Relation between partial propene oxidation, sulphate content and selective catalytic reduction of NOx by propene on ceria/sulphated titania

The propene catalytic oxidation and the selective catalytic reduction of NO by propene (C3H6-SCR) have been studied over ceria catalysts supported on sulphated titania (ceria content of 0.9, 0.5, 0.3 and 0.04 wt%). XPS analysis and Raman spectroscopy were carried out in order to obtain information on ceria (oxidation degree, surface content, and particle size) and sulphate compounds (species and surface content). The NOx reactivity was mainly linked to the sulphate content. The higher the sulphate content, the higher the NOx reactivity. The partial C3H6 oxidation has a role in the NOx activity. The lower the partial C3H6 oxidation into CO, the better the NOx reactivity. However, N2 selectivity was higher for the sample with the lowest sulphate content (i.e. the highest partial C3H6 oxidation). Sulphate compounds like SO32− and/or SO42− with reduced ceria (Ce3+) activate the C3H6 and NO compounds. Moreover, in the range of ceria content studied here, with or without NO in the gas stream, C3H6 oxidation was also related to sulphate content and not to ceria content. Nevertheless, the presence of ceria provides oxygen for NO oxidation to form nitrate, oxygen coming from Ce3+Vo species at the surface (Vo: oxygen vacancy). The key parameter between NOx reduction and N2 selectivity was observed to be the sulphate content.