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.     

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.     

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.     

Effects of water on CO catalytic oxidation over Pd/CeO_2

The role of water in CO oxidation was investigated on Pd/CeO_2 with different morphologies(rods(R),cubes(C) and octahedrons(O)).Compared with the absence of water,CO oxidation activity increases 2 times in the presence of water on Pd/CeO_2-C;but a decrease is found on Pd/CeO_2-R.Catalyst characterization reveals that Pd is mainly in the form of solid solution(Pd_xCe_(1-x)O_(2-σ)) on Pd/CeO_2-R and a mixture of metal and Pd_xCe_(1-x)O_(2-σ) solid solution on Pd/CeO_2-C.The strong interaction between Pd and CeO_2-R results in the form of stable bidentate carbonates species;while the relatively weak interaction between Pd and CeO_2-C leads to the produce of unstable monodentate carbonates species.The effects of water on CO oxidation activity closely relate with the Pd chemical state and the types of carbonates species.Water restrains CO adsorption on Pd_xCe_(1-x)O_(2-σ) solid solution,but it has negligent effects on metallic Pd species.In the presence of water,bidentate carbonates species remains stable but the decrease in the amount of monodentate carbonates species is observed.     

From nanoparticles to single atoms for Pt/CeO_2:Synthetic strategies,characterizations and applications

Pt/CeO₂ catalysts with unitary Pt species,nanoparticles,clusters or single atoms,often exhibit excellent activity and unique selectivity in many catalytic reactions benefiting from their small size,abundant unsaturated active sites,and unique electro nic structure.In recent years,a tre mendous number of related articles have provided great inspiration to future research and development of Pt/CeO₂ catalysts.In this review,the state-of-the-art evolution of Pt nanoparticles to...     

High activity of CeO_2-TiO_2 composites for deep oxidation of 1,2-dichloroethane

CeO_2-TiO_2 catalysts prepared by different methods were investigated for deep oxidation of 1,2-dichloroethane(DCE),as a typical representative of the chlorinated volatile organic compounds(CVOCs).Characterization analysis reveals that CeO_2-TiO_2 catalysts prepared by sol-gel and coprecipitation methods exhibit higher specific area,CeO_2 and TiO_2 particles are highly dispersed into each other and the reducibility and mobility of active oxygen species are obviously promoted due to the strong interaction between the two catalysts CeO_2 and TiO_2,resulting in higher catalytic activity for DCE oxidation to and less chlorinated byproduct.The high calcination temperature would lead to the formation of a new monoclinic phase Ce_(0.3)Ti_(0.7)O_2 and sintering,which is the main reason for the catalytic activity for DCE oxidation markedly decreases.     

CeO_2/CuO catalysts using different template agent for preferential CO oxidation in H_2-rich stream

The CeO_2/CuO catalysts using different template agent(F68 L64, F127 and P123) were synthesized by the simple template and impregnation method. They were characterized by FESEM, XRD, N2 physisorption and H2-TPR techniques. It is found that the CeO_2/CuO catalysts are double pore distribution, and CeO_2 can enter into the gap of CuO supports and form the contact interface of copper and cerium. Among the asprepared catalysts, the CeO_2/CuO-F127 catalyst displays better activity at lower temperature and the CeO_2/CuO-P123 catalyst presents higher activity at higher temperature. The CeO_2/CuO-P123 catalyst has the smallest crystallite sizes of CuO and CeO_2 as well as the largest size of cubes, which may improve the interaction of copper and cerium and enhance the performance of CO oxidation.     

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。     

活性炭载体的超声波处理对Pt／C催化剂活性的影响分析

通过对活性炭载体进行不同条件的超声波处理获得了具有不同表面化学性质的载体，使用比表面积（BET）、酸碱滴定等技术手段对载体的物理化学性质进行了表征。将经过超声波处理的活性炭载体制备成Pt／C催化剂，并将催化剂直接用于催化反应，考察了活性炭载体的不同超声波处理条件对Pt／C催化剂性能的影响。实验发现，活性炭载体经过超声波处理后，表面灰分含量、pH值和中孔孔容有较大的变化；使用经过60min超声波处理后中孔孔容较大的活性炭作为载体制备的Pt／C催化剂，在催化加氢反应性能测试中显示了最高的催化活性。在此基础上，就活性炭载体的超声波处理对Pt／C催化剂活性的影响进行了讨论。     

Effects of loading transition metal(Mn,Cr,Fe,Cu) oxides on oxygen storage/release properties of CeO_2-ZrO_2 solid solution

Cerium zirconium-based(CZ) oxygen storage materials(OSMs) play a crucial role in three-way catalysts(TWCs),while CZ needs to be modified to satisfy more rigorous emission standard.In this study,transition metal(TMs=Mn,Cr,Fe,Cu) oxides modified CZ were prepared by incipient wetness impregnation method to improve the oxygen storage capacity of CZ-based materials.To clearly illustrate the influence of TM oxides,N₂ adsorption-desorption,X-ray diffraction(XRD),oxygen storage capacity(OSC),...     

Effect of synthesis time on morphology of CeO_2 nanoparticles and Au/CeO_2 and their activity in oxidative steam reforming of methanol

Ceria(CeO_2)supports,synthesized by hydrothermal treatment with different synthesis time(CeO_2-X h,where X is the synthesis time in h)in the presence of the surfactant cetyltrimethyl ammonium bromide,were used as supports for gold(Au)catalysts.The synthesis time significantly affects the morphological structure and crystallite size of CeO_2,where CeO_2-2 h has the smallest crystallite size with coexisting nanorods and nanoparticles.Transmission electron microscopy analysis confirms the morphology of CeO_2 with distinctive(110),(100)and(111)planes,in agreement with interplanar spacings of 0.19,0,27 and 0.31,respectively.However,the morphology of CeO_2-8 h and CeO_2-48 h is mainly a truncated octahedral with crystal planes(111)and(100)accompanied by an interplanar spacing of 0.31 and0.27 nm,respectively.The CeO_2-X h supports and those with a 3 wt%Au loading(Au/CeO_2-X h)were investigated in the oxidative steam reforming of methanol at temperatures between 200 and 400 ℃.The Au/CeO_2-2 h gave the highest methanol conversion level and hydrogen yield at a low temperature of 250 ℃.This superior catalytic performance results from the good interaction between the metal and support and the well-distributed Au species on the CeO_2 support.     

直接甲醇燃料电池Pt／C催化剂对甲醇的电催化氧化研究

通过循环伏安法研究了Pt/C催化剂对甲醇的电催化氧化活性,详细地考察了甲醇浓度、温度、介质以及酸度等电化学体系因素对Pt/C催化剂活性的影响。结果表明,上述四个电化学体系因素对Pt/C催化剂活性存在着明显的影响。甲醇浓度和温度的增加可以显著降低工作电极内阻,增加电极反应速率,提高Pt/C催化剂活性。改善溶液介质和控制适宜的酸度有利于Pt/C催化剂活性的提高。在本实验条件下,其最佳的运行工艺参数为:溶液介质为二次去离子水,酸度为1.0 mol/L H2SO4。     

Catalytic performance of a Pt-Rh/CeO_2-ZrO_2-La_2O_3-Nd_2O_3 three-way compress nature gas catalyst prepared by a modified double-solvent method

A Pt-Rh three-way catalyst(M-DS) supported on CeO_2-ZrO_2-La_2O_3-Nd_2O_3 and its analogous supported catalyst(DS) were developed via a modified double-solvent method and conventional double-solvent method, respectively. The as-prepared catalysts were characterized by N_2 adsorption-desorption, X-ray diffraction(XRD), CO-chemisorption, X-ray photoelectron spectroscopy(XPS) and hydrogen temperature-programmed reduction(H_2-TPR). The preformed Pt nanoparticles generated using ethanol as a reducing agent on M-DS presented enhanced Pt dispersion regardless of aging treatment as confirmed by XRD and CO-chemisorption measurements. The textural properties and reduction ability of M-DS were maintained to a large extent after aging treatment. This result was consistent with those of the N_2 adsorption-desorption and H_2-TPR, respectively. Meanwhile, the XPS analysis demonstrated that higher Pt~0 species and larger Ce~(3+) concentration could be obtained for M-DS. In the conversion of a simulated compressed natural gas(CNG) vehicle exhaust, both fresh and aged M-DS showed a significant enhancement in the activity and N_2-selectivity. Particularly, the complete conversion temperature(T_(90)) of CH_4 over the aged M-DS catalyst was 65 oC lower than that over the aged catalyst by conventional double-solvent method.     

CeO_2包覆对TiO_2传感器材料的氧敏性能的影响

针对CeO2 具有良好的催化性和稳定性 ,以及TiO2 具有优良的氧敏特性 ,采用溶胶 凝胶法制备CeO2 包覆TiO2 材料 ,并在自行设计的实验装置中对材料进行氧敏测试。该材料的温度系数低于纯TiO2 材料 ,且氧敏性能比纯TiO2 材料显著提高。其原因在于壳层中CeO2 颗粒为氧离子进出包覆体内的TiO2 提供通道 ,并利用CeO2 储、放氧能力 ,促进TiO2 电导率变化。     

Effect of interaction between different CeO2 plane and platinum nanoparticles on catalytic activity of Pt/CeO2 in toluene oxidation

The plane exposure of support vitally affects the catalytic performance of the catalyst. In this work, CeO₂ nanorods ((110) plane exposure), nano-octahedrons ((111) plane exposure) and nano-cubes ((100) plane exposure) were prepared as the supports of Pt/CeO₂ samples to investigate the effect of CeO₂ plane exposure on total toluene oxidation. Characterizations reveal that the (110) plane of CeO₂ is more helpful to the dispersion of Pt species, followed by (111) face. The improved dispersion of Pt species can enhance the metal-supports interaction, which promotes the electron transfer of CeO₂ carrier to Pt nanoparticles and the adsorption-activation of O₂, thereby facilitating the total oxidation of toluene via the Langmuir–Hinshelwood (L-H) mechanism. Therefore, Pt/CeO₂-r (nanorods) sample expresses excellent catalytic performance of toluene oxidation. Finally, the procedure of toluene total oxidation was studied by in-situ diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. We expect that this work can contribute to the development of an effective sample for the decomposition of volatile organic compounds (VOCs).     

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.     

Modified-EISA synthesis of mesoporous high surface area CeO_2 and catalytic property for CO oxidation

Mesoporous CeO2 particles with high surface area were synthesized using a modified evaporation-induced self assembly(EISA) method which combined citric acid as complexing agent.As-prepared powder and further thermal treatment samples were characterized by X-ray diffraction(XRD),transmission electron microscopy(TEM),selected area electron diffraction(SAED),Fourier transform infrared spectrometer(FTIR),thermogravimetry and differential thermal analysis(TG-DTA),Brunauer-Emmett-Teller(BET) and Barrett-Joyner-Ha...     

Influence of CeO_2 loading on structure and catalytic activity for NH_3-SCR over TiO_2-supported CeO_2

A series of supported CeO_2/TiO_2 catalysts were prepared to explore the influence of CeO_2 loading on these catalysts for the selective catalytic reduction of NO_3 by NH_3(NH_3-SCR).The catalysts were investigated in detail by means of XRD,Raman,H_2-TPR,NH_3-TPD,XPS,in situ DRIFTS,and NH3-SCR reaction.The activity of the catalyst is closely related to the content of CeO_2.When the loading of CeO_2 is near the dispersion capacity(1.16 mmol Ce~(4+)/100 m~2 TiO_2),the catalytic activity is better.This may be because that the dispersed CeO_2 is the active species and the catalyst has appropriate redox property,along with the larger amounts of surface Ce content and surface adsorbed oxygen species.Finally,a possible reaction mechanism via the Langmuir-Hinshelwood(L-H) mechanism is tentatively proposed to further understand the NH_3-SCR reaction.     

电化学活化条件对Pt/C催化剂甲醇电氧化催化活性的影响

利用亚硫酸路线和亚锡酸法合成了两种Pt/C催化剂,并利用循环伏安技术,详细地研究了循环伏安高电位和活化方式对Pt/C催化剂的甲醇电氧化催化活性的影响.研究结果表明:在改变高电位的逐步循环伏安活化方式下,不同的Pt/C催化剂的活化存在有不同的最优循环伏安高电位;在最优高电位下,一次性活化方式对亚锡酸法Pt/C催化剂的活化最为有效.不同的活化条件产生不同的催化活性,主要原因在于不同的活化过程形成的最终的Pt的存在形式不一样,致使催化剂对水和阴离子具有不同的吸附能力和吸附速率.     

Mesoporous CeO_2-C hybrid spheres as efficient support for platinum nanoparticles towards methanol electrocatalytic oxidation

The development of direct methanol fuel cells(DMFCs) is partially limited by the poor kinetics of methanol oxidation reaction(MOR) at the anode side.It was reported that the interaction between Pt and CeO_2 enhances the electrocatalytic performance of Pt catalyst for MOR.In this work,a hybrid material(CeO_2-C) composed of CeO_2 and carbon was successfully prepared by a simple hydrothermal method followed by calcination in inert atmosphere.The hierarchically porous nanostructure and especially good electronic conductivity of CeO_2-C make it an excellent support for Pt particles for application in electrocatalytic process.TEM investigation reveals that triple-phase interface of Pt,carbon and CeO_2 forms in Pt/CeO_2-C catalyst.Performance of the as-prepared catalyst for MOR was studied in alkaline medium.The Pt/CeO_2-C catalyst shows superior catalytic performance for MOR compared with Pt/CeO_2 and the physical mixture of Pt/CeO_2 and acetylene black(Pt/CeO_2+C).The significantly improved performance can be attributed to the synergetic effect between Pt particles and CeO_2-C support,and the better conductivity of CeO_2-C.This study provides a possible method to expand the application potential of CeO_2 materials in MOR,and may also be used in other electrocatalytic process.