Titania supported vanadium oxide catalysts in the NH3-SCR reaction: Effect of vanadium loading, promoters and aging

Licentiate thesis, 2023

Emissions of nitrogen oxides (NOx) from combustion processes in mobile sources attract significant attention due to their role as a major source of atmospheric contamination, along with health risks and environmental issues. Since combustion processes in heavy-duty vehicles are expected to be used for a foreseeable future, many efforts have been invested in a suitable deNOx technology. The selective catalytic reduction with ammonia (NH3-SCR) over vanadium-based catalysts is one of the most established technologies to control NOx emissions due to their various benefits. However, the application in mobile sources cause several challenges, as the catalyst has to work under dynamic conditions in a broad temperature window. Promising solutions have emerged with the implementation of promoters to the active vanadium phase.

The rational design for innovative V-based catalysts requires an improved fundamental understanding of the functions and interactions between the included components that affect the catalysts properties. In this work, the effect of the vanadium loading and the implementation of two promoters (Ce, Nb) were investigated. As in automotive applications the thermal deactivation is a challenge, a special focus was set on the aging impact. The results showed that a high vanadium loading favours the low-temperature activity while thermal stability is achieved with a low vanadium loading. The implementation of Ce results in an improved low-temperature activity, while the incorporation of Nb contributes to a higher thermal stability. Infrared spectroscopic methods such as Raman and in situ DRIFTS allowed the identification of surface vanadium oxide species and band assignments for the surface hydroxyl groups and adsorbed surface species of the reactants (NH3, NO). The deconvolution of the NOx adsorption spectra enabled a comparison of the surface species ratio among the samples.