New Insight into the Effects of NH₃ on SO₂ Poisoning for In Situ Removal of Metal Sulfates in Low-Temperature NH₃-SCR over an Fe–V Catalyst

Abstract

SO2 poisoning is a significant challenge for low-temperature selective catalytic reduction of NO x with NH3. Fundamental understanding of such sulfation effects on the catalyst is an essential step for finding strategies to overcome the issue. Here, the effect of NH3 on the temperature-driven sulfation process is systematically investigated over an Fe–V catalyst composed of α-Fe2O3 and FeVO4. When poisoning occurred by SO2 + O2, the highly dispersed and thermally stable Fe2(SO4)3 species would be formed on the catalyst surface. Such poisoning was getting worse with the increase of sulfation temperature, inducing the continuous lowering of redox properties, NO x activation ability, and thereby the low-temperature catalytic performance. With introduction of NH3, additional ammonium sulfates species were simultaneously generated at lower temperatures (<250 °C), covering the surface reaction sites and thus aggravating the decline of low-temperature activities. Whereas the formation of Fe2(SO4)3 species would be dramatically suppressed at higher sulfation temperatures (≥250 °C), it reduces the poisoning effects that occur at low reaction temperatures. The sulfated catalyst with the stable Fe2(SO4)3 species can be in situ regenerated through NH3 reduction followed by thermal treatment. Remarkably, compared with the fresh catalyst, the regenerated catalyst exhibited equivalent surface/redox properties and the consequent catalytic performance.

Review of Sulfur Promotion Effects on Metal Oxide Catalysts for NOx Emission Control

“…Here, several possible directions and methods for follow-up research are proposed. It is hard to maintain appropriate sulfate content over metal oxides without continuous decompositions or accumulations during the reaction. In situ SO 2 sulfation treatment effectively prevented the conversion of surface sulfates to bulk sulfates and maintained the interfacial effects with an appropriate sulfate content. , CeO 2 –SiO 2 and CeO 2 –ZrO 2 catalysts were fabricated with the characteristics of high surface area and moderate sulfate storage to make full use of the adsorption and activation characteristics of sulfates. Besides, simple N 2 /Ar/NH 3 thermal treatment was proved to eliminate sulfates without affecting the surface area and redox characteristics over specific CeO 2 and Fe 2 O 3 catalysts. The synergistic catalysis between acid and metal sites and the interfacial effect caused by sulfates were not fully understood.…”

“…Various characterization results indicated that sulfates would not commonly combine with V 2 O 5 domains because of the relatively weak binding energy between sulfates and V 2 O 5 compared to other metal oxides like CeO 2 , Fe 2 O 3 , TiO 2 , , etc. Baraket et al reported that sulfates broadened the operating temperature window of V 2 O 5 /TiO 2 to the range of 300 and 400 °C.…”

Peanut-Shaped Cu–Mn Nano-Hollow Spinel with Oxygen Vacancies as Catalysts for Low-Temperature NO Reduction by CO

“…According to the results, the apparent activation energy ( E a ) of Cu 0.75 Mn 2.25 O 4 -NH (36.4 kJ·mol –1 ) is obviously lower than that of Cu 0.75 Mn 2.25 O 4 -NP (70.9 kJ·mol –1 ). This illustrates that the nanostructure could reduce the reaction barriers and improve the catalytic performance. , …”

“…This illustrates that the nanostructure could reduce the reaction barriers and improve the catalytic performance. 48,49 It is well known that the higher gas hourly space velocity (GHSV), the more economical operation. The results in Figure 5d reveal the catalytic performance of Cu 0.75 Mn 2.25 O 4 -NH under different GHSV (30 000−70 000 h −1 ) conditions.…”

Recent advances in heighten sulfur resistance of SCR catalysts: A review

“…Team of Professor Li from Dalian University of Technology [46] proposed that the sulfation tends to have a negative effect on the low-temperature reaction of FeVOx catalyst, but actively promotes high-temperature activity by inhibiting harmful NH3 oxidation. Li et al [47] found that V−W/Ce/Ti-5% presented better NH3-SCR activity and higher NH4HSO4 resistance at 280°C when 5% WO3 was loaded.…”