Doping effect of cations(Zr^(4+),Al^(3+),and Si^(4+)) on MnO_x/CeO_2 nano-rod catalyst for NH_3-SCR reaction at low temperature

Thermally stable Zr4+, Al3+, and Si4+ cations were incorporated into the lattice of CeO2 nano‐rods (i.e., CeO2‐NR) in order to improve the specific surface area. The undoped and Zr4+, Al3+, and Si4+ doped nano‐rods were used as supports to prepare MnOx/CeO2‐NR, MnOx/CZ‐NR, MnOx/CA‐NR, and MnOx/CS‐NR catalysts, respectively. The prepared supports and catalysts were comprehensively characterized by transmission electron microscopy (TEM), high‐resolution TEM, X‐ray diffraction, Raman and N2‐physisorption analyses, hydrogen temperature‐programmed reduction, ammonia temperature‐programmed desorption, in situ diffuse reflectance infrared Fourier‐transform spectroscopic analysis of the NH3 adsorption, and X‐ray photoelectron spectroscopy. Moreover, the catalytic performance and H2O+SO2 tolerance of these samples were evaluated through NH3‐selective catalytic reduction (NH3‐SCR) in the absence or presence of H2O and SO2. The obtained results show that the MnOx/CS‐NR catalyst exhibits the highest NOx conversion and the lowest N2O concentration, which result from the largest number of oxygen vacancies and acid sites, the highest Mn4+ content, and the lowest redox ability. The MnOx/CS‐NR catalyst also presents excellent resistance to H2O and SO2. All of these phenomena suggest that Si4+ is the optimal dopant for the MnOx/CeO2‐NR catalyst.

Doping effect of rare earth metal ions Sm^(3+),Nd^(3+)and Ce^(4+)on denitration performance of MnO_(x) catalyst in low temperature NH_(3)-SCR reaction

The MnXO_(x) catalysts(i.e.,MnSmO_(x),MnNdO_(x),MnCeO_(x)) were prepared by reverse co-precipitation method and used for NH_(3)-SCR reaction.It is found that MnCeO_(x) catalyst presents the best low tempe rature catalytic activity(higher than 90% NO_(x) conversion in the te mperature range from 125 to 225℃)and excellent H_(2)O+SO_(2) resistance.In order to explore the reason for this result,the characterization of X-ray diffraction(XRD),Raman spectroscopy,Brunauer-Emmett-Teller(BET),H_(2)-temperature programmed reduction(H_(2)-TPR),NH_(3)-temperature programmed desorption(NH_(3)-TPD),X-ray photoelectron spectroscopy(XPS) and in situ diffuse reflaxions infrared Fourier transformations spectroscopy(DRIFTS) were conducted.The obtained results suggest that MnCeO_(x) catalyst shows the largest amount of acid sites and the best reducibility among these MnXO_(x) catalysts.Besides,Ce^(4+) doping inhibits the crystallization of MnO_(x) catalyst and shows the largest specific surface area.Finally,in situ DRIFTS experiments reveal that NH_(3)-SCR reaction over MnCeO_(x) catalyst follows both Langmuir-Hinshelwood(LH) and Eley-Rideal(E-R) mechanisms,which is through "fast SCR" reaction.

Effects of different introduction methods of Ce^4+and Zr^4+on denitration performance and anti-K poisoning performance of V2O5-WO3/TiO2 catalyst

The purpose of this work is to explore the effects of the introduction methods of Ce^4+and Zr^4+on the physicochemical properties,activity,and K tolerance of V2 O5-WO3/TiO2 catalyst for the selective catalytic reduction of NOx by NH3.Four different methods,namely pre-impregnation,post-impregnation,coimpregnation,and co-precipitation,were used to synthesize a series of V2 O5-WO3-TiO2-CeO2-ZrO2 catalysts.The catalysts were characterized by XRD,BET,NH3-TPD,XPS,and H2-TPR techniques.Moreover,the activity and anti-K poisoning performance were tested by an NH3-SCR model reaction.The results show that the introduction of Ce^4+and Zr^4+can improve the catalytic performance of V2O5-WO3/TiO2 catalyst,but the impregnation method cannot enhance the anti-K poisoning performance.Ce^4+and Zr^4+introduced by co-precipitation method can effectively improve the tolerance of K,which is mainly due to the incorporation of Ce^4+and Zr^4+into TiO2 lattice to form a uniform TiO2-CeO2-ZrO2 solid solution,resulting in the optimal surface acidity and redox performance,and reducing the decreases caused by Kpoisoning.Furthermore,based on the best introduction method,we further optimized the molar ratio of Ce^4+/Zr^4+,It is found that the catalyst exhibits the best anti-K poisoning performance when the molar ratio of Ce^4+/Zr^4+is 2:1.