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 NOx 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 NOx 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 NOx is observed at elevated pressures.