Experimental and theoretical studies of carbon monoxide oxidation over W/Cu/Ce trimetallic oxides: the effect of W addition

It is a significant method to prepare highly dispersed polymetallic oxides using in-situ doping metal organic frameworks as precursors. Herein, a series of straw-like W/Cu/Ce trimetallic oxides were prepared by using phosphotungstic ionic liquid@Ce-based metal organic framework adsorbing with copper acetylacetonate as precursors. The effect of W content on catalytic activity of W/Cu/Ce trimetallic oxides for carbon monoxide (CO) oxidation was well-investigated. Comprehensive characterization methods and density functional theory calculations were adopted to reveal the property changes of Cu/CeO₂ catalyst by the addition of W. The results demonstrated that W, Cu, and Ce are highly dispersed in the prepared W/Cu/Ce trimetallic oxides, and adding proper amount of W can improve the activity of the catalyst. H₂ temperature-program reduction profiles, X-ray photoelectron spectroscopy, in-situ diffuse reflectance infrared Fourier transform spectroscopy, and density functional theory calculations clearly revealed that after the addition of W, the strength of Ce-O bond is weakened, the oxygen vacancy is increased, and the adsorption of CO is enhanced, respectively, which are vital reasons for its high catalytic activity. In addition, the CO oxidation reaction pathway over prepared W/Cu/Ce trimetallic oxides based on the Mars-van Krevelen mechanism was studied, and the results exhibited that CO can wrest the lattice oxygen of W/Cu/Ce trimetallic oxides to form CO₂, which is also proved to be the rate-determining step in reaction process.     

Unusual physical and chemical properties of Cu in Ce(1-x)Cu(x)O(2) oxides

The structural and electronic properties of Ce(1-x)Cu(x)O(2) nano systems prepared by a reverse microemulsion method were characterized with synchrotron-based X-ray diffraction, X-ray absorption spectroscopy, Raman spectroscopy, and density functional calculations. The Cu atoms embedded in ceria had an oxidation state higher than those of the cations in Cu(2)O or CuO. The lattice of the Ce(1)(-x)Cu(x)O(2) systems still adopted a fluorite-type structure, but it was highly distorted with multiple cation-oxygen distances with respect to the single cation-oxygen bond distance seen in pure ceria. The doping of CeO(2) with copper introduced a large strain into the oxide lattice and favored the formation of O vacancies, leading to a Ce(1-x)Cu(x)O(2-y) stoichiometry for our materials. Cu approached the planar geometry characteristic of Cu(II) oxides, but with a strongly perturbed local order. The chemical activities of the Ce(1-x)Cu(x)O(2) nanoparticles were tested using the reactions with H(2) and O(2) as probes. During the reduction in hydrogen, an induction time was observed and became shorter after raising the reaction temperature. The fraction of copper that could be reduced in the Ce(1-x)Cu(x)O(2) oxides also depended strongly on the reaction temperature. A comparison with data for the reduction of pure copper oxides indicated that the copper embedded in ceria was much more difficult to reduce. The reduction of the Ce(1-x)Cu(x)O(2) nanoparticles was rather reversible, without the generation of a significant amount of CuO or Cu(2)O phases during reoxidation. This reversible process demonstrates the unusual structural and chemical properties of the Cu-doped ceria materials.     

CO催化氧化中氧化铜对CeO2的调变作用

采用柠檬酸络合法制备并应用XRD、ICP和微反活性等方法研究了Cu－Ce－O催化剂体系,当体系中铜含量较少,焙烧温度较低时,以萤石矿型结构存在,CuO掺杂进入CeO2的晶格中;当铜含量较多,焙烧温度较高时,除了以萤石矿型结构存在外,还伴随有单斜晶系CuO的生成,焙烧温度高达1000℃时,体系无其它结构型式的晶相形成,研究发现少量的CuO使体系催化氧化CO的活性大大提高;只有极少量的CuO进入CeO2的晶格内部,该催化剂最佳配方是Cu／（Cu＋Ce）原子百分比为15％,700℃焙烧4h,其中起高催化氧化作用的是由CuO掺杂调变而成的萤石矿型复合氧化物,其组成为Cu0.06Ce0.94O1.94。     

铈铬比例对CeO2-CrOx复合氧化物催化剂上1,2-二氯乙烷催化氧化性能的影响

采用共沉淀法制备了不同铈铬比例的CeO₂-CrO_x复合氧化物(Ce/Cr 摩尔比分别为9/1、4/1、2/1、1/1、1/2、1/4、1/8)以及单纯的CeO₂和Cr₂O₃, 并研究了各催化剂对1,2-二氯乙烷(DCE)的催化氧化性能. 结果表明,相较于单纯的CeO₂, 不同铈铬比例的复合氧化物催化剂对DCE的催化氧化活性有明显提高, 其中Ce/Cr 摩尔比为2/1的CeO₂-CrO_x复合氧化物上DCE的氧化活性最好, 且只有极微量的含氯等副产物产生; 随着Ce/Cr 摩尔比减小, 对HCl的选择性有下降的趋势. 通过X射线衍射(XRD)、N₂吸附/脱附(BET)、紫外拉曼(UV-Raman)光谱、H₂程序升温还原(H₂-TPR)、NH₃程序升温脱附(NH₃-TPD)等实验技术, 研究了铈铬比例对铈铬复合氧化物的物理化学性质的影响. 结果表明, 适当比例Ce-Cr的复合, 形成了结构较稳定的Ce-Cr-O固溶体, 提高了催化剂活性氧物种的流动性, 催化剂表面酸量及强弱酸比例, 从而有利于DCE的吸附活化, 进一步脱氯降解以及深度氧化.     

Ce_(1-x)Fe_xO_2复合氧化物的结构及其催化碳烟低温燃烧性能

用水热法制备了不同摩尔比的系列Ce1-xFexO2复合氧化物碳烟燃烧催化剂.采用X射线粉末衍射(XRD)、比表面积(BET)、拉曼光谱(Raman)、H2程序升温还原(H2-TPR)及程序升温氧化反应(TPO)等技术考察了Fe含量对催化剂结构和性能的影响,重点探讨了催化剂表面性质和体相结构与催化活性和稳定性之间的关系.结果表明,Fe3+较难进入CeO2晶格中,部分Fe2O3分散在CeO2表面.铈铁固溶体(氧空位)有利于氧的吸附活化,而表面氧化铁对提高催化剂的抗老化能力起着重要作用.Ce0.8Fe0.2O2有最高的Fe3+掺杂量,有良好分散性的表面Fe2O3,显示出最好的催化活性和稳定性,催化碳烟的起燃温度(Ti)和生成CO2的峰值温度(Tp)分别为262和314℃.Ce0.8Fe0.2O2高温老化后的Ti和Tp仍较低,分别为292和392℃.     

Ce掺杂对碳纳米管负载Mn催化剂结构及SCR反应性能的影响

采用等体积浸渍法制备多壁碳纳米管(MWCNTs)负载Ce-Mn的催化剂,考察了Ce掺杂对Mn/MWCNTs催化剂上NH₃选择性催化还原(SCR)NO_x反应活性的影响.并运用透射电镜扫描、N₂吸附-脱附、程序升温还原、X射线光电子能谱、X射线衍射等手段,重点考察了Ce掺杂对Mn/MWCNTs催化剂结构性质的影响.结果表明,Ce掺杂能显著提高催化剂的SCR活性,其活性增量随着Ce含量的增加先增大后减小;当Ce/Mn为0.6时,催化剂活性最佳.表征结果显示,Mn/MWCNTs中添加Ce后,金属氧化物在MWCNTs上的分散程度提高;催化剂的比表面积和孔体积增大,平均孔径减小;氧化能力提高;表面氧含量增加,Mn化合价升高;结晶度降低,Mn主要以无定形或微晶形式存在,Ce主要以CeO₂物相存在.     

Plasma chemical preparation and characterization of perovskite-type mixed oxides

The microwave plasma enhanced chemical vapour deposition (MPECVD) was applied for the preparation of perovskite-like mixed oxides, using either the metal acetylacetonates or metal nitrates as precursors. The same materials were prepared by the citrate method as reference substances. The obtained mixed oxides were calcined at 1100 °C, tested in the methane oxidation up to 1000 °C and characterized by X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), inductive coupled plasma–optical emissions spectroscopy (ICP–OES) and specific surface area (BET) determination. These studies revealed that LaMnO₃ with La³⁺ cation partly substituted by Sr, Ce and Ba cations and La_0.9Sr_0.1Co_0.9Fe_0.1O₃ calcined at 1100 °C seem to be highly active and stable catalysts in methane oxidation. In the case of LaMnO₃ and La_0.9Ce_0.1MnO₃ lowest light-off temperatures were reached with the catalysts prepared by the plasma method.     

镁基复合氧化物催化烯烃环氧化反应

 制备了一系列镁基复合氧化物 MgM-n 样品 (M = Sn, Al, Ti, La, Ce, Zr; n 为 Mg/M 原子比), 用 X 射线衍射、N2 吸附-脱附、CO2 程序升温脱附、紫外可见漫反射光谱和电子自旋共振等手段表征了它们的结构和表面性质, 并考察了其以过氧化氢为氧化剂催化烯烃环氧化反应性能. 结果表明, MgM-n 样品表面碱量和催化性能与其中 M 的种类及含量密切相关. MgSn-4 样品的表面碱量比 MgAl-4 低, 虽两者在催化苯乙烯环氧化反应中, 苯乙烯转化率和环氧化物选择性均为 95% 左右, 过氧化氢利用率大于 80%, 但在循环使用过程中 MgSn-4 的催化性能更为稳定, 并在不同结构烯烃的环氧化反应中表现出优良的催化性能. 这除与 MgSn-4 表面碱强度适当有关外, 还与其中存在高分散的 Sn4+物种及其结构特性有关.     

A Rapid Microwave-Induced Solution Combustion Synthesis of Ceria-Based Mixed Oxides for Catalytic Applications

We have been exploring the utilization of a simple and fast microwave-induced solution combustion synthesis technique for the preparation of various ceria-based mixed oxides for different catalytic applications. In our comprehensive investigation, CeO₂–SiO₂ (MWCS), CeO₂–TiO₂ (MWCT), CeO₂–ZrO₂ (MWCZ) and CeO₂–Al₂O₃ (MWCA) mixed oxides were synthesized by solution combustion synthesis method using microwave dielectric heating and employed for CO and soot oxidation applications. The intricate relationship between ceria and other supporting oxides has been explored with the help of various analytical techniques namely, X-ray diffraction (XRD), temperature programmed reduction/oxidation (TPR/TPO), temperature programmed desorption (TPD) of ammonia and CO₂, Raman spectroscopy (RS), UV–vis diffuse reflectance spectroscopy (UV–vis DRS), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), BET surface area and thermogravimetry analysis (TGA) methods. XRD results revealed amorphous nature of the material in case of ceria-silica mixed oxide and formation of a specific cubic fluorite type Ce_0.5Zr_0.5O₂ solid solution in the case of ceria-zirconia mixed oxide. Ceria-titania and ceria-alumina mixed oxides exhibited diffraction lines only due to crystalline ceria. Zirconia-based mixed oxide exhibited a lower reduction temperature and better redox properties compared to other samples. TPD of ammonia and CO₂ results revealed superior acid–base properties for MWCS mixed oxide. TGA measurements indicated a complete combustion in all preparations. RS results suggested defective structure of mixed oxides resulting in the formation of oxygen vacancies. XPS results revealed that ceria-zirconia mixed oxide contained more Ce³⁺ compared to other oxides. Among all the mixed oxides, the MWCZ sample exhibited a higher oxygen storage capacity, and better CO and soot oxidation activities. All these interesting findings have been elaborated in this publication.     

Electrooxidation of nitrite on a silica-cerium mixed oxide carbon paste electrode

A silica-cerium mixed oxide (SiCe) was prepared by the sol-gel process, using tetraethylorthosilicate and cerium nitrate as precursors and obtained as an amorphous solid possessing a specific surface area of 459 m(2) g(-1). Infrared spectroscopy of the SiCe material showed the formation of the Si-O-Ce linkage in the mixed oxide. Scanning electron microscopy/energy dispersive spectroscopy indicated that the cerium oxide particles were homogenously dispersed on the matrix surface. X-ray diffraction and (29)Si solid-state nuclear magnetic resonance implied non-crystalline silica matrices with chemical environments that are typical for silica-based mixed oxides. X-ray photoelectron spectroscopy showed that Ce was present in approximately equal amounts of both the 3+ and 4+ oxidation states. Cyclic voltammetry data of electrode prepared from the silica-cerium mixed oxide showed a peak for oxidation of Ce(3+)/Ce(4+) at 0.76 V and electrochemical impedance spectroscopy equivalent circuit indicated a porous structure with low charge transfer resistance. In the presence of nitrite, the SiCe electrode shows an anodic oxidation peak at 0.76 V with a linear response as the concentration of the analyte increases from 3×10(-5) at 3.9×10(-3) mol L(-1).     

Photocatalytic Activity of Fibrous Ti/Ce Oxides Obtained by Hydrothermal Impregnation of Short Flax Fibers

Fibrous Ti/Ce oxide photocatalysts were prepared for the first time by a biomimetic solution process using short flax fibers (flax straw processing waste) as a biotemplate. Titanium polyhydroxy complex solutions with 3% and 5% cerium were used as precursors. Flax fibers were impregnated in an autoclave under hydrothermal conditions. Ti/Ce oxides were obtained from the biotemplate by annealing at 600 °C. The photocatalytic activity of the Ti/Ce oxides was studied by the adsorption and decomposition of the dye rhodamine B under UV irradiation. The photocatalytic decomposition of the dye was 50% and 75% faster for Ti/Ce oxides with 3% and 5% Ce, respectively, than for the analogous undoped fibrous TiO₂. The morphologies, textures, and structures of the photocatalysts were studied by scanning electron microscopy, low temperature N₂ adsorption/desorption, UV-Vis spectroscopy, and X-ray and XPS analytical methods. It was shown that the introduction of Ce into the precursor solution increased the surface irregularity of the Ti/Ce oxide crystallites compared to pure TiO₂. This effect scaled with the Ce concentration. Ce improved the UV light absorption of the material. The Ti/Ce oxides contained Ce⁴⁺/Ce³⁺ pairs that played an important role in redox processes and intensified the photocatalytic activity.     

Copper-containing polymethylsilsesquioxane nanocomposites in catalytic olefination reaction

New copper-containing organosilicon hybrid materials were synthesized by the reaction of branched polymethyl- silsesquioxane with copper nanoparticles prepared by the metal-vapor synthesis. Hybrid materials showed a high activity in the catalytic olefination of p-chlorobenzaldehyde hydrazone with polyhaloalkanes such as CBrCl₃, CBr₄ and CF CBr to afford the corresponding halostyrenes in the yields above 80%. The structure and composition of the prepared nanocomposites were studied by X-ray using synchrotron radiation to show that the active sites of the catalysts are mixed copper(I)–copper(II) oxides (Cu–Cu₂O–CuO) in nature.     

Cu取代对水滑石前驱物及其衍生氧化物性能的影响

The coprecipitation method was used to prepare a series of different oxides (CuO: 0, 5%, 10%, 15%, 20%, 30% and 40%) derived from Cu substituted Mg/Al mixed anionic clay precursors (hydrotalcites) at the ratio of M2+/M3+ =3. In order to study influences of Cu and Mg content upon the performance of these materials, such characterization techniques as X-ray diffraction, thermogravimetrical analysis, differential scanning calorimetry, temperature programmed reaction and Fourier transform infrared reflectance spectra, were used. The results showed that complete structure of hydrotalcite precursors could be formed when CuO≤30%. When CuO≥40%, Cu(OH)2 phase appeared. Homogeneous composite oxides can be obtained by high temperature calcination at CuO≤20%. When CuO>20%, CuO phase was isolated. The content of Cu and Mg had significant influences on thermal stability of materials. The reduction ability of materials was related to calcination temperatures and material composition.     

MCM-41负载的La,Ce和Pt催化剂上三氯乙烯的低温催化燃烧

 分别采用直接水热合成法和浸渍法制备了Si-MCM-41, La-Si-MCM-41和Ce-Si-MCM-41介孔材料及其负载的Pt催化剂. 小角X射线衍射、氮气吸附和扩展X射线精细结构分析表明, La和Ce元素进入了MCM-41分子筛的骨架结构. NH3程序升温脱附测试未检测到含La和Ce样品表面的酸性. 所制备的催化剂具有较高的三氯乙烯催化燃烧活性及生成CO2和HCl的选择性.     

纳米 Ce1MgxZr1-xO2 固体多相催化剂的制备、表征及催化合成四氢苯并[b]吡喃衍生物的性能

 A series of Ce1MgxZr1-xO2 mixed metal oxides with different molar ratios were prepared by simple co-precipitation and were characterized by X-ray diffraction, infrared spectroscopy, scanning electron microscopy, energy dispersive spectroscopy, temperature-pro- grammed desorption of CO2, and N2 adsorption techniques. The prepared materials were tested for catalytic activity by the synthesis of tet-rahydrobenzo[b]pyran derivatives using a three component reaction (aromatic aldehydes, malononitrile, and dimedone) in an ethanol me-dium. The best catalytic activity was obtained with Ce1Mg0.6Zr0.4O2. The particle size or crystallite size was estimated using the De-bye-Scherrer equation. The addition of magnesium oxide into the ceria-zirconia lattice resulted in the formation of nanosized particles rang-ing from 5.41 to 9.78 nm. This work describes the catalytic behavior of magnesium oxide in mixed metal oxide systems.     

ZnO–Al2O3–CeO2–Ce2O3 mixed metal oxides as a promising photocatalyst for methyl orange photocatalytic degradation

In this research article, ZnO–Al₂O₃–CeO₂–Ce₂O₃ mixed metal oxides phases were prepared by calcination of Zn–Al/Ce–CO₃ layered double hydroxides (LDH) precursors, and evaluated for the photocatalytic degradation of methyl orange (MO) as a model textile dye from aqueous solution under UV irradiation. First, Zn–Al–CO₃ and a series of Zn–Al/Ce–CO₃ with different Ce content (5, 10, 15, 20%) were synthesized through co-precipitation method at Zn/(Al+Ce) molar ratio (r) of 3, then subjected to calcination at 500 °C for 6 h. Samples were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy coupled with energy dispersive X-ray analysis and pH point of zero charge. The experimental results of the photodegradation reveal that the photocatalyst developed from Zn–Al–Ce10%-CO₃ LDH exhibits the highest photocatalytic activity, with a degradation efficiency of 99.8% after 300 min of irradiation. This performance was mainly ascribed to the presence of difference state of Ce, leading a highest separation efficiency of electrons and holes. The recycling tests suggests a much high photostability and reusability of the photocatalyst.     

How temperature influences the stoichiometry of CeTi2O6

Of the many materials examined for the sequestration of nuclear waste, Ti oxides have received considerable attention. Brannerite (UTi₂O₆), in particular, has been studied extensively for this application. The Ce analogue of this material (CeTi₂O₆) has been widely investigated instead of the actinide versions owing to the reduced safety hazards and because Ce has similar crystal chemistry to U and Pu. In this study, examination of Ti K-, Ce L₃-, and Ce M_4,5-edge XANES spectra lead to the conclusion that CeTi₂O₆ was O-deficient when synthesized at high temperature and then quench cooled, and that the degree of O-deficiency was reduced upon post-annealing at lower temperatures. These observations can be ascribed to a temperature-dependant Ce³⁺/Ce⁴⁺ redox couple. This investigation suggests that Ce-containing materials may not properly simulate the actinide-bearing analogues; however, CeTi₂O₆ could be useful for other applications, such as catalysis.     

Catalytic properties of Ce<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Zr<Subscript>1–<Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>2</Subscript> prepared using a template in the oxidation of CO

The catalytic activity in CO oxidation of Ce _x Zr_1–x O₂ double oxides prepared using pine sawdust and cetyltrimethylammonium bromide (CTAB) as templates is compared. It is found by means of SEM and the low-temperature adsorption of N₂ that biomorphic oxides reproduce the macropore structure of the template. It is shown via XRD and Raman spectroscopy that all samples contained mixed ceria-zirconia oxide. The double oxides form a cubic phase with a lattice of the fluorite type at a ratio of Ce: Zr = 4, regardless of the nature of the template; when Ce: Zr = 1, the biomorphic mixed oxide forms a tetragonal phase. According to Raman spectroscopy and XRD it was shown that the distortion of the oxygen sublattice is higher in biomorphic samples. Energy dispersive analysis shows that Ca impurities were present in the biomorphic samples, introducing additional distortions in the lattice of double oxide and leading to the formation of anionic vacancies. It is found that when Ce: Zr = 4, the conversion of CO on biomorphic oxide in the range of 100–350°C is higher than that observed for Ce _x Zr_1–x O₂ (CTAB); reducing the Ce: Zr ratio in the biomorphic sample to 1 results in a marked decrease in CO conversion at 100–200°C. It is concluded that these differences are due to changes in the mobility of the lattice oxygen.     

Promotional effect of Ce on the SCR of NO with NH<Subscript>3</Subscript> at low temperature over MnO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> supported by nitric acid-modified activated carbon

Different amounts of Mn and Ce oxides were loaded onto nitric acid-modified activated carbon (ACN) by wet impregnation. The series of catalysts were employed for the selective catalytic reduction of NO _x by NH₃ at temperatures between 100 and 250 °C. Cerium-modified catalysts exhibited higher de-NO _x performance than those modified with Mn/ACN, even with the same total loadings. The precursor solution with a molar ratio for Ce/(Mn + Ce) of 0.4 exhibited the highest catalytic activity. Enhanced resistance to SO₂ and H₂O and better stability were observed for 10%Mn–Ce(0.4)/ACN relative to 10%Mn/ACN. The catalysts were further characterized by N₂ physisorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), hydrogen temperature-programmed reduction (H₂-TPR), and temperature-programmed desorption of ammonia (NH₃-TPD). The N₂ physisorption and XRD results suggested that co-doping Ce with Mn increased the surface area and promoted the dispersion of Mn–Ce binary metal oxides. H₂-TPR the NH₃-TPD results demonstrated that the interaction between manganese oxide and cerium oxide species enhanced the redox and surface acidity of 10%Mn–Ce(0.4)/ACN.     

纳米La0.8A’0.2Mn1-xCuxO3（A’=Ce and/or Sr）的制备、表征及其高效催化NO+CO的性能研究

采用柠檬酸-溶胶凝胶法制得钙钛矿型复合氧化物La0.8Ce0.2Mn1-xCuxO3(x=0.2,0.3,0.4),La0.8Sr0.2Mn0.6Cu0.4O3,La0.8Ce0.1Sr0.1Mn0.6 Cu0.4 O3,并采用X射线衍射(XRD)、扫描电镜(SEM)、比表面积(BET)、X射线光电子能谱(XPS)对其进行表征,测试了复合氧化物对CO+NO的催化活性。结果表明:La0.8Ce0.1Sr0.1Mn0.6Cu0.4O3催化活性最好,150℃时CO转化率91.8%,300℃时NO转化率100%;对于La0.8Ce0.2Mn1-xCuxO3(x=0.2,0.3,0.4),比表面积和颗粒的大小及分散度是影响催化活性的主要因素;对于La0.8Ce0.2Mn0.6Cu0.4O3,La0.8 Sr0.2 Mn0.6 Cu0.4 O3,La0.8 Ce0.1 Sr0.1 Mn0.6 Cu0.4 O3,催化剂的组成是影响催化活性的关键因素。