The Influence Study Of CeO₂on MnO_x/PG Catalysts Resisted To SO₂Poisoning For Selective Catalytic Reduction Of NO By NH₃at Low Temperatures

The technology of selective catalytic reduction of NO with ammonia (NH3-SCR)is the main technical route that can meet the demand to remove the fixed andmobile sources of flue gas NO in the future. As we all know, the reactivetemperature window of the commercial SCR catalysts is narrow and the efficiencyof DeNOx is low. Therefore, it is a very considerable issue that has aroused wideattention of many researchers all over the world. Subsequently, a series oflow-temperature SCR catalysts have brought out. However, these catalysts aresensitive to the residual SO2in the flue gas and tent to get deactivated dramaticallyat low temperatures. Hence, based on the manganese oxides supported palygorskite(MnOx/PG) catalyst, we investigate the catalytic activity of catalyst doped ceriumoxide in SO2-containing gases.In this study, manganese oxides and metal oxides as additive were loadedsynchronously on the palygorskite. The additives include rare earth, alkaline earth(Ca, Mg) and some other metals. From the results of activity measurement andcharacterizations, it was found that CeO2doping can greatly enhance the catalyticactivity of the catalyst at low temperatures (the NO conversion was enhanced from47%to98%at150°C). Moreover, it has effectively improved the sulfur resistance.The doping of CeO2has promoted the transformation of Mn2O3and MnO2on thesurface of catalyst under the combined action of the lattice oxygen of CeO2and thegas oxygen, which was the main reason for improvement of activity at lowtemperature.Furthermore, the mechanism of SO2resistance was also investigated. It isinteresting to note that CeO2doping aggravates the oxidation of SO2to some extentand increased the deposition of ammonium salts. At the same time, the formation ofmanganese sulfate was restrained on the surface of catalyst, which promoted thestability of active species.When the reaction temperature was lower (lower than100oC), the deposition of ammonium salts was the dominant factor that resulted insulfur posining. As the reaction temperature was greatly increased, the formation ofmanganese sulfate became the dominant factor. However, manganese sulfate wasreduced with CeO2doping, and the catalytic activity was improved when thetemperature was higher than100oC. Finally, this paper studied the long-deactivation of catalyst in SO2-containinggases and investigated the effects of several different regeneration methods on thedeactivated catalyst. It was found that the catalyst wouldn’t be recovered both byheat treatment and water-washing.