Promoted performance of a MnO_x/PG catalyst for low-temperature SCR against SO₂poisoning by addition of cerium oxide

Abstract

Manganese oxide supported palygorskite (MnO x /PG) catalysts are considered highly efficient for lowertemperature 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 SO 2 . In this study, we have doped the MnO x /PG catalyst with cerium oxide to improve their resistance against SO 2 poisoning. The SCR activity of the CeO 2 -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 SO 2 .Of all the different samples with different concentrations of Ce doping, the catalyst Mn 8 Ce 5 /PG exhibits the highest SCR activity in the presence of SO 2 -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 SO 2 -poisoning of the active species manganese oxides, which is widely believed to be one of the major reasons for the deactivation of manganesebased catalysts. However, the deposition of ammonium sulfates on the surface of catalysts, which is yet another important cause of SO 2 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 SO 2 poisoning.

A Review on Selective Catalytic Reduction of NOx by NH3 over Mn–Based Catalysts at Low Temperatures: Catalysts, Mechanisms, Kinetics and DFT Calculations

“…enhancing the resistance to H 2 O and SO 2 , the composite-oxides, such as Mn confined titania nanotubes (Mn/TNT)[99], M-Mn/TiO 2 (M = Fe[100][101][102][103][104], Co[105][106][107], Ce[105,108], Ni[109], W[110] etc. ), Fe-Mn/Ti-Zr[111], MnO x /Fe-Ti[112], MnO x /CeO 2 -TiO 2[113], Mn-Ce/PG (palygorskite)[114], MnO x /Ce 0.8 M 0.2 O 2 (M = Ti, Sn) [115], MnO x(0.6) /Ce 0.5 Zr 0.5 O 2 , [116] MnO 2 /Ce (1−x) Zr x O 2 -TiO 2 , [117] MnO 2 -Ce (1−x) Zr x O 2 /TiO 2 [118], SO 4 2Ho 0.1 Mn 0.4 /TiO 2 catalyst presented a broad operating temperature window in the range of 60-200 • C and exhibited superior sulfur-poisoning resistance with 80% NO x conversion in the presence of 200 ppm SO 2 and 15% H 2 O at 120 • C. Shen et al [116] found that MnO x(0.6) /Ce 0.5 Zr 0.5 O 2 displayed a good resistance to 3% H 2 O and 100 ppm SO 2 that remained 90% NO conversion at 180 • C over the course of 5 h. Qiu et al [119] found that the SO 4 2− -Mn-Co-Ce/Ti-Si catalyst has an excellent SO 2 durability at low temperatures. However, these catalysts show a relatively good resistance for a short time.…”

Byproduct Analysis of SO2 Poisoning on NH3-SCR over MnFe/TiO2 Catalysts at Medium to Low Temperatures

“…(2). the weight loss at 200-400 °C could be attributed to decomposition of ammonium salts [41][42][43].…”

Recent advances and perspectives in the resistance of SO2 and H2O of cerium-based catalysts for NOx selective catalytic reduction with ammonia

“…There are plenty of reviews for cerium-based catalysts. [43][44][45] Tang et al 43 explained the interaction between the active component and the reactants (NO, NH 3 and O 2 ) of ceriumbased catalysts in detail. Shan et al 44 comprehensively reviewed CeO 2 when used as a support, main active component, and promoter.…”