Promoted performance of a MnOx/PG catalyst for low-temperature SCR against SO2 poisoning by addition of cerium oxide

Abstract

Manganese oxide supported palygorskite (MnO_x/PG) catalysts are considered highly efficient for lower-temperature selective catalytic reduction (SCR) of flue gas NO by ammonia. However, during the SCR reaction, the surface of the MnO_x/PG catalyst tends to get poisoned by SO₂. In this study, we have doped the MnO_x/PG catalyst with cerium oxide to improve their resistance against SO₂ poisoning. The SCR activity of the CeO₂-doped catalyst (Mn–Ce/PG) is found to be remarkably higher than that of the undoped MnO_x/PG catalyst in the temperature range of 100–200 °C in the presence of 400 ppm SO₂. Of all the different samples with different concentrations of Ce doping, the catalyst Mn₈Ce₅/PG exhibits the highest SCR activity in the presence of SO₂-containing gases. Systematic analyses of the sample performed by using XRD, XPS, SEM-EDS, temperature programmed desorption (TPD) and TGA suggest that the cerium oxide doping can obviously inhibit the SO₂-poisoning of the active species manganese oxides, which is widely believed to be one of the major reasons for the deactivation of manganese-based catalysts. However, the deposition of ammonium sulfates on the surface of catalysts, which is yet another important cause of SO₂ poisoning, can hardly be avoided via the addition of cerium oxide. On the basis of systematic studies, it can be assumed that the addition of cerium oxide can enhance the stability of the active species via the reduction of manganese sulfate rather than ammonium sulfates, thereby improving its resistance toward SO₂ poisoning.