Atmospheric pollution is nowadays one of the main concerns that automotive industry is facing, for this reason research on aftertreatment technologies is a flourishing field. Several catalytic systems have been developed in order to mitigate engines emissions. In this thesis, different technologies for the treatment and abatement of NOx have been considered and analyzed: Passive NOx Adsorber (PNA), Diesel Oxidation Catalyst (DOC) and Selective Catalytic Reduction (SCR) catalyst. The researches have been performed at Paul Scherrer Institute (PSI) in Switzerland and at Politecnico di Milano (Bovisa). PNAs are zeolite-based catalysts using noble metals and metal oxides as active phase. They have been developed in order to meet the Diesel NOx emission regulation. These systems are able to adsorb NOx at low temperature and release them at SCR activity temperature. First, PNA catalytic experiments were focused on testing alternative metals as active phases with respect to Pd (considered in literature as the best active phase for this catalytic system). Then, has been developed a focus study on the behavior of Pd-based catalyst during NO adsorption and desorption. The results show that none of the Me-based catalysts tested have an adsorption capacity comparable with Pd-based catalyst. DOCs are catalyst using a coated high surface area as substrate and precious metals such Pd and Pt as active phase. They act oxidizing several pollutants coming from the combustion chamber such as CO into CO2, and part of NO into NO2. The latter conversion enhances the further SCR abetment step. The studies about DOC focused on thermal aging and chemical poisoning of a model Pd/Al2O3 catalyst. First, the thermal effect was analyzed for different aging temperatures, then the effects of two different poisons (phosphorus and sulfur) were tested. The main conclusions of this study are: bigger particles enhance the oxidation activity, thermal aging sinters platinum and increases conversion, phosphorous poisoning forms aluminum phosphates that cause deactivation, sulfur poisoning (reversible poisoning) inhibits the reaction. SCR systems are catalysts formed by a substrate of zeolites or titania with active phases such as Cu or Vanadium oxides respectively. They are used to reduce NOx into N2 trough a reductant species as NH3. SCR tests were performed with vanadium-tungsten-titanium (VWT) and vanadium-titanium-based catalysts (VT). The goal of the experiments was to understand the effects of the promoter tungsta (WO3) on the V2O5/TiO2 (active phase/substrate) catalyst. Activity tests clearly show the promoting effect of tungsta. Furthermore, tungsta affects the acid sites ratio increasing the amount of Bronsted acid sites with respect to Lewis acid sites.
L'inquinamento atmosferico è oggi una delle principali preoccupazioni che l'industria automobilistica sta affrontando, per questo motivo è molto fiorente la ricerca sulle tecnologie di post-trattamento. Diversi sistemi catalitici sono stati sviluppati per mitigare le emissioni dei motori. In questa tesi sono state studiate differenti tecnologie per il trattamento e l'abbattimento di NOx: passive NOx Adsorber (PNA), Diesel Oxidation Catalyst (DOC) e catalizzatore selettivo di riduzione catalitica (SCR). Le ricerche sono state svolte al Paul Scherrer Institut (PSI) in Svizzera ed al Politecnico di Milano (Bovisa). I sistemi PNA sono catalizzatori che usano come substrato le zeoliti e come fase attiva i metalli nobili e gli ossidi metallici. Sono stati creati per riuscire a raggiungere i nuovi standard di emissione di NOx. Questi sistemi sono infatti in grado di adsorbire gli NOx a bassa temperatura e di rilasciarli alla temperatura a cui i sistemi SCR sono attivi. Inizialmente gli esperimenti catalitici sul PNA si sono concentrati su diverse fasi attive metalliche alternative al Pd (considerato in letteratura come la migliore fase attiva per questi sistemi). Quindi, è stato svolto uno studio specifico sul comportamento del catalizzatore a base palladio durante l’adsorbimento ed il desorbimento di NO. I risultati mostrano che nessuno dei catalizzatori basati su metalli testati ha una capacità di adsorbimento paragonabile al catalizzatore al palladio. I sistemi DOC sono catalizzatori con substrato ad alta area superficiale e sottoposta a coating su cui viene posta come fase attiva il Pd ed il Pt. Questi catalizzatori ossidano diversi inquinanti proveniente dalla camera di combustione come il CO in CO2 e parte dell’NO in NO2. Quest’ultimo migliora l’efficienza del successivo stadio di abbattimento SCR. Gli studi sul DOC si sono concentrati sull'invecchiamento termico e l'avvelenamento chimico di un catalizzatore Pd/Al2O3. Per primo è stato analizzato l'effetto termico per le diverse temperature di invecchiamento, poi sono stati testati gli effetti di due diversi veleni (fosforo e zolfo). Le principali conclusioni di questo studio sono state: le particelle più grandi migliorano la conversione (ossidazione), l'invecchiamento termico sinterizza il platino e aumenta la conversione l'avvelenamento da fosforo forma fosfati di alluminio che causano la disattivazione, l'avvelenamento da zolfo (risultato reversibile) inibisce la reazione. I sistemi SCR sono catalizzatori formati da un substrato di zeoliti o di titania e utilizzano come fase attiva Cu o vanadio rispettivamente. Sono usati per ridurre gli NOx in N2 attraverso una specie riducente come l’NH3. I test SCR sono stati eseguiti con vanadio-tungsteno-titanio (VWT) e catalizzatore a base di vanadio-titanio (VT). L'obiettivo degli esperimenti era comprendere gli effetti del promotore tungsta (WO3) sul catalizzatore V2O5/ TiO2 (fase attiva / substrato). I test di attività mostrano chiaramente l'effetto promotore della tungsta. Inoltre essa influenza il rapporto dei siti acidi, aumentando la quantità di siti acidi di Brønsted rispetto ai siti acidi di Lewis.
Investigation on emission control technologies for automotive applications
ORTINO GHINI, LORENZO;COFFANO, CHIARA
2018/2019
Abstract
Atmospheric pollution is nowadays one of the main concerns that automotive industry is facing, for this reason research on aftertreatment technologies is a flourishing field. Several catalytic systems have been developed in order to mitigate engines emissions. In this thesis, different technologies for the treatment and abatement of NOx have been considered and analyzed: Passive NOx Adsorber (PNA), Diesel Oxidation Catalyst (DOC) and Selective Catalytic Reduction (SCR) catalyst. The researches have been performed at Paul Scherrer Institute (PSI) in Switzerland and at Politecnico di Milano (Bovisa). PNAs are zeolite-based catalysts using noble metals and metal oxides as active phase. They have been developed in order to meet the Diesel NOx emission regulation. These systems are able to adsorb NOx at low temperature and release them at SCR activity temperature. First, PNA catalytic experiments were focused on testing alternative metals as active phases with respect to Pd (considered in literature as the best active phase for this catalytic system). Then, has been developed a focus study on the behavior of Pd-based catalyst during NO adsorption and desorption. The results show that none of the Me-based catalysts tested have an adsorption capacity comparable with Pd-based catalyst. DOCs are catalyst using a coated high surface area as substrate and precious metals such Pd and Pt as active phase. They act oxidizing several pollutants coming from the combustion chamber such as CO into CO2, and part of NO into NO2. The latter conversion enhances the further SCR abetment step. The studies about DOC focused on thermal aging and chemical poisoning of a model Pd/Al2O3 catalyst. First, the thermal effect was analyzed for different aging temperatures, then the effects of two different poisons (phosphorus and sulfur) were tested. The main conclusions of this study are: bigger particles enhance the oxidation activity, thermal aging sinters platinum and increases conversion, phosphorous poisoning forms aluminum phosphates that cause deactivation, sulfur poisoning (reversible poisoning) inhibits the reaction. SCR systems are catalysts formed by a substrate of zeolites or titania with active phases such as Cu or Vanadium oxides respectively. They are used to reduce NOx into N2 trough a reductant species as NH3. SCR tests were performed with vanadium-tungsten-titanium (VWT) and vanadium-titanium-based catalysts (VT). The goal of the experiments was to understand the effects of the promoter tungsta (WO3) on the V2O5/TiO2 (active phase/substrate) catalyst. Activity tests clearly show the promoting effect of tungsta. Furthermore, tungsta affects the acid sites ratio increasing the amount of Bronsted acid sites with respect to Lewis acid sites.File | Dimensione | Formato | |
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https://hdl.handle.net/10589/150150