Temperature Programmed Reduction Studies on CeO2-Containing Catalysts

Temperature programmed reduction (TPR) study was carried out for CeO2/A12O3 and CeO2/ZrO2 catalysts to evaluate oxygen storage property induced by a facile redox cycling of Ce ion. The CeO2/ZrO2 catalyst possesses excellent oxygen storage activity at 373 K after reduction above 1173 K although the oxygen storage of CeO2/Al2O3 catalyst after reduction above 1173 K is poor because of the formation of CeAlO3. Consequently, the oxygen storage on the CeO2/ZrO2 catalyst smoothly occurs from low temperatures when the catalyst is reduced even at high temperatures.     

Effect of doping rare earth oxide on performance of copper-manganese catalysts for water-gas shift reaction

Rare earth-doped copper-manganese mixed oxide catalysts were prepared by coprecipitation and mechanical mixing using copper sulfate, manganese sulfate, and rare-earth oxides REO （REO indicates La2O3, CeO2, Y2O3, or Pr6O11） as raw materials. The samples were characterized by X-ray diffraction （XRD）, temperature-programmed reduction （TPR）, temperature-programmed reduc-tion of oxidized surfaces （s-TPR）, and temperature-programmed desorption （TPD）. Catalytic activities were tested for a water-gas shift reaction. Doping rare earth oxides did not alter the crystal structure of the original copper-manganese mixed oxides but changed the interplanar spacing, adsorption performance and reaction performance. Doping with La2O3 enhanced the activity and stability of Cu-Mn mixed oxides because of high copper distribution and fine reduction. Doping with CeO2 and Y2O3 also decreased the reduc-tion temperatures of the samples to different degrees while improving the dispersion of Cu on the surface, thus, catalytic activity was better than that of undoped Cu-Mn sample. The Pr6O11-doped sample was difficult to reduce, the dispersion of surface coppers was lowered, resulting in poor activity.     

Effects of La_2O_3 contents on the Pd/Ce_（0.8）Zr_（0.2）O_2-La_2O_3 catalysts for methanol decomposition

The catalytic behaviors of Pd (1.4 wt.%) catalysts supported on CeO2-ZrO2 promoted with La2O3 were investigated for methanol decomposition. The measurements of inductively coupled plasma emission spectroscopy (ICP), N2 adsorption-desorption (BET), powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR) and oxygen storage capacity (OSC) were used to characterize the properties of catalysts. The catalysts' activities were tested in a fixed bed continuous ...     

金属钕及氧化钕中稀土杂质光谱测定

在色散０．２５ｍｍ／ｍｍ光栅光谱仪上，以控制气氛直流电弧粉末地测定了金属钕及氧化钕中氧化镧、氧化铈、氧化镨、氧化钐、氧化钆、氧化镝和氧化钇。采用正交设计实验，确定了测定条件。测定的下限对氧化铈、氧化镨为０．０５％，氧化镧、氧化钐、氧化钆、氧化镝和氧化钇为０．０３％，相对标准偏差为６％￣１８％。     

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.     

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.     

Effect of BaO on Catalytic Activity of Pt-Rh TWC

The effects of BaO doping on the three-way catalytic activity of Pt-Rh catalyst and on water-gas shift were investigated. The results show that the light-off temperatures of hydrocarbon and carbon monoxide and nitrogen oxides of the fresh catalysts slightly differ from those of the aged catalysts, and the catalysts containing CeO2-ZrO2-BaO have lower lightoff temperature and better catalytic activity than these containing BaO and CeO2-ZrO2 after hydrothermal aging for 5 h at 1000 ℃. The catalysts were characterized by means of the temperature-programmed reduction （TPR） in hydrogen and the temperature-programmed desorption （TPD） in oxygen. It is confirmed that the suggested route of CeO2-ZrO2-BaO by coprecipitation can improve the catalytic activity of catalysts.     

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 ℃.     

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.     

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.     

Partial oxidation of methane on Ni/CeO2-ZrO2/γ-Al2O3 prepared using different processes

The influences of CeO2-ZrO2 and γ-Al2O3 mixing methods on the catalytic activity and stability of partial oxidation of methane (POM) were investigated over Ni/Ce0.7Zr0.3O2-Al2O3 catalysts. The catalysts were characterized by XRD, TPR, H2-chemsorption, and TG-DTA. For fresh catalysts, the results showed that the salt precursor mixing catalyst (ATOM) presented better performance than the catalysts prepared by the precipitator mixing method (MOL) and the powder mechanically mixing method (MECH). The result of XRD suggested that the interaction between CeO2-ZrO2 and Al2O3 in ATOM sample was stronger than the others, which led to more lattice defects and thereby better initial activity. Moreover, the MECH sample had the best stability and the least coke deposition in 24 h stability tests. The results of TPR and H2-chemsorption indicated that the intimate contact of Ni-Al in MECH sample enhanced the ability of resisting coke deposition and metal sintering.     

稀土对等离子束表面冶金涂层抗裂性的影响

 采用直流放电压缩电弧等离子束表面冶金技术，在Q235钢表面制备了添加La2O3和CeO2的铁基冶金涂层。研究了冶金涂层开裂的主要形式、稀土氧化物对冶金涂层组织及抗裂性的影响，初步探讨了稀土氧化物改善界面显微结构、抑制冶金涂层开裂的机制。结果表明：稀土除可与氧、硫、硼等反应外，还可固溶于晶内、晶界或晶界附近；添加适量的稀土氧化物可有效改善冶金涂层的组织和性能，抑制等离子束表面冶金涂层中的裂纹和孔洞。     

Effect of Ceria on Structure and Thermostability of Copper-Iron-Oxide Catalyst

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Preparation and Characterization of Cex Th1-xO2 Solid Solutions Prepared by Sol-Gel Method

Ceriumoxidehasbeenwidelystudiedinrecent yearsbecauseofitsusefulnessindifferentareasof chemistry.Incatalyticfield,forexample,CeO2has beenusedasanimportantcomponentofautomotive three waycatalystsforreducingtheexhaust.The mainroleofceriainthree waycatalystsi…     

Structure and oxygen storage capacity of Pr-doped Ce_（0.26）Zr_（0.74）O_2 mixed oxides

Binary Ce-Zr(CZ),Pr-Zr(PZ) and ternary Ce-Zr-Pr(CZP) mixed oxides were prepared by an ammonia-aided co-precipitation method,and were aged in a steam/air flow at 1050 °C.X-ray diffraction(XRD),Raman spectra,X-photon spectra(XPS) and CO temperature programmed reduction(TPR) were carried out to characterize the micro-structure and reducibility of catalysts.The oxygen storage capacity(OSC) was evaluated with CO serving as probe gas.The results showed that a pseudo cubic structure was formed for the Zr-rich ceria-zirconia mixed oxides with Pr doping.The insertion of Pr prevented the phase segregation of the mixed oxides during the hydrothermal ageing.The Pr doped samples showed better redox performances in comparison with CZ,and the sample doped with 5 wt.% Pr showed the most remarkably promoted dynamic oxygen storage capacity.This phenomenon was closely related to both the reducibility and oxygen mobility of the mixed oxides.The introduction of praseodymium into ceria-zirconia could accelerate the oxygen migration by increasing the amount of oxygen vacancies,although it was difficult for Pr3+ ions themselves to participate in the oxygen exchange process.     

Dynamic Oxygen Storage Capacity Measurements on Ceria-Based Material

The constant increase in the number of environ-mental protection regulations worldwide has broughtabout significant restrictions onthe nature and quantityof exhaust gases originating from mobile sources suchas automobile emissions .These increasingly dema…     

Preparation and characterization of Ce_1-xNi_xO₂ as oxygen carrier for selective oxidation methane to syngas in absence of gaseous oxygen

A citric acid complex method was employed to prepare Ce/Ni mixed oxides with various Ce/Ni ratios useful for selective oxidation methane to syngas in the absence of gaseous oxygen,and the catalytic activity measurement was investigated in a fixed bed reactor at 800 oC.The prepared oxygen carriers were characterized by various characterization techniques such as TG-DSC,XRD and TPR.The results of TG-DSC indicated that the Ce1-xNixO2 precursor generated a stable phase after the heat-treatment at temperatures above 800 oC.The XRD characterization suggested that some Ce-Ni solid solution was formed when Ni2+ ions was incorporated into the lattice of CeO2,and it led to the generation of O-vacancy which could improve the oxygen mobility in the lattice of oxygen carriers.It was found that Ce0.8Ni0.2O2 gave the highest activity in the selective oxidation methane to syngas reaction,and the average methane conversion,CO and H2 selectivity reached to 82.31%,82.41% and 87.64%,respectively.The reason could be not only attributed to the fitting amount of NiO dispersed on the CeO2 surface and bulk but also to actual lattice oxygen amount increased in oxygen carrier.     

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.     

Effect of Manganese Doping on Oxygen Storage Capacity of Ceria-Zirconia Mixed Oxides

CeO2-ZrO2-MnOx mixed oxide series were prepared by sol-gel method. CO pulse and CO-O2 cycle measurements were carried out to examine the oxygen storage complete capacity （OSCC） and dynamic oxygen storage capacity （OSC） of the samples. The doping method brought about strong interactions between manganese oxide and ceria, both in the bulk and on the surface. Only a small part of Mn cations are incorporated into the ceria lattice to form solid solutions and the remaining are left on the surface as finely dispersed Mn3O4. The OSC behaviors of the materials are influenced by the doping amount of Mn and the solubility of Mn in the CeO2 lattice. The OSC is more easily affected by available contents of oxygen storage components when the measurement frequency is low. Comparatively, the concentration of lattice defects, which affects the mobility of bulk oxygen, is the determining factor under high frequency.     

Steam reforming of ethanol over Ni/Ce0.7Pr0.3O2 catalyst

NiO/Ce0.7Pr0.3O2 catalysts were prepared by co-precipitation method and used for steam reforming of ethanol to produce hydrogen. The influence of nickel content and the doping of Pr on the catalytic performance were investigated. The catalysts were characterized by using temperature programmed reduction (TPR), X-ray diffraction (XRD) and thermal analysis techniques. 15 wt.%NiO/Ce0.7Pr0.3O2 catalyst was highly active and selective for steam reforming of ethanol to produce hydrogen. With the doping of Pr, the anti-carbon deposition property of the catalyst and the anti-sintering stability of metal nickel were effectively improved. The improvement of the anti-carbon deposition is attributed to generation of oxygen vacancies resulted from the Pr doping; while the improvement of anti sintering is ascribed to the intensified interaction between the nickel species and the support which is owing to the Pr-doping resulted incorporation of some nickel ions into ceria lattice.