Effect of synthesis methods on activity of V_2O_5/CeO_2/WO_3-TiO_2 catalyst for selective catalytic reduction of NO_x with NH_3

The effect of synthesis methods on the activity of V/Ce/WTi catalysts was investigated for the selective catalytic reduction(SCR) of NO_x by NH_3. V/Ce/WTi-DP(deposition precipitation) catalyst showed excellent NH_3-SCR performance, especially the better medium-temperature activity and the less N_2O formation than V/Ce/WTi-IMP(impregnation). These catalysts were characterized by X-ray diffraction(XRD), Brumauer-Emmett-Teller(BET), X-ray photoelectron spectroscopy(XPS), temperature-programmed reduction(H_2-TPR), and in situ DRIFTS techniques. The XPS and H_2-TPR results revealed that V/Ce/WTi-DP exhibited more surface Ce species, higher level of Oα and higher reducibility of Ce species. Reflected by in situ DRIFTS results, the deposition precipitation method(DP) contributed to a greater amount of weakly adsorbed NO_2, monodentate nitrate and NH_3 species with better reactive activity. Meanwhile, the cis-N_2O_2~(2–) species, an intermediate for N_2O formation, was very limited. As a result, these advantages brought about the superior SCR activity and N_2 selectivity for V/Ce/WTi-DP.     

Hydrothermal and sulfur aging of CeTi/CeWTi catalysts for selective catalytic reduction of NO_x with NH_3

The CeO_2-TiO_2(CeTi)and CeO_2/WO_3-TiO_2(CeWTi)catalysts were prepared by sol-gel method.The asprepared catalysts were hydrothermally treated at 760 ℃ for 48 h in air containing 10 vol% H_2O to obtain the hydrothermal aged catalysts.The sulfur aged catalysts were treated at 400 ℃ with 100 ppm SO_2,10%water vapor,air balance for 48 h and catalysts.The powder X-ray diffraction(XRD)and Raman results indicate that the crystallization of hydrothermal aged catalysts is more serious than sulfur aged catalysts.In addition,tungsten species can stabilize the CeTi catalyst from grain growth.According to the results of in situ diffuse reflectance infrared Fourier transform spectra(DRIFTS),temperatureprogrammed desorption of ammonia(NH_3-TPD),H_2 temperature-programmed reduction(H_2-TPR)and ammonia oxidation,the aging process leads to loss of surface area,redox properties,surface acidities and surface ceria concentration,especially for the hyd rothermal aging.The NH_3-NO/NO_2 SCR perfo rmances of sulfur aged catalysts are better than that of hydrothermal aged catalysts.Compared with CeTi catalyst,the addition of tungsten inhibits the crystallization of catalyst.So that more acid sites and active sites are retained.This is also the reason why tungsten addition improves the NH_3-NO/NO_2 SCR performance of CeTi catalyst.     

In-situ DRIFT assessment on strengthening effect of cerium over FeO_x/TiO_2 catalyst for selective catalytic reduction of NO_x with NH_3

Fe-based catalysts have a great potential to be used for selective catalytic reduction(SCR) of NO_x with NH3 reaction due to their low cost,nontoxicity and excellent catalytic activity.The aim of this paper is to investigate Ce doping effect on activity of NH_3-SCR over the FeO_x/TiO_2 catalyst.In-situ diffuse reflectance infrared fourier transform(DRIFT) technology was utilized to verity the adsorbed species on the surface of FeO_x/TiO_2 and FeO_x-CeO_2/TiO_2 catalysts.With respect to the obtained results,among the four catalysts studied,the FeO_x-CeO_2/TiO_2 with the FeO_x/CeO_2 ratio of 3/8 shows the best NO conversion more than 98%in the temperature range of 230—350℃,The active centers for NH_3 adsorption and activation are assigned to Lewis acid sites over the FeO_x-CeO_2/TiO_2 and monodentate nitrates can act as the key intermediate in the NH3-SCR.Moreover,both of Langmuir-Hinshelwood and Eley-Rideal mechanisms are observed over the FeO_x-CeO_2/TiO_2 catalysts in the SCR.     

Effect of praseodymium additive on CeO_2(ZrO_2)/TiO_2 for selective catalytic reduction of NO by NH_3

A series of praseodymium added CeO_2(ZrO_2)/TiO_2 catalysts separately prepared by methods of sol-gel and impregnation were tested for selective catalytic reduction of NO, and characterized by X-ray diffraction(XRD), N_2-brumauer-emmett-teller(N_2-BET), NH_3-temperature programmed desorption(NH_3-TPD), H_2-temperature programmed reduction(H_2-TPR), PL spectra, Raman spectra, electron paramagnetic resonance(EPR) and X-ray photoelectron spectroscopy(XPS), respectively. Influence of preparation method on catalytic performance was studied. Results showed that the influence of Pr addition on catalytic performance of the CeO_2(ZrO_2)/TiO_2 catalysts was different between the sol-gel method and the impregnation method. The Pr addition tended to interact with TiO_2 and formed the structure of Ti-O-Pr in the sol-gel method while it was more likely to interact with CeO_2 forming the structure of Ce-O-Pr in the impregnation method. The total acid amount and redox properties of the catalysts prepared by sol-gel method decreased with the addition of Pr element, which resulted in decrease of catalytic activity. In contrast, the Pr-added catalyst prepared by impregnation method was found to possess easier reducibility, more total acid amount and higher proportion of Ce~(3+) species, which was favourable for higher catalytic activity.     

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 TiO_2-Al_2 O_3 composites with Al/Ti molar ratios of 0.1,0.2,and 0.4 were synthesized by a coprecipitation 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 micro scopy and energy-dispersive Xray spectroscopy element mapping,X-ray photoelectron spectroscopy,H_2-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 SO_2 of the asprepared catalysts for the SCR of NO_x with NH3 were evaluated at 50-250℃ and GHSV of 80000 mL/(g_(cat)·h).The results reveal that MnCeO_x/TiO_2-Al_2 O_3 exhibits higher activity and better SO2 tolerance than MnCeO_x/TiO_2.Combining with the characterization results,the enhanced activity and SO2 tolerance of MnCeO_x/TiO_2-Al_2 O_3 can be mainly attributed to higher relative concentrations of Mn~(4+)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/TiO_2.Moreover,in situ DRIFTS was used to investigate the reaction mechanism,and the results indicate that the NH3-SCR reaction over MnCeO_x/TiO_2 and MnCeO_x/TiO_2-Al_2 O_3 takes place by both the E-R and L-H mechanisms.     

Promotional effects of copper doping on Ti-Ce-O_x for selective catalytic reduction of NO by NH_3 at low temperature

A series of copper-doped Ti-Ce-O_x complex oxide catalysts were synthesized by sol-gel method and evaluated for selective catalytic reduction of NO by NH_3 at low temperature. The promotional effect of copper doping on their structure, acidity and catalytic activity were investigated by means of Brumauer-Emmett-Teller(BET), temperature-programmed reduction(H_2-TPR), X-ray diffraction(XRD), scanning electron microscopy(SEM), temperature programmed desorption(NH_3-TPD) and pyridine adsorption infrared spectrum(Py-IR) technologies. Results showed that the copper additives could improve the low temperature catalytic performance for selective catalytic reduction of Ti-Ce-O_x catalyst and the NO conversion efficiency of Ti-Cu-Ce-O_x catalyst reached above 90% at 150–250 oC(Ti/Cu=4). The introduction of copper could enhance the redox property of the Ti-Ce-O_x complex oxide catalyst, refine the particle size caused by lattice distortion and oxygen vacancy defect and enhance the acid amount of the Lewis acid site. Moreover, Ti-Cu-Ce-O_x complex oxide catalyst also had good anti-sulfur ability and anti-water influence, when injecting 300 ppm SO_2 and 10 vol.%H_2O, the NO conversion efficiency of Ti-Cu-Ce-O_x catalyst reached 80%.     

Modification of Cu/ZSM-5 catalyst with CeO_2 for selective catalytic reduction of NO_x with ammonia

Cu/ZSM-5 and CeO_2-modified Cu/ZSM-5 catalysts were prepared by a wetness impregnation method. The addition of CeO_2 was found to enhance the NO_x selective catalytic reduction(SCR) activity of the catalyst at low temperatures, but the high-temperature activity was weakened. The catalysts were characterized by X-ray diffraction(XRD), nitrogen physisorption, inductively coupled plasma optical emission spectrometry(ICP-OES), X-ray photoelectron spectroscopy(XPS), electron paramagnetic resonance(EPR), H_2 temperature-programmed reduction(TPR) and NH_3 temperature-programmed desorption(TPD). The results showed that more CuO clusters instead of isolated Cu~(2+) species were obtained on the modified catalyst. These active CuO clusters, as well as the Cu-Ce synergistic effect, improved the redox property of the catalyst and low-temperatures SCR activity via promoting the oxidation of NO to NO_2 and fast SCR reaction. The loss in high-temperatures activity was attributed to the enhanced competitive oxidation of NH_3 by O_2 and decreased surface acidity of the catalyst.     

Rare earth containing catalysts for selective catalytic reduction of NO_x with ammonia:A Review

Increasingly stringent regulations in many countries require effective reduction and control of NOx emissions. To meet these limits, various methods have been exploited, among which the selective catalytic reduction of NOx using ammonia as the reductant(NH3-SCR) is the most favored technology. High catalytic activity, N2 selectivity and resistance to deactivation by sulfur, alkaline metals and hydrothermal conditions are the optimal properties of a successful SCR catalyst. Rare earth oxides, particularly CeO2, have been increasingly used to improve the catalytic activity and resistance to deactivation of deNOx catalysts, both modifying traditional vanadium catalysts, and also developing novel catalysts, especially for low temperature applications. This review summarized the open literature concerning recent research and development progresses in the application of rare earths for NH3-SCR of NOx. Additionally, the roles of rare earths in enhancing the performance of NH3-SCR catalyst were reviewed.     

Effect of metal doping into Ce0.5Zr0.5O2 on catalytic activity of MnOx/Ce0.5-xZr0.5-xM0.2xOy/Al2O3 for benzene combustion

The research investigated the effect of doping two metals separately or together into Ce0.5Zr0.5O2 on the catalytic activity of MnOx/Ce0.5–xZr0.5–xM0.2xOy/Al2O3 (M=Y, Mn, Y and Mn) for catalytic combustion of benzene. The prepared catalysts were characterized by X-ray diffraction (XRD), surface area analysis, oxygen storage capacity (OSC), and H2-temperature programmed reduction (H2-TPR). Cata-lytic test was performed on a conventional fixed bed flow reactor. The characterization results revealed that Y and Mn ions entered into the ceria-zirconia mixed oxides framework, which improved the textural properties and greatly promoted the MnOx dispersion on the support surface. The complete conversion temperature of benzene on MnOx/Ce0.4Zr0.4Y0.1Mn0.1Oy /Al2O3 was 563 K, and the selectivity of carbon dioxides was 99%. This catalyst could be applied in a wide range of GHSV and wide concentration condition, showing great potential for application.     

五氧化二钒的提取和氮化

根据广西某石煤矿的特点,采用氧化焙烧、酸性浸出、溶剂萃取、铵盐沉钒工艺得到了V2O5含量为99．3％的粉末状V2O5产品,为了进一步提高五氧化二钒的性价比,该试验以五氧化二钒为原料,炭黑为还原剂,采用微波法研究了氮化钒的制备工艺,产物氮含量为12．6％,经过XRD分析为纯相氮化钒。     

Low temperature selective catalytic reduction of NO by C3H6 over Ce Ox loaded on AC treated by HNO3

The activated carbons from coal were treated by HNO3(named as NAC) and used as carriers to load 7% Ce(named as Ce(0.07)/NAC) by impregnation method. The physical and chemical properties were investigated by thermogravimetric-differential thermal analysis(TG-DTA), Brunauer-Emmett-Teller(BET), X-ray diffraction(XRD), X-ray photoelectron spectra(XPS), scanning electron microscopy(SEM) and NH3-temperature programmed desorption(NH3-TPD) and NO-temperature programmed desorption techniques. The catalytic activities of Ce(0.07)/NAC were evaluated for the low temperature selective catalytic reduction(SCR) of NO with C3H6 using temperature-programmed reaction(TP-reaction) in NO, C3H6, O2 and N2 as a balance. The results showed that the specific surface area of Ce(0.07)/NAC was 850.8 m2/g and less than NAC, but Ce oxides could be dispersed highly on the activated carbons. Ce oxides could change acid sites and NO adsorption as well as oxygen-containing functional groups of activated carbons, and Ce4+ and Ce3+ coexisted in catalysts. The conversion of NO with C3H6 achieved 70% at 280 °C over Ce(0.07)/NAC, but with the increase of O2 concentration, heat accumulation and nonselective combustion were exacerbated, which could cause surface ashing and roughness, resulting in a sharp decrease of catalytic activities. The optimum O2 concentration used in the reaction system was 3% and achieved the high conversion of NO and the widest temperature window. The conversion of NO was closely related to the NO concentrations and [NO]/[C3H6] ratios, and the stoichiometric number was just close to 2:1, but the presence of H2 O could affect the denitration efficiency of catalyst.     

从含钒污泥渣中提取V2O5的工艺研究

含钒污泥渣（干基）中约含钒６～１５％，铬２～１９％，这种泥渣国内尚未见妥善处理办法。作者采用含钒污泥渣单独钠法焙烧提取，以及用含钒污泥渣与提机后的残渣混合纳法焙烧提钒，产生的Ｖ２Ｏ５符合沪Ｑ／ＹＢ５４１－８６技术条件。     

Preparation and Photocatalytic Property of Er_2O_3/TiO_2 Complex Photocatalyst

Preparation and Photocatalytic Property of Er_2O_3/TiO_2 Complex Photocatalyst     

Rare earths (Ce,Y, Pr) modified Pd/La_2O_3-ZrO_2-Al_2O_3 catalysts used in lean-burn natural gas fueled vehicles

14%REO_x-2.5%La_2 O_3-33.5%ZrO_2-50%Al_2 O_3(RE = Ce, Y, Pr) composites were prepared by a coprecipitation method. The Pd catalysts were obtained by an aqueous solution of Pd(NO_3)_2 loaded on the rare earths modified composites with an initial wet impregnated method. The experiment results show that catalytic activity of the rare earths modified Pd/La_2 O_3-ZrO_2-Al_2 O_3 catalysts is better than bare sample for methane oxidation. The structural characterization results reveal that the rare earths modified Pd catalysts increase amounts of surface active oxygen species by X-ray photoelectron spectroscopy(XPS) analysis and improve the dispersion of active component from H2-temperature programmed reduction(H2-TPR) measurement compared with bare sample. Especially,Pd/14%Y_2 O_3-2.5%La_2 O_3-33.5%ZrO_2-50%Al_2 O_3 sample exhibits highly active stability, it is related to the Pd particles highly dispersion,which was observed by transmission electron microscope(TEM) images.     

Effect of high temperature pretreatment on the thermal resistance properties of Pd/CeO_2/Al_2O_3 close-coupled catalysts

Fresh Pd/CeO_2/Al_2O_3 close coupled catalyst was prepared by the stepwise impregnation method and calcined at 550 °C for 3 h, which was then pretreated at 700, 800, and 900 °C for 3 h, respectively. Finally, these pretreated catalysts were aged at 1000 °C for 3 h to study their anti-aging properties. The catalytic activities of the catalysts were investigated detailedly, and the results showed that the catalyst pretreated at 800 °C before aging treatment possessed the best anti-aging performance for C_3H_8 oxidation. XRD and XPS results indicated that well-crystallized CeO_2 particles were formed during calcinations at 800 °C, which made CeO_2 an effective promoter. HRTEM revealed that Pd particles found on the edge of CeO_2 over the aged catalyst pretreated at 800 °C were relatively smaller than those over the catalysts without pretreatment. H_2-TPR and XPS results also implied that the interaction between well-crystallized CeO_2 and Pd suppressed the deactivation of PdO sites and further enhanced the catalytic performance.     

Novel mesoporous CeVWOx/TiO2 nanosheets for selective catalytic reduction of NO by NH3

Herein,we report the self-sacrificial template strategy to design mesoporous layered CeVWO_x/TiO₂ catalysts for the selective catalytic reduction of NO by NH₃（NH₃-SCR）.As-fabricated CeVWO_x/TiO₂ catalysts with unique mesoporous and layered structure were successfully prepared through the synthesis of Ce,Ti-MOFs by solvothermal method,the impregnation of vanadium and tungsten in Ce,Ti-MOFs and high temperature calcination process.As NH₃-SCR catalysts,well-designed CeVWO_x/TiO₂ catalysts exhibit excellent SCR activity with the NO_x conversion of over 90% between 210 and 470℃.Meanwhile,CeVWO_x/TiO₂ shows superior tolerance to water vapor and SO₂.The features of unique mesoporous layered nanostructure,surface acidity,tunable reducibility,active and the strong interaction of active metal oxide and support in CeVWO_x/TiO₂ nanosheets should contribute to the improved SCR performance.In situ diffuse reflection infrared Fourier transform spectroscopy（DRIFTS） analysis indicates that both Langmuir-Hinshelwood（L-H） and Eley-Rideal（E-R） mechanisms are present on the surface of CeVWO_x/TiO₂ at low temperature.This work offers a facile strategy to design and fabricate efficient 2D deNO_x catalyst.     

从西北某石煤钒矿中提取钒的试验研究

西北某石煤钒矿中V2O5质量分数为1．07％,研究了采用氧化焙烧-常温浸出-中和-还原-溶剂萃取-铵盐沉淀工艺提取V2O5。最佳条件下,钒浸出率大于85％,总回收率大于800,产品中V2O5质量分数大于98％,符合GB3283-1987冶金98质量标准。     

Influence of Al_2O_3/CeZrAl composition on the catalytic behavior of Pd/Rh catalyst

Al2O3 and Ce-Zr mixed oxides are important components of the automobile three-way catalyst.Various contents modifying A12O3(GAL) was physically introduced into Ce-Zr-Al mixed oxides(CZA) to form series of GAL/CZA composition.The Pd/Rh catalyst samples were prepared by different GAL/CZA support loading Pd/Rh,then aged at 950 oC for 6 h.The catalytic behavior of different Pd/Rh catalyst samples was studied.Surface area,oxygen storage capacity(OSC) and H2 adsorption capacity(TPR) of fresh and aged samples were...     

Preparation, Characterization and Photo-Catalytic Behavior of Y_2O_3/TiO_2 Composite Semiconductor Nanopowder

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