Model NOx depolama malzemesi olan Fe-Ba/Al2O3 malzemesinin yapısal ve NOx alım özellikleri

The composition effect of iron on the nature of the nitrogen oxides species and nitrogen oxide storage properties of barium oxide supported alumina was investigated. Nitrate-loaded samples were further treated at elevated temperatures in order to monitor the thermally induced structural changes.For the as prepared samples, the surface distribution and the thermal stability of the deposited barium nitrates were found to depend strongly on the interaction with the iron containing domains and the support material. It was observed that deposited nitrates have different thermal stability in iron containing samples. Besides, XRD data revealed that barium aluminate formation at elevated temperatures was diminished to a certain extent in the presence of iron. Moreover, the presence of iron depressed the gamma to alfa phase transformation temperature of alumina.FTIR experiments revealed that nitrogen dioxide adsorption at 323 K leads to the formation of nitrites for all of the samples at the initial introduction. In addition, iron containing samples indicate nitrosyl formation as well. With further doses, nitrite bands were converted into nitrate signals. Nitrogen dioxide adsorption on the samples containing Fe resulted in the accentuation of the surface/bidentate nitrates. Temperature dependent FTIR experiments showed that bulk nitrates were thermally more stable than the surface nitrates. TPD profile for barium/alumina sample was also found to be in line with the FTIR results, indicating that the high-temperature decomposition of bulk nitrates were in the form of nitric oxide and oxygen while the surface nitrates decomposed at lower temperatures and mostly as nitrogen dioxide.