Effect of different doping elements on performance of Ce-Mn/TiO2 catalyst for low temperature denitration

Sm and Ho were doped in Ce-Mn/TiO₂ catalyst respectively to enhance its denitration performance at low temperature.X-ray diffraction(XRD),N₂ adsorption-desorption,X-ray photoelectron spectroscopy(XPS),NH₃-temperature programmed desorption(NH₃-TPD),H₂-temperature programmed reduction(H₂-TPR) and in situ diffuse reflectance infrared Fourier transform spectroscopy(DRIFTS) techniques were used to analyze the structure and performance ...     

Enhancement of potassium resistance of Ce-Ti oxide catalyst for NH3-SCR reaction by modification with holmium

Alkali metal K in exhaust gas has a deactivation effect on NH₃-SCR catalysts.In this work,it is discovered that the addition of Ho on CeTi catalyst can remarkably strengthen its K tolerance.The conclusions of Brunauer-Emmett-Teller(BET),X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS),NH₃ temperature programmed desorption(NH₃-TPD)and H₂temperature programmed reduction(H₂-TPR)analyses demonstrate that the enhancement of K resistance mainly originates from its stronger surface acidity and redox capability,the higher concentration of Ce³⁺species and surface chemisorbed oxygen.In situ DRIFT analysis reveals that the introduction of Ho on CeTi can remarkably improve the adsorption of NH₃ and NO_x species on catalyst surface,accompanied by the intensified reactivity of ad-NH₃ species,which should also administer to improve the K resistance.     

Roles of Lewis and Brnsted acid sites in NO reduction with ammonia on CeO_2-ZrO_2-NiO-SO_4~(2-) catalyst

Nickel and sulfate co-modified CeO2-ZrO2 catalysts were prepared by sol-gel method. The catalysts were characterized by XRD, FTIR, XPS, NH3 chemisorption and NH3-SCR activity tests. The results showed that the enhanced acidity of CeO2-ZrO2 catalysts by nickel and sulfate co-modification was responsible for the broadened temperature window and improved the selectivity to N2 in NH3-SCR deNOx. The introduction of nickel to CeO2-ZrO2 solid solutions resulted in more Ce3+ on surface of catalyst, leading to an in...     

Preferences for tastes paired with recovery from thiamine deficiency in rats: Appetitive conditioning or learned safety?

Conducted a study of 80 male Sprague-Dawley rats to investigate earlier findings that rats develop learned preferences for flavors paired with recovery from vitamin deficiencies. Results show that thiamine deficient Ss preferred flavors paired with recovery from deficiency to other familiar flavors, suggesting that part of the preference for flavors paired with recovery was the result of appetitive conditioning. Data are discussed in relation to "learned safety," specific hungers, illness-induced neophobia, and other phenomena in the taste-aversion literature. (16 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Structural and superconducting properties in Y0.6Gd0.4Ba2（Nb）Cu3O7-y cuprates doped with niobium

Polycrystalline YBa2Cu3O7-y (YBCO) and Y0.6Gd0.4Ba2-xNbxCu3O7-y (YGBNCO) compounds with 0≤x≤0.225 were synthesized using standard solid state reaction technique. The structure for all samples was characterized by X-ray difference (XRD) and scanning electron microscopy (SEM). The transport properties were measured by the (FPP) method in the temperature range from 70 to 130 K. As the Nb content in the samples increased, a diffused phase indicating a niobium perovskite phase and a small amount of unidentified phase appeared. With the increase of Nb content, the superconducting transition temperature Tconset increased slowly with x≤0.125, and then it remained unchanged or slowly decreased with 0.125≤x≤0.225. It could be found that there was a slow decrease of zero-resistance temperature, Tcoffset, with the increase of Nb content. The larger transition width might result from the YBa2NbO6 phase, impurity and unidentified phases of the sample due to the Nb doping.     

Ce(Ⅲ)-modulation over non-enzymatic Pt/CeO2/GO biosensor with outstanding sensitivity and stability for lactic acid detection

A series of non-enzymatic graphene functionalized biosensors was developed via deposition precipitation method for lactic acid(LA) detection,which we re characterized by transmission electron micro scopy(TEM),Raman spectroscopy,X-ray photoelectron spectroscopy(XPS),gas chromatography-mass spectrometry,liquid chromatography-mass spectro metry,and proton nuclear magnetic re sonance(¹H NMR).The electrochemical performances of the non-enzymatic biosensors were measured by means of the ele...     

Construction of bimetallic Pt-Pd/CeO2-ZrO2-La2O3 catalysts with different Pt/Pd ratios and its structure-activity correlations for three-way catalytic performance

A series of Pt-Pd bimetallic catalysts supported on CeO₂-ZrO₂-La₂O₃ mixed oxides were synthesized through the conventional impregnation method.Three-way catalytic performance evaluations along with detailed physio-chemical characterizations were carried out to establish possible structure-activity correlations.Results show that on the one hand,different Pt/Pd ratios can strongly affect the TWC behaviors of Pt-Pd/CZL catalysts by modulating the synergis...     

Selective catalytic reduction of NOx with NH3 over core-shell Ce@W catalyst

An environmentally benign WO₃ wrapped cubic CeO₂ core–shell catalyst (Ce@W) was developed for the selective catalytic reduction of NO_x with NH₃. Compared with CeW particles prepared via the conventional co-precipitation method, this core–shell catalyst not only displays higher tolerance to SO₂ and H₂O, but also exhibits a wider activity temperature window of 250–450 °C, in which NO_x conversion and N₂ selectivity reaches 100%. The improved performance of Ce@W catalysts can be contributed to the strong interactions between CeO₂ (100) and WO₃, which generates more Ce³⁺ and surface chemisorbed oxygen. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTs) reveal that the more thermally stable Brønsted acid sites on Ce@W lead to its excellent high-temperature activity.     

Revealing active species of CePO4 catalyst for selective catalytic reduction of NOx with NH3

Revealing the active species of the catalyst is conducive to the design of more efficient catalyst.Herein,we tried to demonstrate the roles of amorphous and crystalline structures on CePO₄ catalyst during selective catalytic reduction(SCR) of NO_x by NH₃.Higher calcination temperature promotes the transfer of amorphous structure to crystalline structure on the surface of CePO₄.Both amorphous and crystalline CePO₄ species on CePO-X samples can...     

A novel ceria hollow nanosphere catalyst for low temperature NOx storage

In this work, a highly active CeO₂ catalyst with hollow nanosphere morphology for low temperature NO_x storage was prepared by a surfactant-assisted solvothermal reaction. The physicochemical properties of ceria samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N₂ adsorption–desorption, H₂-temperature programmed reduction (H₂-TPR), X-ray photoelectron spectroscopy (XPS) and in situ diffused reflectance infrared Fourier transform spectroscopy (DRIFTS). The as-prepared CeO₂ nanosphere possesses excellent NO oxidation capacity, smaller mesopores, better reducibility and more surface Ce³⁺ content. Compared with CeO₂ with nanorod and nanoparticle morphologies, CeO₂ nanosphere shows better intrinsic low temperature NO_x trapping performance, with a wide operating temperature window (150–300 °C), high NO_x adsorption capacity (NAC, 640–745 μmol/g) and high NO_x storage capacity (NSC, 250–350 μmol/g). Two reaction pathways are speculated for NO_x adsorption on CeO₂ nanosphere, including “nitrate route” and “nitrite route”. The thermally unstable surface nitrites formed on the CeO₂ nanosphere allow ceria to release more NO_x during the desorption process. The present work provides a new ceria morphology for NO_x traps, which may become a potential excellent NO_x storage material.     

Sm-MnOx catalysts for low-temperature selective catalytic reduction of NOx with NH3: Effect of precipitation agent

A series of Sm-Mn mixed oxide catalysts were prepared via precipitation using various precipitants,namely Na₂CO₃(NH₄)₂CO₃,and NH₃·H₂O,and evaluated for the selective catalytic reduction(SCR) of NO_x with NH₃ at low temperatures.Various characterisation techniques were used to determine the physicochemical properties of the catalysts,and it is found that their catalytic performance is greatly influen...     

A-site defects in LaSrMnO_3 perovskite-based catalyst promoting NO_x storage and reduction for lean-burn exhausts

Herein,we report the high De-NO_x performance of the A-site defective perovskite-based Pd/La_(0.5)Sr_(0.3)MnO_3 catalyst.The formation of the defective perovskite structure can be proved by both the increased Mn~(4+)/Mn~(3+) ratio and serious lattice contraction due to cationic nonstoichiometry.It promotes the Sr doping into perovskite lattice and reduces the formation of the SrCO_3 phase.Our results demonstrate that below 300℃ the A-site defective perovskite can be more efficiently regenerated than the SrCO_3 phase as NO_x storage sites due to the latter's stronger basicity,and also exhibits the higher NO oxidation ability than the A-site stoichiometric and excessive catalysts.Both factors promote the lowtemperature De-NO_x activity of the Pd/La_(0.5)Sr_(0.3)MnO_3 catalyst through improving its NO_x trapping efficiency.Nevertheless,above 300℃,the NO_x reduction becomes the determinant of the De-NO_x activity of the perovskite-based catalysts.A-site defects can weaken the interactions between perovskite and Pd,inducing activation of Pd sites by in-situ transformation from PdO to metallic Pd in the alternative leanburn/fuel-rich atmospheric alternations,which boosts the De-NO_x activity of the Pd/La_(0.5)Sr_(0.3)MnO_3 catalyst.The Pd/L_(0.5)Sr_(0.3)MnO_3 catalyst exhibits the high sulfur tolerance as well.These findings provide insight into optimizing the structural properties and catalytic activities of the perovskite-based catalysts via tuning formulation,and have potential to be applied for various related catalyst systems.     

Er-modified MnOx for selective catalytic reduction of NOx with NH3 at low temperature: Promoting effect of erbium on catalytic performance

Various Er modified MnO_x catalysts were synthesized using co-precipitation approach and tested in the selective catalytic reduction of NO_x by ammonia(NH₃-SCR).Catalysts were analyzed with various characterization techniques,and it is found that the doping of Er can enormously enhance the catalytic performance of MnOx catalyst.MnEr_0.1 demonstrates advantageous catalytic performance in the NH₃-SCR reaction owing to rich surface acidic sites,hi...     

Extruded monolith MnOx-CeO2-TiO2 catalyst for NH3-SCR of low temperature flue gas from an industry boiler: Deactivation and recovery

The selective catalytic reduction(SCR) of NO_x with NH₃(NH₃-SCR) technology has been widely applied for reducing NO_x emissions from stationary and mobile sources.In this work,the extruded monolith MnO_x-CeO₂-TiO₂ catalyst was installed in a cement kiln for NH₃-SCR of NO_x,where the flue gas temperature was 110-140℃.It is found that the monolith catalyst is severely deactivated after operating for abou...     

Promotion effect of niobium on ceria catalyst for selective catalytic reduction of NO with NH3

The CeO₂, Ce–Nb–O_x and Nb₂O₅ catalysts were synthesized by citric acid method and the promotion effect of Nb on ceria for selective catalytic reduction (SCR) of NO with NH₃ was investigated. The catalytic activity measurements indicate that the mixed oxide Ce–Nb–O_x presents a higher SCR activity than the single oxide CeO₂ or Nb₂O₅ catalyst. In addition, the Ce–Nb–O_x catalyst shows high resistance towards H₂O and SO₂ at 280 °C. The Raman, X-ray photoelectron spectra and temperature programmed reduction with H₂ results indicate that the incorporation of Nb provides abundant oxygen vacancies for capturing more surface adsorbed oxygen, which provides a superior redox capability and accelerates the renewal of active sites. Furthermore, the Fourier transform infrared spectra and temperature programmed desorption of NH₃ results suggest that niobium pentoxide shows high surface acidity, which is partly retained in the Ce–Nb–O_x catalyst possessing a high content of Lewis and Brønsted acid sites. Therefore, the incorporation of Nb improves both the redox and acidic capacities of Ce–Nb–O_x catalyst for the SCR reaction. Here, the redox behavior is primarily taken on Ce and the acidity is well improved by Nb, so the synergistic effect should exist between Ce and Nb. In terms of the reaction mechanism, in situ DRIFT experiments suggest that both NH₃ on Lewis acid sites and NH₄⁺ on Brønsted acid sites can react with NO species, and adsorbed NO and NO₂ species can both be reduced by NH₃. In the SCR process, O₂ primarily acts as the accelerant to improve the redox and acid cycles and plays an important role. This work proves that the combination of redox and acidic properties of different constituents can be feasible for catalyst design to obtain a superior SCR performance.