Effect of SO2 on the soot oxidation activity of flame spray pyrolysis-made manganese oxide catalyst in gasoline model exhaust

This study deals with the effect of SO₂ on the soot oxidation activity of flame spray pyrolysis-prepared manganese oxide in gasoline model exhaust. The catalyst was exposed to 15 and 30 ppm SO₂ at 250 °C and was characterized by N₂ physisorption, SO₂-TPD, O₂-TPD, DRIFTS, XPS and PXRD. It was shown that the SO₂ adsorption results in the formation of surface sulfate, while the uptake increased from 26 to 45 μmol/g with growing sulfur content of the model exhaust. The sulfur adsorption reduces the mobility and availability of oxygen on the catalyst thus inhibiting the oxygen transport from gas phase over the catalyst to the contact points of the soot. Consequently, the soot oxidation activity, investigated with tight contact blends of catalyst and soot, decreases with inclining amount of sulfate. Finally, the sulfate species were mostly removed by thermal treatment at 705 °C, which additionally provoked catalyst sintering. As a result, the catalytic performance of the de-sulfated catalyst was slightly lower compared to the sulfated sample.