Effects of ceria/zirconia ratio on properties of mixed CeO_2-ZrO_2-Al_2O_3 compound

A series of CexZr0.50-xAl0.50O1.75(0.05≤x≤0.45) mixed oxides with different Ce/Zr ratio were prepared by co-precipitation method and characterized by means of X-ray diffraction(XRD),Brunauer-Emmet Teller method(BET),temperature-programmed reduction(H2-TPR) and oxygen pulsing technique.The XRD results showed that all samples kept the single CeO2 cubic fluorite structure after calcination at 600 and 1000 oC for 5 h.The results of BET revealed that CexZr0.50-xAl0.50O1.75 with Ce/Zr molar ratio 1/1 exhibited higher specific surface area(212 m2/g) and larger pore volume(0.40 ml/g).For all aged samples,CZA with Ce/Zr molar ratio 3/7 presented the highest specific surface area(104 m2/g) and pore volume(0.34 ml/g).The compounds could still keep prominent structural and textural stability with excellent redox properties even calcined at 1000 oC.     

Catalytic oxidation of formaldehyde over CeO_2-Co_3O_4 catalysts

A series of CeO_2-Co_3O_4 mixed oxide catalysts with different Co/(Co+Ce) atomic ratios were synthesized by citric acid sol-gel method and used for catalytic oxidation of formaldehyde(HCHO). Many techniques such as Brumauer-Emmett-Teller(BET), X-ray diffraction(XRD), scanning electron microscopy(FE-SEM), temperature programmed reduction(H_2-TPR), temperature-programmed desorption(O_2-TPD) and X-ray photoelectron spectroscopy(XPS) were used to characterize catalysts. The results of catalytic performance tests showed that the catalyst CeO_2-Co_3O_4 with Co/(Co+Ce) ratio of 0.95 exhibited the best performance, and the temperature of complete oxidation of HCHO was 80 oC. The analytical results indicated that the addition of CeO_2 enhanced the specific surface area of Co_3O_4 and the fine dispersion of both of them. Moreover, the strong interaction between CeO_2 and Co_3O_4 resulted in the unique redox properties, which enhanced the available surface active oxygen and led to high valence state of cobalt oxide species. All those effects played crucial roles in the excellent performance of CeO_2-Co_3O_4 for the HCHO oxidation.     

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.     

Structure and oxygen storage capacity of Pd/Pr/CeO_2-ZrO_2 catalyst:effects of impregnated praseodymia

Praseodymium(Pr) was impregnated to CeO2-ZrO2 solid solution by an impregnation method.The as-obtained Pr modified CeO2-ZrO2 was impregnated with 1 wt.% Pd to prepare the catalysts.The structure and reducibility of the fresh and hydrothermally aged catalysts were characterized by X-ray diffraction(XRD),Raman,X-ray photoelectron spectroscopy(XPS),CO chemisorption and H2 temperature-programmed reduction(H2-TPR).The oxygen storage capacity(OSC) was evaluated with CO serving as probe gas.Effects of impregnated Pr on the structure and oxygen storage capacity of catalysts were investigated.The results showed that the aged Pr-impregnated samples had much higher OSC and better reducibility than the unmodified ones.The scheme of structural evolutions of the catalysts with and without Pr was also established.Partial of the impregnated Pr diffused into the bulk of CeO2-ZrO2 during ageing,which inhibited the sintering,and increased the amount of oxygen vacancies in CeO2-ZrO2 support.Furthermore,those impregnated Pr species which covered on the surface of the support obstructed the strong metal-support interaction between Pd and Ce so as to reduce the encapsulation of Pd as well as the back spill-over of the oxygen during the catalytic process.     

Characterization and photoluminescence of Lu_2O_3-Eu~（3＋） nano-phosphor prepared by modified solution combustion method

Nanoscale Lu2O3:Eu3+ phosphor was prepared by a modified solution combustion method using urea and acrylamide monomer.The particle sizes and photoluminescent properties of nano-phosphor were closely related to the molar ratio of urea-to-RE nitrates and acrylamide monomer-to-RE nitrates.The as-prepared samples with the sizes of 9.6-11.6 nm were characterized by X-ray diffraction,scanning electron microscopy,transmission electron microscopy and energy dispersive spectrometer.Lu2O3:Eu3+ nano-phosphor that depicted high photoluminescence in the size around 10 nm was reported.Compared with the sample prepared by solid state reaction,the photoluminescence of sample was increased sufficiently to be 45.1%.The emission spectra of the samples presented the typical emission from 5D0 level to 7FJ(J=0,1,2,3,4) level of the Eu3+ ion.     

Effect of CeO_2 on Crystal Structures and Catalytic Properties of the Mn_2O_3 Catalysts

ＥｆｆｅｃｔｏｆＣｅＯ_２ｏｎＣｒｙｓｔａｌＳｔｒｕｃｔｕｒｅｓａｎｄＣａｔａｌｙｔｉｃＰｒｏｐｅｒｔｉｅｓｏｆｔｈｅＭｎ_２Ｏ_３ＣａｔａｌｙｓｔｓＬｕｏＭｅｎｇ－Ｆｅｉ（罗孟飞）；ＺｈｕＢｏ（朱波）；ＹｕａｎＸｉａｎ－Ｘｉｎ（袁贤鑫）（Ｃａｔａｌｙ...     

Novel 3D porous graphene decorated with Co_3O_4/CeO_2 for high performance supercapacitor power cell

Tremendous research efforts have been aimed at ever-increasing worldwide energy demand. For this purpose, the hybrid supercapacitor power cell were prepared composing 3D porous graphene decorated with Co_3O_4-CeO_2 nano-particles herein by using flower stem as biotemplate. The resulting samples were characterized by field emission scanning electron microscopy(FESEM), transmission electron microscopy(TEM), Raman spectra, X-ray diffraction spectroscopy(XRD), nitrogen adsorption and desorption, X-ray photoelectron spectrogram(XPS), and electrochemical test. The 3D graphene acted as an excellent carrier together with Co_3O_4-CeO_2 nano-particles, boosting the specific capacitance of composite(221 F/g), which exceeded the theoretical value limit. This facile biotemplate method of research provided an eco-friendly and cut-price route to obtain high-quality graphene and Co_3O_4-CeO_2nano-composites owing to the unique porous structure derived from original template(flower stem). The finding presented a simple strategy for fabrication of novel energy storage devices.     

CeO_2对Mo/Al_2O_3复合材料微观结构的影响

采用无压烧结法制备含CeO2的Mo/Al2O3材料,用MM-200型环-块式摩擦磨损试验机测试该材料在滑动干摩擦条件下的磨损行为,通过X射线衍射(XRD)和电子探针对其微观结构和磨损后的形貌进行研究和分析。结果表明,添加CeO2的烧结样品中出现CeAl11O18相,且随CeO2含量(体积分数)增加,CeAl11O18逐渐增多,Al2O3相应减少。当CeO2的体积分数为6%时Al2O3全部由CeAl11O18取代;CeO2的添加使Al2O3和CeAl11O18相边界处均呈现圆钝形貌,并且存在Mo、Al、O的相互扩散区域。磨损形貌表明,1 730℃烧结的样品中出现摩擦转移层,当CeO2含量达到4%时,该摩擦转移层大量出现,从而改善材料的耐磨性。     

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.     

Enhanced photocatalytic activity of Gd~(3+) doped TiO_2 and Gd_2O_3 modified TiO_2 prepared via ball milling method

Gd~(3+)/TiO_2 and Gd_2O_3/TiO_2 nanoparticles were prepared by ball milling method.The effects of Gd~(3+)ion and Gd_2O_3 on the structure and optical property of TiO_2 were studied by XRD and UV-vis DRS.Specific surface area was determined by Brunauer-Emmett-Teller(BET)method.The morphology and elemental composition were characterized by SEM-EDS.XPS was used to determine the surface compositions and chemical character of elements.The sample sizes and microstructures were observed by TEM.The photocatalytic activities of TiO_2 nanoparticles modified with rare earth metal gadolinium(Gd~(3+)ion or Gd_2O_3)were evaluated by degradation of methylene blue(MB)under UV light.Experimental results indicate that 2,5 mol%Gd~(3+)/TiO_2 shows the best photocatalytic activity compared with Gd_2O_3/TiO_2 and pure TiO_2.The existence of gadolinium can exhibit the aggregation and induce lattice distortion of TiO_2 obtained from XRD,SEM and TEM results.The band gap energy of 2.5 mol%Gd~(3+)/TiO_2 decreases to3.07 eV and it leads to visible light absorption response which can be seen from UV-vis absorption spectra.The surface area of 2.5 mol%Gd~(3+)/TiO_2 equals to 85.8 m~2/g and average crystal size is 21.1 nm.EDS and XPS analyses reveal that gadolinium can be introduced either into TiO_2 lattice or adsorbed on the surface of TiO_2.The content of surface OH groups in 2.5 mol%Gd~(3+)/TiO_2 is 50,88%(1.55 times higher than that of pure TiO_2)and the content of lattice oxygen decreases to 11.26%.The MB(25 mg/L)degradation reaction rate constants of 2,5 mol%Gd~(3+)/TiO_2,0.5 mol%Gd_2O_3/TiO_2 and pure TiO_2 were0.0713,0.0588 and 0.0263 min~(-1),respectively.The degradation rates of rhodamine B(30 mg/L)in 60 min are 97,9%,90.1%and 84.6%for 2,5 mol%Gd~(3+)/TiO_2,0.5 mol%Gd_2O_3/TiO_2 and pure TiO_2,respectively.     

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.     

Effects of Y_2O_3/Y on Si-B co-deposition coating prepared through HAPC method on pure molybdenum

In order to clarify the effects of reactive element Y on the properties of Si-B co-deposition coating on Mo substrate,the Si-B-Y_2O_3 and Si-B-Y co-deposition coatings were prepared at 1300°C for 5 h by using the pack mixtures 16Si-4B-xY_2O_3/Y-4NaF-(76–x)Al_2O_3(wt.%,x=0,0.5,1,2,4,8).X-ray diffraction(XRD),energy dispersive spectroscopy(EDS) and wavelength dispersive spectroscopy(WDS) techniques were used to analyze the structure and oxidation behavior of these coatings.The results revealed that the Si-B-Y_2O_3 and Si-B-Y co-deposition coatings had the same structure with that of the Si-B co-deposition coating.However,Y was incorporated into these coatings and the thicknesses of these coatings were thicker than that of the Si-B co-deposition coating.In addition,the Si-B-Y co-deposition coating demonstrated better cyclic oxidation resistance than the Si-B co-deposition coating at 1100 °C.The modifying mechanism of Y on the Si-B co-deposition coating was discussed.     

Promoting effect of microwave irradiation on CeO_2-TiO_2 catalyst for selective catalytic reduction of NO by NH_3

In this work we prepared several CeO₂-TiO₂ catalysts for the NH₃-SCR reactionusing co-precipitation with assistance of microwave irradiation. The catalytic NH₃-SCR activities over CeO₂-TiO₂ catalysts at low temperatures are largely enhanced by the treatment of microwave irradiation, the operation temperature window is also broadened. For better understanding the promotion mechanism, the catalyst prepared by conventional co-precipitation with and without microwave irradiation treatment was characterized with H₂-TPR, NH₃-TPD, XPS, XRD and BET. Microwave irradiation treatment accelerates the crystallite rate of CeO₂-TiO₂ catalysts, and greatly enlarges their surface area by adjusting their microstructures. The resistance to SO₂ and H₂O is also improved via regulating the hierarchical pore structure by the microwave irradiation. Microwave irradiation treatment can also improve the redox property and increase the acid sites over the catalyst surfaces. The result of in situ DRIFTS suggests that the microwave irradiation treatment generates more Brønsted acid sites on CeO₂-TiO₂-2 h catalyst, helpful in SCR reactions. XPS results show that after microwave irradiation on the CeO₂-TiO₂ catalysts, the surface demonstrates an elevated concentration of chemisorbed oxygen, consequently leading to better oxidation of NO to NO₂. Additionally, the molar ratio of Ce³⁺/Ce⁴⁺ has been elevated after being treated by microwave irradiation, a vital factor in enhancing the NH₃-SCR activities.     

Synthesis of CeO_2/fly ash cenospheres composites as novel photocatalysts by modified pyrolysis process

A novel fly ash cenospheres(FACs)-supported CeO2 composite(CeO2/FACs) was successfully synthesized by the modified pyrolysis process.The prepared composites were characterized by X-ray diffraction(XRD), scanning electron microscopy(SEM), X-ray photoelectron spectroscopy(XPS), and diffuse reflection spectra(DRS) techniques.XRD results indicated that the CeO2 film coated on cenospheres was a face-centered cubic structure.SEM images confirmed that the CeO2 film was relatively compact.XPS results showed that Ce was present as both Ce4+ and Ce3+ oxidation states in CeO2 film coated on FACs substrate.The bandgap of the composite was narrower compared with the pure CeO2.The as-prepared material exhibited good photocatalytic activity for the decolorization of methylene blue(MB) under visible light irradiation, and the first-order reaction rate constant(k) of 0.0028 min–1 for CeO2/FACs composite was higher than 0.0015 min–1 of pure CeO2.The fact that they floated on water meant that CeO2/FACs composites were easily recovered from water by filtration after the reaction.The recycling test revealed that the composites were quite stable during the MB photocatalytic decolorization.The CeO2/ FACs catalyst was therefore promising for practical use in the degradation of pollutants or water cleanup.     

Fabrication of a flower-like Pd/CeO2 material with improved three-way catalytic performance

Pd/CeO2 catalysts with flower-like morphology were fabricated via an ultrasonic-assisted membrane reduction (UAMR) and hydrothermal methods. The catalysts were physically characterized and evaluated fo...     

Ln_2O_3/ZrO_2催化合成DOP、DOM和DOA

采用共沉淀 -焙烧法制成的Ln2 O3 /ZrO2 (Ln =Nd、Sm、Er)担载型催化剂 ,由于比表面增大 ,分散性好 ,在催化合成DOP、DOM和DOA中效果明显 ,且Ln2 O3 的用量比用纯Ln2 O3 催化剂下降 60 %左右。     

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...     

Reduction of Tb~(4+) ions in luminescent Y_2O_3:Tb nanorods prepared by microwave hydrothermal method

Terbium doped yttrium oxide was prepared with the microwave hydrothermal method. The Y_2O_3:Tb nanomaterial crystallized as needle-like grains. Bright luminescence in the green region was observed. Significant luminescence intensity increase was obtained after thermal treatment. Reduction of terbium ions was observed after heating in the air atmosphere. Tb~(4+) ions were found to be stabilized by crystal impurities. Hydroxyl species were found to have impact on vacancies elimination. The terbium ions were used as optical and magnetic indicator of the material properties.     

Support interaction of Pt/CeO_2 and Pt/SiC catalysts prepared by nano platinum colloid deposition for CO oxidation

The interaction between Pt and its various supports can regulate the intrinsic electronic structure of Pt particles and their catalytic performance.Herein,Pt/CeO_2 and Pt/SiC catalysts were successfully prepared via a facile Pt colloidal particle deposition method,and their catalytic performance in CO oxidation was investigated.XRD,TEM,XPS and H_2-TPR were used to identify the states of Pt particles on the support surface,as well as their effect on the performance of the catalysts.Formation of the Pt-O-Ce interaction is one of the factors controlling catalyst activity.Under the oxidative treatment at low temperature,the Pt-O-Ce interaction plays an important role in improving the catalytic activity.After calcining at high temperature,enhanced Pt-O-Ce interaction results in the absence of metallic Pt~0 on the support surface,as evidenced by the appearance of Pt~(2+) species.It is consistent with the XPS data of Pt/CeO_2,and is the main reason behind the deactivation of the catalyst.By contrast,either no interaction is formed between Pt and SiC or Pt nanoparticles remain in the metallic Pt~0 state on the SiC surface even after aging at 800℃in an oxidizing atmosphere.Thus,the Pt/SiC shows better thermal stability than Pt/CeO_2.The interaction between Pt and the active support may be concluded to be essential for CO oxidation at low temperature,but strong interactions may induce serious deactivation of 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.