Shuohan Yu

Fe-Mn/Al 2 O 3 catalysts for low temperature selective catalytic reduction of NO with NH 3

A series of Fe-Mn/Al 2 O 3 catalysts were prepared and studied for low temperature selective catalytic reduction (SCR) of NO with NH 3 in a fixed-bed reactor. The effects of Fe and Mn on NO conversion and the deactivation of the catalysts were studied. N 2 adsorption-desorption, X-ray diffraction, transmission electron microscopy, energy dispersive spectroscopy, H 2 temperature-programmed reduction, NH 3 temperature-programmed desorption, X-ray photoelectron spectroscopy (XPS), thermal gravimetric analysis and Fourier transform infrared spectroscopy were used to characterize the catalysts. The 8Fe-8Mn/Al 2 O 3 catalyst gave 99% of NO conversion at 150 ℃ and more than 92.6% NO conversion was obtained in a wide low temperature range of 90-210 ℃. XPS analysis demonstrated that the Fe 3+ was the main iron valence state on the catalyst surface and the addition of Mn increased the accumulation of Fe on the surface. The higher specific surface area, enhanced dispersion of amorphous Fe and Mn, improved reduction properties and surface acidity, lower binding energy, higher Mn 4+ /Mn 3+ ratio and more adsorbed oxygen species resulted in higher NO conversion for the 8Fe-8Mn/Al 2 O 3 catalyst. In addition, the SCR activity of the 8Fe-8Mn/Al 2 O 3 catalyst was only slightly decreased in the presence of H 2 O and SO 2 , which indicated that the catalyst had better tolerance to H 2 O and SO 2 . The reaction temperature was crucial for the SO 2 resistance of catalyst and the decrease of catalytic activity caused by SO 2 was mainly due to the sulfate salts formed on the catalyst.

Preparation, characterization, and catalytic performance of high efficient CeO 2 -MnO x -Al 2 O 3 catalysts for NO elimination

A series of CeO 2 -MnO x -Al 2 O 3 mixed oxide catalysts (Ce:Mn:Al mole ratio = 6:4: x , x = 0.25, 0.5, 1, 2) were prepared by a simple one-step inverse co-precipitation method to investigate the influence of the incorporation of Al 3+ into CeO 2 -MnO x mixed oxides. CeO 2 -MnO x , CeO 2 -Al 2 O 3 , and MnO x -Al 2 O 3 mixed oxides, and CeO 2 were prepared by the same method for comparison. The samples were characterized by XRD, Raman, N 2 physisorption, H 2 -TPR, XPS, and in situ DRIFTS. The catalytic reduction of NO by CO was chosen as a model reaction to evaluate the catalytic performance. The incorporation of a small amount of Al 3+ into CeO 2 -MnO x mixed oxides resulted in a decrease of crystallite size, with the increase of the BET specific surface area and pore volume, as well as the increase of Ce 3+ and Mn 4+ . The former benefits good contact between catalyst and reactants, and the latter promotes the adsorption of CO and the desorption, conversion and dissociation of adsorbed NO. All these enhanced the catalytic performance for the NO+CO model reaction. A reaction mechanism was proposed to explain the excellent catalytic performance of CeO 2 -MnO x -Al 2 O 3 catalysts for NO reduction by CO.

Construction of hybrid multi-shell hollow structured CeO2–MnOx materials for selective catalytic reduction of NO with NH3

Hollow structured CeO2–MnOx hybrid materials with up to three shells were prepared successfully by using carbon spheres as the hard template. It was found that the shells could be well controlled by simply adjusting the calcination rate. Elemental mapping results showed Mn and Ce species exhibited a homogeneous spatial distribution and the existence of Mn could improve the diffusion of CeO2 into the carbon spheres during the construction of the multi-shell structure, suggesting the intensive cooperative interaction between Mn and Ce. When triple-shell CeO2–MnOx hollow spheres were used as a catalyst for selective catalytic reduction of NO with NH3, superior low-temperature catalytic performance was exhibited, compared with traditional CeO2–MnOx nanoparticles, single-shell and double-shell hollow spheres. Combined with XRD, H2-TPR and XPS characterization, it was indicated that the synergistic effects and surface active species enhanced by the special multi-shell CeO2–MnOx hollow structures could account for the excellent performances. The results of the present study shed light on the creation of complex and hybrid hollow structured materials for superior performance in catalysis fields, like NO reduction for environmental protection.

Synthesis of CrOx/C catalysts for low temperature NH3-SCR with enhanced regeneration ability in the presence of SO2

Chromium oxide nano-particles with an average diameter of 3xa0nm covered by amorphous carbon (CrOx/C) were successfully synthesized. The synthesized CrOx/C materials were used for the selective catalytic reduction of NOx by NH3 (NH3-SCR), which shows superb NH3-SCR activity and in particular, satisfactory regeneration ability in the presence of SO2 compared with Mn-based catalysts. The as-prepared catalysts were characterized by XRD, HRTEM, Raman, FTIR, BET, TPD, TPR, XPS and in situ FTIR techniques. The results indicated presence of certain amounts of unstable lattice oxygen exposed on the surface of CrOx nano-particles with an average size of 3 nm in the CrOx/C samples, which led to NO being conveniently oxidized to NO2. The formed NO2 participated in NH3-SCR activity, reacting with catalysts via a “fast NH3-SCR” pathway, which enhanced th NH3-SCR performance of the CrOx/C catalysts. Furthermore, the stable lattice of the CrOx species made the catalyst immune to the sulfation process, which was inferred to be the cause of its superior regeneration ability in the presence of SO2. This study provides a simple way to synthesize stable CrOx nano-particles with active oxygen, and sheds light on designing NH3-SCR catalysts with highly efficient low temperature activity, SO2 tolerance, and regeneration ability.