The Synthesis And NH₃-SCR Performance Of Sulfur Doping Ce-based Catalyst

Nitrogen oxides?NO_x?is one of the major sources of air pollution.Ceria-based catalysts exhibit excellent performance in selective catalytic reduction of NO_x with NH₃.However,their activities are severely restrained in the presence of H₂O and SO₂.In this paper,Ce-based catalysts such as PS-NCLS and Cu-Ce?S?were prepared via precipitation method.The catalysts were modified by sulfur incorporation with SO₂ pre-treatment or sulfate precursor to improve resistance to H₂O and SO₂ of catalysts.The structure and morphology,reaction mechanism and the effect of modification of catalysts were characterized by X-ray diffraction?XRD?,transmission electron microscopy?TEM?,X-ray photoelectron spectroscopy?XPS?,temperature programmed desorption?TPD?,fourier transform infrared?FTIR?,in situ diffuse reflectance infrared fourier transform spectroscopy?DRIFTS?,thermogravimetry?TG?and other analytical methods.The NH₃-SCR activity and resistance to H₂O and SO₂ of catalysts were tested in fixed-bed reactor.For the PS-NCLS catalyst,La³⁺ has incorporated into the fluorite lattice of ceria and leads to the expansion of crystal cell which results in more lattice defects and improves the lattice oxygen mobility.Ni²⁺ enriches on the surface of sample and forms new Lewis acid sites.Sulfation treatment increases the proportion of Ce³⁺,chemisorbed oxygen,and improves the mobility of lattice oxygen.After sulfation treatment,the catalyst reserves the most of the Lewis acid sites and generates new Bronsted acid sites.Shrinking core model was proposed to explain sulfation process.In addition,in situ DRIFTS confirmed that the reaction mechanism of catalyst mostly follows the L-H mechanism.After sulfation treatment,PS-NCLS catalyst increases NH₃ adsorptivity and remains good NO adsorptivity in the coexistence of H₂O and SO₂.These results demonstrate that the introduction of Ni and La as well as sulfation treatment are responsible for excellent activity of NH₃-SCR and resistance to H₂O and SO₂ of PS-NCLS catalyst.For Cu-Ce?S?catalysts,with the increase in Cu incorporation amount,Cu²⁺ in Cu-Ce solid solution reaches saturation.CuO phase appears to disperse on the surface of the catalyst.The lower Cu incorporation content leads to higher Ce³⁺ ratio,which causes stronger Lewis acidity.The proportion of chemisorbed oxygen increases as Cu doping amount increases.The SO₄^2-in Cu-Ce?S?catalysts enhances Bronsted acidity of catalysts.Ammonium sulfite and ammonium sulfate were deposited on the surface of catalyst in the coexistence of water vapor and SO₂.However,the doping of Cu has an inhibitory effect on deposition phenomenon.3%Cu-Ce?S?catalyst has a wider temperature window and better NH₃-SCR activity as well as excellent resistance to H₂O and SO₂ than CeO₂ catalyst.