Low-temperature NH_3-SCR of NO_x over MnCeO_x/TiO_2 catalyst:Enhanced activity and SO_2 tolerance by modifying TiO_2 with Al_2O_3

A series of TiO₂–Al₂O₃ composites with Al/Ti molar ratios of 0.1, 0.2, and 0.4 were synthesized by a co-precipitation method and used as supports to prepare supported MnCeO_x catalysts by an impregnation method. The physico-chemical properties of the samples were extensively characterized by N₂ physisorption, X-ray diffraction, Raman spectroscopy, scanning electron microscopy and energy-dispersive X-ray spectroscopy element mapping, X-ray photoelectron spectroscopy, H₂-temperature programmed reduction, ammonia temperature programmed desorption, and in-situ diffuse reflectance infrared Fourier transform spectroscopy. The catalytic activity and resistance to water vapor and SO₂ of the as-prepared catalysts for the SCR of NO_x with NH₃ were evaluated at 50–250 °C and GHSV of 80000 mL/(g_cat?h). The results reveal that MnCeO_x/TiO₂–Al₂O₃ exhibits higher activity and better SO₂ tolerance than MnCeO_x/TiO₂. Combining with the characterization results, the enhanced activity and SO₂ tolerance of MnCeO_x/TiO₂–Al₂O₃ can be mainly attributed to higher relative concentrations of Mn⁴⁺ and chemisorbed oxygen species, stronger reducibility, and larger adsorption capacity for NH₃ and NO, which originate from the larger specific surface area and pore volume, higher dispersion of Mn and Ce species compared with MnCeO_x/TiO₂. Moreover, in situ DRIFTS was used to investigate the reaction mechanism, and the results indicate that the NH₃-SCR reaction over MnCeO_x/TiO₂ and MnCeO_x/TiO₂–Al₂O₃ takes place by both the E–R and L–H mechanisms.