the reaction environment, using CO, H2 and propylene (in some of the tests) as reducing agents; the others have been tested only in presence of CO2 and water, with all the three reductants. All the catalysts showed an increase of activity associated with the growth of the temperature, while the trend of N2O production appeared to be opposite. The presence of CO2 seemed not to have a strong impact on the performances of the catalysts, while water influenced in a larger extent their behaviour, especially at 350°C and in presence of propylene. From the results obtained, it is deduced that propylene decreases the reducing efficiency of the mixture at low temperature, while at 350°C the outcomes had been similar to the one registered in absence of the HC. Among the model catalysts, Pt-Ba and the bimetallic showed the best performances, while Rh-Ba presented a lower storage capacity also at high temperature. The second part is focused on the experiments carried over the commercial catalyst, as powder and as monolith, in presence of CO2 and water, with all the reductants employed. The catalyst had also been tested in the presence of soot and after a thermal treatment performed in presence of oxygen at high temperature (750°C). This last treatment seems to increase the storing and reducing properties of the catalyst, while soot does not seem to modify these abilities.
Il presente lavoro di tesi è basato sullo studio degli effetti di temperatura, presenza di CO2 e acqua e del tipo di agenti riducenti impiegati, sulle prestazioni di catalizzatori LNT modello e commerciale. Particolare attenzione è stata dedicata alla formazione di N2O e alla selettività verso i diversi prodotti di riduzione. Gli esperimenti sono stati condotti su un impianto di laboratorio e i risultati della fase gas sono stati ottenuti per mezzo di un analizzatore FT-IR, di uno spettrometro di massa e di un micro-gascromatografo. Nella prima parte, tre catalizzatori modello sono stati testati (Pt-Ba/Al2O3, Rh-Ba/Al2O3 e PtRh-Ba/Al2O3) a tre differenti temperature (150°C, 250°C, 350°C). Il catalizzatore Pt-Ba è stato sottoposto a prove in assenza e in presenza di CO2 e acqua, adoperando CO, H2 e in alcune prove propilene come agenti riducenti; i restanti sono stati testati esclusivamente in presenza di CO2 e acqua, con i tre riducenti. Un incremento dell’attività è stato notato a seguito dell’aumento della temperatura, mentre la produzione di N2O è risultata avere un andamento opposto. La presenza di CO2 nell’ambiente di reazione non ha avuto un impatto significativo sulle prestazioni dei catalizzatori, mentre l’acqua ha influenzato il comportamento degli stessi, in particolare a 350°C e in presenza di propilene. Dai risultati ottenuti è stato possibile dedurre che l’utilizzo di propilene limita le proprietà riducenti della miscela a basse temperature, mentre a 350°C le prestazioni sono apparse equiparabili. Tra i catalizzatori modello, il Pt-Ba e il bimetallico hanno mostrato il miglior funzionamento, mentre il Rh-Ba ha presentato scarse proprietà di accumulo anche ad alte temperature. La seconda parte è incentrata sugli esperimenti condotti su un catalizzatore commerciale, nella forma di polvere e di monolita, in presenza di CO2 e acqua, con i tre riducenti. Esso è stato poi testato in presenza di soot e a seguito di un trattamento termico in ossigeno ad alta temperatura (750°C). In particolare, quest’ultimo trattamento sembra incrementare attività e capacità di accumulo del catalizzatore, mentre il soot non sembra intaccare particolarmente tali abilità.
Study on N2O formation over LNT catalysts : effect of operating conditions
PALESE, ALESSANDRO;RUSSO, STEFANO
2017/2018
Abstract
The present thesis work is based on the study of the effects of temperature, of the presence of CO2 and water in the reaction environment and of the type of reducing agents employed, over the performances of model and commercial LNT catalysts. A particular attention is given to the formation of N2O and to the selectivity towards the various reduction products. The experiments had been carried out in a laboratory rig and the outputs of the gaseous phase had been collected by means of a FT-IR analyser, a mass spectroscope and a µgas-chromatograph. In the first part of this work, three model catalysts (Pt-Ba/Al2O3, Rh-Ba/Al2O3 and PtRh-Ba/Al2O3) have been tested at three different temperatures (150°C, 250°C, 350°C). The Pt-Ba catalyst has been subject to experiments with and without CO2 and water in the reaction environment, using CO, H2 and propylene (in some of the tests) as reducing agents; the others have been tested only in presence of CO2 and water, with all the three reductants. All the catalysts showed an increase of activity associated with the growth of the temperature, while the trend of N2O production appeared to be opposite. The presence of CO2 seemed not to have a strong impact on the performances of the catalysts, while water influenced in a larger extent their behaviour, especially at 350°C and in presence of propylene. From the results obtained, it is deduced that propylene decreases the reducing efficiency of the mixture at low temperature, while at 350°C the outcomes had been similar to the one registered in absence of the HC. Among the model catalysts, Pt-Ba and the bimetallic showed the best performances, while Rh-Ba presented a lower storage capacity also at high temperature. The second part is focused on the experiments carried over the commercial catalyst, as powder and as monolith, in presence of CO2 and water, with all the reductants employed. The catalyst had also been tested in the presence of soot and after a thermal treatment performed in presence of oxygen at high temperature (750°C). This last treatment seems to increase the storing and reducing properties of the catalyst, while soot does not seem to modify these abilities.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/145113