Doped ceria nanostructures for the oxidation of pollutants: investigations into the role of defect sites
Year: 2021
Type: dissertation
Abstract: Air pollution is a worldwide phenomenon strictly connected to severe risks to human health.Among the anthropic activities linked to the production of noxious compounds, road transport is one of the most impacting, especially in highly populated urban areas.In order to preserve air quality and the environment, strict regulations in terms of emission limits have been adopted by several nations.As a consequence, most vehicles are today equipped with a complex aftertreatment line in which the pollutants can be converted into harmless substances.To this end, oxidation catalysts are needed to convert CO and unburned hydrocarbons into CO2; moreover, proper catalysts can also be deposited inside particulate filters to promote soot oxidation at lower temperature, reducing the fuel consumption and thermal shock during regeneration.Among the attractive alternatives to expensive noble metals, ceria-based materials have exhibited promising oxidative performances.Ceria activity is linked to its unique redox behavior and oxygen storage capacity, but several other factors, such as morphology, reducibility or defectiveness, concur in determining the final catalytic properties.All these features can be tuned by adjusting the synthesis conditions or by doping.In this thesis, different ceria-based nanostructured catalysts have been examined, with the intent of shedding light on the relevant structural and physicochemical properties defining the catalytic activity and on the reaction pathways involved.The materials, prepared via hydrothermal synthesis, were extensively characterized and tested following the procedures reported in Chapter 2.A first set of catalysts was obtained by doping ceria with Cu and Mn.The defect sites formed in ceria structure upon doping were investigated via in situ Raman spectroscopy, monitoring their behavior throughout thermal cycles and during soot oxidation (Chapter 3) and CO oxidation (Chapter 4).Three different types of structural defects were recognized, namely oxygen vacancies, Frenkel interstitial-vacancy pairs and vacancy-free substitutional sites.The defectiveness was correlated with catalytic activity towards CO oxidation, while an increase of vacancy-free sites after soot oxidation suggested that peroxides and superoxides First of all, I would like to thank very much prof.Samir Bensaid and prof.Marco Piumetti for guiding my work during the last three years with their invaluable expertise.I would also like to acknowledge prof.Fabrizio Giorgis, prof.Nunzio Russo and prof.Debora Fino for supervising my activities and contributing to the scientific discussions.A heartfelt thanks goes to Dr. Chiara Novara, for introducing me to Raman spectroscopy and for always being at my side during long experiments, data analysis and interpretation, paper writing, and so on.Thank you for having been not only an expert guide
Source: PORTO@Iris
Author: SARTORETTI, ENRICO
Language: English
Subfield: Materials Chemistry
Field: Materials Science
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7219230327