CO2 concentration into the atmosphere is mainly due to emissions from fossil fuel-based power plants and other industrial activities. The increasing awareness of climate change has led to intense research efforts to develop effective processes for lowering pollutant emissions. CO2 abatement strategy, based on combined CO2 capture and methanation, can turn waste CO2 into valuable products. Production of methane from captured CO2 and renewable H2 represents a promising route for the chemical storage of excess renewable energy. The technical challenge of carbon capture and storage (CCS) is related to the development of materials with high CO2 adsorption capacity, CH4 selectivity and thermal stability. In this field, DFM is a new, attractive alternative that consists of a storage component, an alkaline/alkaline earth metal, and a methanation active element, dispersed on a high surface support. Lately, Ru-based systems have been preferred to traditional Ni-based catalysts since they are active at lower temperature and allow a higher per-pass CO2 conversion with almost complete selectivity to CH4. The mechanism of CO2 methanation is complex and object of intense research activity. In this thesis work, an experimental approach is followed to investigate the Sabatier reaction, monitoring reactor outlet gas phase by means of GC analysis, FT-IR and mass spectroscopy. To this aim, four catalytic systems are analysed: Ru/Al2O3, Ba/Al2O3, Ru-Ba/Al2O3, Ru/Al2O3+Ba/Al2O3. The performed tests are: TPR to probe the reactivity of the system; TPD to investigate the maximum CO2 adsorption; TPSR to evaluate the reactivity of adsorbed species. To elucidate the influence of reacting environment, cyclic tests in different simulated flue gas conditions are carried out. The obtained results, in clean conditions, reveal a not marked beneficial effect on CO2 hydrogenation of the proximity between adsorbent and reducing elements; probably due to a predominant thermal effect on CO2 desorption. At variance, in presence of pollutants (i.e. NOx), a controlling role of Ru-Ba neighbouring couples is gathered, probably because Ru affects the catalytic surface regeneration.
La concentrazione di CO2 in atmosfera è dovuta principalmente alle emissioni da impianti di potenza basati su fonti fossili e da altre attività industriali. La crescente consapevolezza del cambiamento climatico in atto ha alimentato un’intensa attività di ricerca per sviluppare processi efficaci nel ridurre le emissioni. La strategia di abbattimento della CO2, basata sulla sua cattura e metanazione, converte la CO2 in prodotti di valore. La produzione di CH4 da CO2 e dall’H2, da fonti rinnovabili, è soluzione promettente per l’immagazzinamento chimico dell’energia rinnovabile in eccesso. La sfida tecnica inerente alla cattura e stoccaggio del carbonio (CCS) è legata allo sviluppo di materiali con alta capacità di adsorbimento, selettività a CH4 e stabilità termica. In quest’ambito, il DFM è una nuova ed attraente alternativa che prevede un componente adsorbente ed uno attivo nella metanazione, dispersi su un supporto ad alta area superficiale. Ultimamente, sistemi basati sul Ru sono preferiti a quelli tradizionali a base di Ni dato che sono attivi a temperature più basse e permettono una maggiore conversione di CO2 per passaggio con quasi completa selettività a CH4. Il complesso meccanismo della metanazione è oggetto di ricerca. Nel lavoro di tesi, è adottato un approccio sperimentale per investigare la reazione di Sabatier, monitorando la fase gas con analisi al GC, spettrometro di massa e infrarosso. Quattro sistemi catalitici sono analizzati: Ru/Al2O3, Ba/Al2O3, Ru-Ba/Al2O3, Ru/Al2O3+Ba/Al2O3. I test eseguiti sono: TPR per verificare la reattività del sistema; TPD per indagare il massimo adsorbimento di CO2; TPSR per valutare la reattività delle specie adsorbite. Per analizzare l’influenza dell’ambiente di reazione, sono condotti differenti test ciclici. I risultati ottenuti in condizioni “pulite” rivelano la mancanza di un marcato effetto benefico sull’idrogenazione della CO2 da parte della vicinanza di Ru e Ba; probabilmente a causa di un predominante effetto termico sul desorbimento della CO2. Al contrario, in presenza di inquinanti (NOx), la prossimità di Ru-Ba ha un ruolo determinante dato che il Ru influenza la rigenerazione della superficie catalitica.
Study of Ru-Ba supported catalysts for the methanation of CO2 in cyclic conditions
MOGNI, MARIALBA
2018/2019
Abstract
CO2 concentration into the atmosphere is mainly due to emissions from fossil fuel-based power plants and other industrial activities. The increasing awareness of climate change has led to intense research efforts to develop effective processes for lowering pollutant emissions. CO2 abatement strategy, based on combined CO2 capture and methanation, can turn waste CO2 into valuable products. Production of methane from captured CO2 and renewable H2 represents a promising route for the chemical storage of excess renewable energy. The technical challenge of carbon capture and storage (CCS) is related to the development of materials with high CO2 adsorption capacity, CH4 selectivity and thermal stability. In this field, DFM is a new, attractive alternative that consists of a storage component, an alkaline/alkaline earth metal, and a methanation active element, dispersed on a high surface support. Lately, Ru-based systems have been preferred to traditional Ni-based catalysts since they are active at lower temperature and allow a higher per-pass CO2 conversion with almost complete selectivity to CH4. The mechanism of CO2 methanation is complex and object of intense research activity. In this thesis work, an experimental approach is followed to investigate the Sabatier reaction, monitoring reactor outlet gas phase by means of GC analysis, FT-IR and mass spectroscopy. To this aim, four catalytic systems are analysed: Ru/Al2O3, Ba/Al2O3, Ru-Ba/Al2O3, Ru/Al2O3+Ba/Al2O3. The performed tests are: TPR to probe the reactivity of the system; TPD to investigate the maximum CO2 adsorption; TPSR to evaluate the reactivity of adsorbed species. To elucidate the influence of reacting environment, cyclic tests in different simulated flue gas conditions are carried out. The obtained results, in clean conditions, reveal a not marked beneficial effect on CO2 hydrogenation of the proximity between adsorbent and reducing elements; probably due to a predominant thermal effect on CO2 desorption. At variance, in presence of pollutants (i.e. NOx), a controlling role of Ru-Ba neighbouring couples is gathered, probably because Ru affects the catalytic surface regeneration.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/151852