Sulphated TiO2 for selective catalytic reduction of NOx by n-decane

The selective catalytic reduction of NO by n-decane (C10H22-SCR), with or without water (1.5 vol.%), has been studied over sulphated titania catalysts (∼2 wt% S). Such sulphated materials have been explored as candidates for HC-SCR by decane with process temperatures >600 °C. The nature of the functional groups from residual reaction products and the thermal stability of sulphated compounds were characterized by mass spectroscopy, FTIR analysis and temperature programmed desorption experiments. It was observed that hydrocarbons (CxHy), aldehyde (RCHO), acid (RCOOH), ester (RCOOR) and primary and secondary amine (RNH2, R2NH) functional groups were present at the catalyst surface. For the sample not tested under HC-SCR reaction, the sulphate compounds (SO42−, SO32−) were stable up to 600 °C under He-TPD whereas for samples tested under the HC-SCR reaction, sulphate species were released above 400 °C. This might be due to the exothermic oxidation reaction of deposited carbon compounds, characterized by ex situ analysis, with oxygen supplied by the sulphated support. This effect was confirmed by mixing the catalyst with soot particles. Lastly, we propose a reaction scheme for the HC-SCR of NO by decane over sulphated titania.