Pijun Gong

Effects of surface physicochemical properties on NH 3 -SCR activity of MnO 2 catalysts with different crystal structures

Abstract α-, β-, δ-, and γ-MnO2 nanocrystals are successfully prepared. We then evaluated the NH3 selective catalytic reduction (SCR) performance of the MnO2 catalysts with different phases. The NOx conversion efficiency decreased in the order: γ-MnO2 > α-MnO2 > δ-MnO2 > β-MnO2. The NOx conversion with the use of γ-MnO2 and α-MnO2 catalysts reached 90% in the temperature range of 140–200 °C, while that based on β-MnO2 reached only 40% at 200 °C. The γ-MnO2 and α-MnO2 nanowire crystal morphologies enabled good dispersion of the catalysts and resulted in a relatively high specific surface area. We found that γ-MnO2 and α-MnO2 possessed stronger reducing abilities and more and stronger acidic sites than the other catalysts. In addition, more chemisorbed oxygen existed on the surface of the γ-MnO2 and α-MnO2 catalysts. The γ-MnO2 and α-MnO2 catalysts showed excellent performance in the low-temperature SCR of NO to N2 with NH3.

Performance regulation of Mn/TiO2 catalysts by surfactants for the selective catalytic reduction of NO with NH3 at low temperatures

A series of Mn/TiO2 catalysts were prepared using different dosage of cetyl trimethyl ammonium bromide (CTAB) and polyethylene glycol (PEG) 600 as surfactants by sol–gel method. When CTAB/Ti and PEG/Ti were 0.075 and 0.13, the morphology of the catalysts exhibited nano rod and regular sphere structure, respectively, and the activity was also the highest. The superior SCR activity of NC(0.075)-Mn/TiO2 and NP(0.13)-Mn/TiO2 catalysts was mainly due to the larger surface area and stronger reduction ability. In addition, it was found that the SCR activity of the catalysts with PEG600 as surfactants was generally higher than that of CTAB as surfactants, which may be due to its advantages in specific surface area, crystallinity, acidity, surface ion and chemisorbed oxygen concentration, and reducibility.

NH 3 -SCR Activity of MnOx/CeO 2 Catalyst at Low Temperature

In this paper, CeO2 was synthesized and used as carrier, meanwhile, MnOx was supported by different methods. The NH3-SCR activity of MnOx/CeO2 at low temperature has also been studied. The results show that the performance of the MnOX/CeO2 catalyst prepared by hydrothermal deposition method (MC-h) can reach up to 80% at 180 ℃, while the impregnation method (MC-i) is only 70% at 180 ℃. Testing results indicate that the catalysts synthesized by the hydrothermal deposition method have larger specific surface area and higher reducibility, and manganese oxide existed in the form of nanorods is more favorable for the contact between the active component and the reactive gas. All of these are beneficial to the SCR reaction.

Effect of Calcination Temperature on the SCR Activity of Fe–S/TiO 2 Catalysts

A series of Fe–S/TiO2 catalysts were prepared at different calcination temperatures by impregnation method and its performance of selective catalytic reduction (SCR) of NO with NH3 was investigated at temperatures ranging from 200 to 400 °C. Fe–S/TiO2-300 °C catalyst showed the highest activity, the NO conversion reaching over 80% in the range of 280–400 °C. With the help of XRD, H2-TPR and NH3-TPD, the structures and properties of catalysts were characterized. With the increase of calcination temperature, the Fe(OH)SO4 content in the catalyst decreased gradually. In addition, When the calcination temperature was below 400 °C, the main crystal phase in the catalyst is Fe(OH)SO4 and FeSO4. However, when it was 500 °C, the crystal phase of the active material became Fe2(SO4)3 and FeSO4. What’s more, the reduction ability of several catalysts showed no much difference, but the surface acidity was quite different, as the acidity of the Fe–S/TiO2-300 °C catalyst was the strongest.