Si-modified Mn–Ce oxide catalysts for selective catalytic reduction of NOx with NH3 at low temperatures

Abstract

Si-modified Mn–Ce oxide catalysts were prepared by a co-precipitation method for the selective catalytic reduction of NO_x with NH₃ (NH₃-SCR). The doping of Si can improve significantly the NO_x conversion and N₂ selectivity of the Mn–Ce oxide catalysts above 150 °C. The catalyst with Mn : Ce : Si = 4 : 5 : 1 molar ratio (Mn₄Ce₅Si₁) showed excellent SCR activity at low temperatures, with NO_x conversion above 80% at 110–230 °C. The further acid modification could broaden the operating temperature window of Mn₄Ce₅Si₁, and Mn₄Ce₅Si₁-1%S exhibited higher deNO_x efficiency (>90%) from 100 to 260 °C. The Si modification increased the specific surface area and surface acidity, and facilitated the NO/NH₃ adsorption, thus enhancing the low-temperature activity through both Langmuir–Hinshelwood (L–H) and Eley–Rideal (E–R) pathways. The N₂O production over Mn–Ce oxide catalysts through the L–H mechanism was much lower than via the E–R mechanism.