CeO2-Co3O4 Catalysts for CO Oxidation

CeO2-Co3O4 catalysts for low-temperature CO oxidation were prepared by a co-precipitation method. In combination with the characterization methods of N2 adsorption/desorption, XRD, temperature-programmed reduction （TPR）, and FT-IR, the influence of the cerium content on the catalytic performance of CeO2-Co3O4 was investigated. The results indicate that the prepared CeO2-Co3O4 catalysts exhibit a better activity than that of pure CeO2 or pure Co3O4. The catalyst with the Ce/Co atomic ratio 1 ： 16 exhibits the best activity, which converts 77% of CO at room temperature and completely oxidizes CO at 45 ℃.     

La-Ce-Cu复合金属氧化物的结构表征及催化性能

本文用ＮＨ４ＮＯ３共熔法合成Ｌａ－Ｃｅ－Ｃｕ系列样品。用ＸＲＤ分析了ＣｅＯ２在铜酸镧盐中的溶解度,发现大量ＣｅＯ２存在时,Ｌａ２Ｏ３、ＣｕＯ的加入导致原晶体结构发生变形,生成少量铜酸镧盐。ＸＲＦ分析了系列样品组成均为氧缺陷型化合物。ＸＰＳ研究发现,含大量ＣｅＯ２的样品高温焙烧后在ＣｅＯ２表面生成复合金属氧化物Ｌａ２ＣｕＯ４,最表面一层为少量Ｌａ２Ｏ３,并确定了其中Ｏ的属性。利用ＴＥＭ研究了部分样品的表面结构,同时研究了其ＣＯ催化氧化活性。     

Infrared spectroscopy analyses of air-CH4 or air-CO gas flows interacting with polycrystalline CeO2, La2O3 and Lu2O3 oxides

A comparative study of reactivity between air-CH4 or air-CO gas flows and CeO2, La2O3 and Lu2O3 rare earth oxides was performed using Fourier transform infrared spectroscopy analyses of CO2 gas resulted from the conversion of CH4 or CO gases. Polycrystalline samples of CeO2, La2O3 and Lu2O3 were first prepared by specific precipitation methods followed by low temperature calcination process. In the case of Lu2O3 oxide, a new specific route was proposed. Crystallite dimensions were determined by X-ray diffraction and transmission electron microscopy analyses. Morphologies were characterized using scanning electron microscopy. Specific surface areas were determined from Brunauer-Emmett-Teller (BET) technique. Using infrared spectroscopy analyses, the conversion rates of CH4 or CO into CO2 were determined from the evolutions of CO2 vibrational band intensities, as a function of time and temperature. It was clearly established that, despite its low specific surface, the Lu2O3 oxide presented the highest capacity of conversion of CH4 or CO into CO2.     

Synthesis of mesoporous CeO2-MnOx binary oxides and their catalytic performances for CO oxidation

Mesoporous CeO2-MnOx binary oxides with different Mn/Ce molar ratios were prepared by hydrothermal synthesis and characterized by scanning electron microscopy （SEM）, N2 sorption, X-ray diffraction （XRD）, X-ray photoelectron spectroscopy （XPS） and H2 temperature-programmed reduction （H2-TPR）. The characterization results indicated that the CeO2-MnOx catalysts exhibited flower-like microspheres with high specific surface areas, and partial Mn cations could be incorporated into CeO2 lattice to form solid solution. The CeO2-MnOx catalysts showed better catalytic activity for CO oxidation than that prepared by the coprecipitation method. Furthermore, the CeO2-MnOx catalyst with Mn/Ce molar ratio of 1 in the synthesis gel （Ce-Mn-1） exhibited the best catalytic activity, over which the conversion of CO could achieve 90% at 135 ℃. This was ascribed to presence of more Mn species with higher oxida- tion state on the surface and the better reducibility over the Ce-Mn-I catalyst than other CeO2-MnOx catalysts.     

Preparation and characterization of Ce1-xFexO2 complex oxides and its catalytic activity for methane selective oxidation

A series of Ce1-xFexO2 （x=0, 0.2, 0.4, 0.6, 0.8, 1） complex oxide catalysts were prepared using the coprecipitation method. The catalysts were characterized by means of XRD and H2-TPR. The reactions between methane and lattice oxygen from the complex oxides were investigated. The characteristic results revealed that the combination of Ce and Fe oxide in the catalysts could lower the temperature necessary to reduce the cerium oxide. The catalytic activity for selective CH4 oxidation was strongly influenced by dropped Fe species. Adding the appropriate amount of Fe2O3 to CeO2 could promote the action between CH4 and CeO2. Dispersed Fe2O3 first returned to the original state and would then virtually form the Fe species on the catalyst, which could be considered as the active site for selective CH4 oxidation. The appearance of carbon formation was significant and the oxidation of carbon appeared to be the rate-determining step; the amounts of surface reducible oxygen species in CeO2 were also relevant to the activity. Among all the catalysts, Ce0.6Fe0.402 exhibited the best activity, which converted 94.52% of CH4 at 900 ℃.     

不同沉淀剂制备氧化铈抛光粉

氧化铈(CeO₂)抛光粉在光学玻璃、手机盖板、集成电路等领域内有着广泛的应用。合成高端CeO₂抛光粉主要采用液相沉淀得到前驱体,再经过煅烧转型制得CeO₂。前驱体是决定CeO₂抛光粉性质和性能的关键因素之一。通过模拟工业上常用的制备方法,以氯化铈(CeCl₃)为铈源,使用碳酸钠(Na₂CO₃)、碳酸铵[(NH₄)₂CO₃]、碳酸氢铵(NH₄HCO₃)、二水合草酸(H₂C2O₄·2H₂O)和氢氧化钠(NaOH)为沉淀剂,合成了一系列CeO₂抛光粉的前驱体。利用X-射线衍射仪(XRD)、扫描电子显微镜(SEM)、激光粒度仪等手段表征了前驱体的晶相、形貌、粒度等性质,并研究了前驱体煅烧转型后的CeO₂性质及其对K9光学玻璃的...     

Preparation and characterization of Ce-Fe-Zr-O(x)/MgO complex oxides for selective oxidation of methane to synthesize gas

A series of Ce-Fe-Zr-O(x)/MgO(x denotes the mass fraction of Ce-Fe-Zr-O,x=10%,15%,20%,25%,30%) complex oxide oxygen carriers for selective oxidation of methane to synthesis gas were prepared by the co-precipitation method.The catalysts were characterized by means of X-ray diffraction and H2-TPR.The XRD measurements showed that MgFeO4 particles were formed and Fe2O3 particles well dispersed on the oxygen carriers.The reactions between methane diluted by argon(10% CH4) and oxygen carriers were investigated.Suitable content of CeO2/Fe2O3/ZrO2 mixed oxides could promote the reaction between methane and oxygen carriers.There are mainly two kinds of oxygen of carriers:surface lattice oxygen which had higher activity but lower selectivity,and bulk lattice oxygen which had lower activity but higher selectivity.Among all the catalysts,Ce-Fe-Zr-O(20%)/MgO exhibited the best catalytic performance.The conversion of the methane was above 56%,and the selectivity of the H2 and CO were both above 93%,the ratio of H2/CO was stable and approached to 2 for a long time.     

CuO／CeO2 Catalysts for Selective Oxidation of Carbon Monoxide in Excess Hydrogen

CuO/CeO2 catalysts were prepared by a coprecipitation method and tested for CO removal from reformed fuels via selective oxidation. The influence of the calcination temperature on the chemical compositions and catalytic performance of CuO/CeO2 catalysts were studied. It was found that CuO/CeO2 catalysts exhibit excellent CO oxidation activity and selectivity, and the complete removal of CO is attained when the catalysts are calcined at appropriate temperatures. XRD, TPR and XPS results indicate that CuO/CeO2 catalysts exhibit higher catalytic performance in CO selective oxidation due to the strong interaction between copper oxide and cerium dioxide, which promotes the dispersion and hydrogen reduction activity of copper.     

Catalytic Partial Oxidation of Methane over Ni/CeO2-ZrO2-Al2O3

Nickel catalysts supported on CeO2-ZrO2-CeO2,ZrO2-Al2O3 and Al2O3 were prepared and characterized by means of X-ray diffraction（XRD）,BET areas,H2 temperature-programmed reduction（H2-TPR）,and X-ray photoelectron spectroscopy（XPS）.Through the test of catalytic partial oxidation of methane（CPOM）,Ni/CeO2-ZrO2-Al2O3 displayed the highest activity,which resulted from its largest BET area and best NiO dispersion.Furthermore,Ni/CeO2-ZrO2-Al2O3 maintained a long-time stability in CPOM,which was attributed to its best coking resistance among all the prepared catalysts.     

Effects of CeO2 on structure and properties of Ni-Mn-K/bauxite catalysts for water-gas shift reaction

Multiple-metal catalysts (Ni-Mn-Ce-K/bauxite) for Water-Gas Shift (WGS) reaction were prepared by impregnation, and the catalytic structure and properties were investigated by N2 physical, XRD, H2-TPR, and CO-TPD. The results indicated that the addition of 7.5% CeO2 improved the activity of the WGS reaction obviously, and also increased the specific surface area and pore volume of the catalysts. The addition of CeO2 decreases the reduction temperature, enhanced the adsorption and activation of H2O, and improved the adsorption content of CO. Besides, active sites were not changed and the number of active sites on catalysts did not increase obviously.     

Preparation, Characterization of CuO／CeO2 and Cu／CeO2 Catalysts and Their Applications in Low-Temperature CO Oxidation

CeO2 was synthesized via sol-gel process and used as supporter to prepare CuO/CeO2, Cu/CeO2 catalysts by impregnation method. The catalytic properties and characterization of CeO2, CuO/CeO2 and Cu/CeO2 catalysts were examined by means of a microreactor-GC system, HRTEM, XRD, TPR and XPS techniques. The results show that CuO has not catalytic activity and the activity of CeO2 is quite low for CO oxidation. However, the catalytic activity of CuO/CeO2 and Cu/CeO2 catalysts increases significantly. Furthermore, the activity of CuO/CeO2 is higher than that of Cu/CeO2 catalysts.     

Catalytic combustion study of soot on Ce0.7Zr0.3O2 solid solution

The Ce0.7Zr0.3O2 solid solution and CeO2 were prepared using the sol-gel method. The phase structure, crystallite sizes and the reducibility of the catalysts were characterized by XRD and H2-TPR techniques. XRD results indicated that Zr^4＋ had replaced part of Ce^4＋ to form a fluorite-like solid solution, which was favorable to obtain ultrafine nanoparticles. The ratio of main HE consumption for Ce0.7Zr0.3O2：CeO2 was 4.4：1.0, implying that the solid solution could improve the reducibility compared to the single CeO2. The Ce0.7Zr0.3O2 solid solution catalyst showed a sharp combustion peak at 397 ℃, which was 200 ℃ lower than that of the single soot. The good catalytic activity of the Ce0.7Zr0.3O2 was attributed to the formation of nano-CeO2-based solid solution, which enhanced the reducibility and then improved the combustion activity. As Ce0.7Zr0.3O2 could be easily reduced to Ce0.7Zr0.3O2-x meanwhile, after oxygenation, the Ce0.7Zr0.3O2.x was recovered to Ce0.7Zr0.3O2 completely. A catalytic combustion reaction mechanism was proposed： the Ce0.7Zr0.3O2 was reduced to Ce0.7Zr0.3O2-x by the reaction with carbon and then it was recovered to Ce0.7Zr0.3O2-x by the interaction with O2.     

Structures and oxygen storage capacities of CeO2-ZrO2-Al2O3 ternary oxides prepared by a green route： supercritical anti-solvent precipitation

CeO2-ZrO2-Al2O3 ternary oxides were successfully prepared by a green route of supercritical anti-solvent precipitation with supercritical CO2 as anti-solvent and methanol as solvent.The structures and oxygen storage capacities of these ternary oxides were characterized by XRD,Raman spectra and oxygen storage capacity measurements.It was found that Al 3+ and Zr 4+ inserted into CeO2 lattice,forming CeO2-ZrO2-Al2O3 solid solution.The concentration of aluminium isopropoxide in the solution affected the concentration of oxygen vacancy and the distortion of oxygen sublattice which were responsible for the oxygen storage capacity.The rapidest oxygen uptake/release rate and maximum total oxygen storage capacity(122.0 mmolO2/molCeO2)were obtained with the aluminium isopropoxide concentration at 0.2 wt.% in the solution.     

Valence State of Active Copper in CuOx/CeO2 Catalysts for CO Oxidation

CuOx/CeO2 catalysts were prepared by adsorption-impregnation method, CO conversion was tested over the catalysts pretreated under different conditions for preferential CO oxidation in H2, and the catalysts were characterized with X-ray photoelectron spectroscopy and temperature programmed reduction. Experimental results show that there are two kinds of copper, which are Cu^＋ and Cu^2＋ in calcined CuOx/CeO2, Among them, the Cu^＋ is the key active component for CO oxidation. The main reason is as follows： CO is activated by copper for CO oxidation over CuOx/CeO2, while CO can not be activated by Cu^2＋. Only when Cu^2＋ is reduced to Cu ^＋ or Cu^0, the copper may be active for CO oxidation, moreover, the experimental results show that the reduction of Cu^2＋ does not lead to an increase of catalytic activity. So the active species is Cu^＋ in CuOx/CeO2 catalysts.     

Preferential Oxidation of Carbon Monoxide in Excess Hydrogen over Au/Co3O4-CeO2 Catalysts

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Preparation and CO conversion activity of ceria nanotubes by carbon nanotubes templating method

Ceria nanotubes with high CO conversion activity by means of carbon nanotubes as removable templates in the simple liquid phase process were fabricated under moderate conditions. The pristine CNTs were first pretreated by refluxing in a 30% nitric acid solution at 140 ℃ for 24 h, then dispersed in an ethanolic Ce（NO3）3.6H2O solution with ultrasonic radiation at room temperature for 1 h. Under vigorous stirring, NaOH solution was added drop by drop into the above ethanolic solution until the pH value was 10. The product was collected and repeatedly washed with ethanol and on drying at 60 ℃, the CeO2/CNT composites were obtained. Then, the as-prepared composites were heated at 450 ℃ in an air atmosphere for 30 min to remove CNTs. The ceria nanotubes were characterized by X-Ray Diffraction （XRD）, Transmission Electron Microscopy （TEM）, and X-Ray Photoelectron Spectrum （XPS）. The results showed that the ceria nanotubes were polycrystalline face-centered cubic phase and were composed of lots of dense cefia nanoparficles. The diameter of cefia nanotubes was about 40-50 nm. Catalytic activity of the product for CO oxidation was carded out at the region of 30-300 ℃ in a U-shaped quartz reactor with feeding about 0.15 g of the catalyst, which was loaded on Al2O3 carder. The inlet gas composition was 1.0% CO and 28% O2 with N2 as balance, and the rate of flow was kept at 40 ml/min. The catalytic products were analyzed by gas chromatography. The as-repared CeO2 nanotubes showed higher CO oxidation activity, which indicated that the morphology of ceria products affected the catalytic performance. The ceria nanotubes supported on Al2O3 demonstrated that conversion temperature for CO oxidation to CO2 was lower than that for bulk catalysts.     

Catalytic Reduction of SO2 on CeO2-La2O3 Rare Earth Mixed Compounds

Adding rare earth oxide CeO2 with variable valences to La2O3 formed a mixture of rare earth oxides. By means of dipping CeO2, La2O3 and their mixture, whose carriers were all γ-Al2O3, were used as the catalyst for the reduction of SO2 by CO. The activation process of this catalyst and the impact of temperature and reactant concentration on the activation process were investigated. Using X-ray diffraction, the structure characteristics of catalyst before and after reaction were analyzed to reveal the change of phase structure. The result shows that the rare earth oxide mixtures composing of CeO2 and La2O3, as the catalyst for the reduction of SO2 by CO, diminish activation temperature 50～100℃ less and have higher activity than a single oxide CeO2 or La2O3. The reason possibl is that La2O3 goes into in the lattice of CeO2 to form solid phase complex CeO2-La2O3 and increases the capability of CeO2-La2O3/γ-Al2O3 catalyst to store oxygen, which supplies the redox of CeO2 reaction with a better condition. At the same time, elemental sulfur formed in the redox reaction impels La203 to be transformed to activation phase La2O2S in a lower temperature, which can be explained with the synergism between redox reaction and COS intermediate mechanism reaction.     

Influence of Additives Ceria and Lanthana on Performance of Pd／Al／Monolith Honeycomb Catalysts

The effects of ceria and lanthana additives on activity and thermal stabilization of the catalysts for CO oxidation were studied. The results show that the addition of CeO2 clearly improves the catalytic activity, which may derive from the synergic effect between CeO2 and PdO. The catalysts were characterized by means of temperature-programmed reduction (TPR) and X-ray photoelectron spectroscopy (XPS) measurements. The XPS results of a slight increase in metal oxidation state reflect that the charge transfers from metal to ceria and ceria is slightly reduced, which leads to a decrease of the Ce-O bond strength. Pd-Ce synergism affects the reduction behavior of the catalysts. The TPR results show that the CeO2 ad-dition lowers the reduction temperature of PdO, while palladium facilitates the reduction of the ceria. For PdO/La2O3/Al2O3/monolith honeycomb catalysts, the aging test measurements at 1050 ℃ and the XRD results show that the formation of LaAlO3 which neutralizes the surface alumina defects inhibits the sintering of alumina.     

Influence of Supports on Catalytic Performance and Carbon Deposition of Palladium Catalyst for Methane Partial Oxidation

The catalytic performance of methane partial oxidation was investigated on Pd/CeO2-ZrO2 and Pd/α-Al2O3 catalysts.The catalysts were characterized by XRD,Raman spectra,and TG-DTA techniques.The results show that CeO2-ZrO2 support is more advantageous for the catalytic activity and stability of catalysts compared to α-Al2O3.TG-DTA and Raman spectra results indicated that carbon deposited on the catalysts was in the form of graphite,which is the main reason for the deactivation of catalysts after a 24-hour reaction.Moreover,CeO2-ZrO2 had positive effect on inhibiting carbon deposition.     

Preparation and Characterization of Nanocrystalline CeO2 by Precipitation Method

CeO2 nanocrystalline particulates with different sizes were prepared by precipitation method using ethanol as dispersive and protective reagent. XRD spectra show that the synthesized CeO2 has cubic crystalline structure of space group OH^H-FM3M, when calcination temperature is in the range of 250 - 800 ℃. TEM images reveal that CeO2 particles are spherical in shape. The average size of the particles increases with the increase of calcination temperature. Thermogravimetric analysis indicates that the weight loss of precursor mainly depends on the calcination temperature, and little depends on the calcination time. Measurements of CeO2 relative density show that the relative density of CeO2 nanocrystalline powders increases with increasing CeO2 particle size.