Effect of SO poisoning on undoped and doped Mn-based catalysts for selective catalytic reduction of NO

• Published in: Catalysis science & technology 2022-11, Vol.12 (22), p.6838-6848
• Main Authors: Ruiz-Martínez, Javier, Gevers, Lieven E, Enakonda, Linga R, Shahid, Ameen, Wen, Fei
• Format: Article
• ISSN: 2044-4753; 2044-4761
• DOI: 10.1039/d2cy01151d

In this work, the poisoning effect of SO 2 was investigated in binary MnTi and ternary MnCeTi mixed oxides for the NH 3 -SCR reaction under conditions relevant for mobile applications. For the binary MnTi sample, catalytic activity increases up to 250 °C, and then drops due to the oxidation of ammonia to NO x . The addition of Ce decreases the catalytic activity at 150 °C but widens the optimal operational temperature and reaches high conversion at 350 C. Upon performing activity test with 100 ppm of SO 2 in the gas stream, catalytic activity drastically decreases in all catalyst samples. The shape of the deactivation curve and SO 2 concentrations at the outlet of the reactor suggest a strong adsorption and poisoning of SO 2 on all the catalysts. Although samples containing large amounts of Ce display a better SO 2 tolerance, this is insufficient to be considered for practical applications. Deactivated samples were investigated by a wide range of characterization tools. N 2 physisorption measurements reveal a drop in the surface area that could partially explain catalyst deactivation. TGA reveals the absence of (NH 4 ) 2 SO 4 on the deactivated samples and suggests the formation of Mn and Ce sulfates on the catalyst surface. XPS results confirm the formation of MnSO 4 and also show a decrease in the Mn and Ce oxidation states. Analysis of the redox function by catalytic NO oxidation and H 2 -TPR experiments shows a strong loss of redox function upon SO 2 deactivation, which could explain the decrease of NH 3 -SCR catalytic activity. Upon unraveling the effect and cause of deactivation, a doping study was performed. As in the binary MnTi and ternary MnCeTi, catalytic activity strongly decreases upon the introduction of SO 2 in the gas stream. None of the dopants investigated was able to suppress SO 2 deactivation, which suggest that other dopants or strategies should be pursued to commercialize Mn-based catalysts for low-temperature applications. In real mobile applications, deactivation of Mn-based catalysts by SO 2 is severe and catalysts underperform at temperatures below 200 °C. SO 2 deactivates the catalysts' redox function and regeneration is cumbersome.