SO₂ Oxidation Across Marine V₂O₅-WO₃-TiO₂ SCR Catalysts: a Study at Elevated Pressure for Preturbine SCR Configuration

The undesired oxidation of SO₂ was studied experimentally at elevated pressures of up to 4.5 bar across two commercial vanadium-based (1.2 and 3 wt% V₂O₅) selective catalytic reduction (SCR) catalysts. This pressure range is of interest for preturbine SCR reactor configuration for NO_x reduction on ships. The residence time in the catalyst was kept constant, independent on pressure, by adjusting the total flow rate. The conversion of SO₂ was of the order 0.2–3% at temperatures of 300–400 °C and was independent of the pressure. Based on the measured conversion of SO₂, the kinetics were fitted using an nth order rate expression. The reaction order of SO₂ was found close to 1, and the reaction order of SO₃ was found close to 0, also at increased pressures of up to 4.5 bar. The rate of SO₂ oxidation was clearly promoted by the presence of 1000 ppm NO_x at elevated pressure; however, at atmospheric pressure, the effect was within experimental uncertainty. The promoting effect is explained by a catalyzed redox reaction between SO₂ and NO₂, and since more NO₂ is formed at elevated pressure, a higher degree of promotion by NO_x is observed at elevated pressures.