Hsunling Bai

The byproducts of ammonia-selective catalytic reduction (NH₃-SCR) process over MnFe/TiO₂ catalysts under the conditions of both with and without SO₂ poisoning were analyzed. In addition to the NH₃-SCR reaction, the NH₃ oxidation and the NO oxidation reactions were also evaluated at temperatures of 100–300 °C to clarify the reactions occurred during the SCR process. The results indicated that major byproducts for the NH₃ oxidation and NO oxidation tests were N₂O and NO₂, respectively, and their concentrations increased as the reaction temperature increased. For the NH₃-SCR test without the presence of SO₂, it revealed that N₂O was majorly from the NH₃-SCR reaction instead of from NH₃ oxidation reaction. The byproducts of N₂O and NO₂ for the NH₃-SCR reaction also increased after increasing the reaction temperature, which caused the decreasing of N₂-selectivity and NO consumption. For the NH₃-SCR test with SO₂ at 150 °C, there were two decay stages during SO₂ poisoning. The first decay was due to a certain amount of NH₃ preferably reacted with SO₂ instead of with NO or O₂. Then the catalysts were accumulated with metal sulfates and ammonium salts, which caused the second decay of NO conversion. The effluent N₂O increased as poisoning time increased, which was majorly from oxidation of unreacted NH₃. On the other hand, for the NH₃-SCR test with SO₂ at 300 °C, the NO conversion was not decreased after increasing the poisoning time, but the N₂O byproduct concentration was high. However, the SO₂ led to the formation of metal sulfates, which might inhibit NO oxidation reactions and cause the concentration of N₂O gradually decreased as well as the N₂-selectivity increased.

A series of iron-manganese oxide catalysts supported on TiO2 and titanium nanotubes (TNTs) were studied for low temperature selective catalytic reduction (SCR) of NO with NH3 in the presence of SO2. The results showed that the specific surface area and the amount of Brønsted acid sites were highly correlated. The results also demonstrated that higher Mn4+/Mn3+ ratios and larger specific surface areas might be the main reasons for the excellent performance of MnFe-TNTs catalyst after SO2 poisoning. The SO2 poisoning effect could be minimized by reducing the GHSV, increasing the reaction temperature, or increasing the [NH3]/[NO] molar ratio. The results also indicated that the formation of ammonium sulfate had a stronger effect on the NO conversion efficiency as compared to the formation of metal sulfate. Thus operating the low temperature SCR at above 230 oC to avoid the formation of ammonium sulfate would be the priority choice when SO2 poisoning is a concerned issue. Implications: Low-temperature selective catalytic reduction (SCR) has attracted increasing attention due to that it can reduce the energy consumption for the SCR process employed in industries such as steel plants and glass manufacturing plants. However, it also suffers from the sulfur dioxide (SO2) poisoning problem. This study investigates the possibility of using titania nanotubes (TNTs) as the support of Mn/Fe bimetal oxide catalysts for low-temperature SCR to reduce the SO2 poisoning. The results indicated that the MnFe-TNT catalyst can tolerate SO2 for a longer time as compared with the MnFe-TiO2 catalyst.

The CoO_x/SiO₂ spherical particles with hollow or mesoporous structure were successfully prepared by spray pyrolysis by using the NaCl and NaNO₃ as in situ formed templates for the first time.

The removals of NO_x by catalytic technology at low temperatures (100–300 °C) for industrial flue gas treatment have received increasing attention. However, the development of low temperature catalysts for selective catalytic reduction (SCR) of NO_x with ammonia is still a challenge especially in the presence of SO₂. The current status of using Mn-based catalysts for low temperature SCR of NO_x with ammonia (NH₃-SCR) is reviewed. Reaction mechanisms and effects of operating factors on low temperature NH₃-SCR are addressed, and the SCR efficiencies of Mn-based metal oxides with and without SO₂ poisoning have also been discussed with different supports and co-metals. The key factors for enhancing low temperature NH₃-SCR efficiency and SO₂ resistance with Mn-based catalysts are identified to be (1) high specific surface area; (2) high surface acidity; (3) oxidation states of manganese; (4) well dispersion of manganese oxide metals; (5) more surface adsorbed oxygen; (6) more absorbed NO₃⁻ on the catalyst surface; (7) easier decomposition of ammonium sulfates. Moreover, the regenerative methods such as water washing, acid and/or alkali washing and heat treatment to the poisoned catalysts could help to recover the low temperature SCR efficiency to its initial level.

In this study, the photocatalytic reduction of CO₂ in a monoethanolamine solution to form valuable energy sources was investigated using Mo-doped TNTs photocatalysts for the first time.