Low-temperature Fe–MnO2 nanotube catalysts for the selective catalytic reduction of NOx with NH3

Abstract

Exhaust gas from the sintering process in the iron and steel industry contains NO_x and SO₂ at low temperature. Therefore, the corresponding denitration catalyst should have favorable low-temperature activity and SO₂ resistance. In this study, an Fe-doped MnO₂ nanotube catalyst with the (211) crystal face synthesized using a one-step hydrothermal synthesis method demonstrated favorable pore structure and many weak acidic sites, which improved its low-temperature activity (>90% at 125–225 °C), N₂ selectivity (>90%), and SO₂ resistance. The NO conversion rate reached 94% when the Fe_0.5%MnO₂ catalyst was used in the presence of SO₂. Moreover, the Fe in the Fe_0.5%MnO₂ catalyst improved the reducibility of the surface Mn sites and reduced the oxidizing properties of bridging oxygen, resulting in easier conversion of Mn⁴⁺ to Mn³⁺ and affecting the regeneration of oxygen vacancies in the selective catalytic reduction of NO_x with NH₃ process. In situ diffuse reflectance infrared spectroscopy showed that the reduction of NO_x in the MnO₂ nanotubes and Fe_0.5%MnO₂ sample involved the Eley–Rideal mechanism, whereas the NH₃-SCR process of the Fe_5%MnO₂ sample involved both Langmuir–Hinshelwood and Eley–Rideal mechanisms.