Low-temperature NH3-SCR of NOx over MnCeOx/TiO2 catalyst: Enhanced activity and SO2 tolerance by modifying TiO2 with Al2O3

Abstract

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 MnCeOx 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 NOx with NH3 were evaluated at 50–250 °C and GHSV of 80000 mL/(gcat∙h). The results reveal that MnCeOx/TiO2–Al2O3 exhibits higher activity and better SO2 tolerance than MnCeOx/TiO2. Combining with the characterization results, the enhanced activity and SO2 tolerance of MnCeOx/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 MnCeOx/TiO2. Moreover, in situ DRIFTS was used to investigate the reaction mechanism, and the results indicate that the NH3-SCR reaction over MnCeOx/TiO2 and MnCeOx/TiO2–Al2O3 takes place by both the E–R and L–H mechanisms.