Synthesis and characterization of nanostructured materials

The following thesis aims to address the constantly looming problem of indoor pollution. In fact, most of our time is spent in environments where the air exchange is not so sudden.This situation causes the accumulation of molecules harmful to our respiratory systems, leading to the onset of often lethal pathologies.Among the various abatement techniques, we focus on catalytic oxidation at low temperature.Manganese oxides are effective for abatement of substances such as volatile organic compounds.In the experimental part of the thesis, the different aspects related to the crystalline phases and catalytic properties of manganese oxides, mainly MnO_2 and 〖Mn〗_2 O_3 synthesized by Solution Combustion Synthesis (SCS) technique are, therefore, analysed and compared with the respective commercial ones.This technique is advantageous as it is simple and hasty and allows to obtain porous solids. Surface morphology, structure and chemical composition of the various samples are determined through characterization techniques XPS, XRD, H_2-TPR, O_2-TPD, FESEM and physisorption with nitrogen at -196°C.Through these techniques, it is possible to estimate the specific surface area, to determine the pore size distribution and the oxidation state of the surface state, to calculate and the dimension of crystallites.Furthermore, through the reduction and desorption at programmed temperature it is estimated the reducibility and of the sample. From the H2-TPR, MnO2 SCS shows to consume highest amount of hydrogen at low temperatures between 300-310°C with a total consumption of hydrogen equal to 11,7 mmol/gcat, meaning that the catalyst is more reducible.We move on to the actual testing phase in which we aim to determine the abatement capacity of samples.The gaseous current entering in the reactive system is composed by 100 ppm of pollutant, 21% of oxygen and nitrogen to balance. The molecules, used as pollutants, are ethylene, propylene, and carbon monoxide.The aim was to recreate the same condition of indoor air. After these experimental tests, comparing the results, MnO2 SCS is significantly better performing than the others. For CO, complete conversion is achieved already at 115°C, while for ethylene 225°C and propylene 175°C. For this reason, the more challenging studies are conducted just for MnO2 SCS: the analysis of stability and reproducibility, the study of the catalyst behaviour in presence of water. By performing the catalytic tests under wet conditions, it is seen a worsening of the MnO2 SCS conversion capacity, due to the adsorption of water on catalyst’s active sites. In this case, complete conversion for carbon monoxide is achieved at 200°C, 275°C for ethylene and 225°C for propylene. For all three molecules the conversion remained constant, demonstrating the stability of the sample.For the TOS in wet conditions, the same operational choices were maintained.The cyclic tests in dry condition involved a testing repeated three times. The conversion results are like each other, proving that the series of cycles did not damage the structure of the catalyst. Finally, reproducibility tests were conducted. They consisted of repeating the same conversion test in dry conditions by increasing the temperature linearly four times. The conversion curves overlap, demonstrating that similar results can be obtained. In conclusion we can state that MnO2 SCS is a high-performance catalyst, stable over time and the results obtained can be considered reproducible.