Catalytic Activity and Deactivation of SO2Oxidation Catalysts in Simulated Power Plant Flue Gases

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The catalyst deactivation and the simultaneous formation of compounds in commercial SO2oxidation catalysts have been studied by combined activity measurements andin situEPR spectroscopy in the temperature range 350–480°C. The applied feed gas compositions were 0.2% SO2, 4.5% O2, 15% CO2, and ∼80% N2; and 0.2% SO2, 4% O2, 7% H2O, 14% CO2, and ∼75% N2. These conditions simulate flue gas from coal fired power plants with and without water. It was shown that in both dry and wet flue gas, the V(IV) compound K4(VO)3(SO4)5precipitates below the temperature of catalyst deactivation. However, for a given catalyst composition, the deactivation temperature in the wet flue gas was strongly influenced by the structure of the support, whereas similar behaviour was not observed in the dry flue gas. Thus, one of the studied catalysts, with a particular pore structure, most probably a V(III) compound, precipitated first during deactivation in the wet flue gas, while the V(IV) compound, K4(VO)3(SO4)5, only precipitated with a further lowering of the temperature. Water vapour seems therefore to have a significant influence on the performance of the SO2-oxidation catalyst. A qualitative explanation is given for the formation of both V(IV) and V(III) compounds during deactivation.