Low-temperature catalytic reduction of nitrogen oxides over manganese-cerium composite oxides supported on zirconium-doped titanium dioxide

Carriers of TiO₂, ZrO₂ and TiO₂-ZrO₂ with different ratios were prepared by sol-gel method. Some manganese-cerium (Mn-Ce) active components were loaded on these carriers by ultrasonic immersion. The catalysts were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR) spectroscopy, and Brunauer-Emmett-Teller (BET) method. The activity of the catalysts was studied under the condition of low-temperature catalytic reduction of NO_x with ammonia as a reductant. The results show that the TiO₂-ZrO₂ (3:1, molar ratio) carrier was a mesoporous material, the particle size is smaller, the particles are highly dispersed, and the specific surface area reaches up to 151 m²· g^-1. By doping ZrO₂, Zr⁴⁺ ions replace Ti⁴⁺ ions and enter the lattice, leading to TiO₂ lattice distortion. The addition of ZrO₂ inhibits crystal transfer from anatase to rutile phase, and so the thermal stability of this carrier improves. Furthermore, the active components mainly exist in amorphous state and the Ce³⁺/Ce⁴⁺ redox couple appears on the carrier surface, thus the catalytic reduction activity at low temperature improves. The highest activity of the 10% Ce(0.4)-Mn/TiO₂-ZrO₂ (3:1) catalyst is obtained under calcination at 550℃. At 140℃ and a space velocity of 67000 h-1, the conversion rate of NO_x reaches 99.28%. The 10% Ce(0.4)-Mn/TiO₂-ZrO₂ (3:1) catalyst provides strong anti-poisoning capacity to H₂O and SO₂ in the presence of 10% H₂O alone, or 10% H₂O with 2×10^-4 SO₂ at 140℃.