Studio della chimica redox in zeoliti scamabiate rame tramite analisi avanzata di dati XAS ​

Air pollution is currently the most important environmental risk to human health, and it is perceived as the second biggest environmental concern for Europeans, after climate change according to the European Commission report of 2017.1 Among the air pollutants, nitrogen oxides (NOx) are known to hold a key role in in the number of premature deaths connected to respiratory, cardiovascular and cancer diseases. Moreover, NOx are also environmentally harmful contributing to the process of ozone, PM10 and photochemical smog formation while interacting with other pollutants.2 The production of NOx is primarily due to the combustion of fossil fuels by vehicles and various stationary sources, though they are by products of all combustion-based systems and of all high-temperature industrial processes. To mitigate these problems, since the 1970s, diesel engines and power plants begin to use the chemical process of selective catalytic reduction of NOx to N2 assisted by ammonia (NH3-SCR). The first family of catalysts employed for this process was based on vanadium oxides. Nowadays instead, the research has shifted towards metal-exchanged-zeolite catalysts. This type of catalysts provides outstanding performances, in terms of both activity and hydrothermal stability, especially for mobile deNOx applications in the automotive sector, when used in the after treatment systems for diesel vehicles.3–5 In this work, it will be presented an advanced X-ray absorption spectroscopy (XAS) study on a set of Cu-exchanged-zeolite samples, focusing on understanding the redox chemistry involving Cu ions hosted in the zeolite framework under in situ conditions relevant to the NH3-SCR reaction. In Chapter 1, it will be given a general overview on the XAS technique and the data analysis approaches utilized in this work. Successively, in Chapter 2 we will treat the structure and the key properties of the Cu-CHA catalyst and its redox-chemistry in the NH3 assisted SCR reaction, giving particular emphasis to previous XAS studies. From Chapter 3, we will begin the discussion of studied systems with the sections related to materials and methods. The qualitative interpretation of the XAS spectra and the discussion of the results obtained applying different data analysis approaches in both the X-ray absorption near edge spectroscopy (XANES) and the extended X-ray absorption fine structure (EXAFS) region, such as XANES linear combination fit (LCF), and EXAFS Wavelet Transform (WT) and fitting, described in Chapter 2, will be presented in Chapters 4,5. In Chapter 6, it will be then showed a XANES FDMNES simulation study aimed to further support our findings. Finally, a critical sum up and overview on the results will be given in the final chapter (Chapter 7).