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.     

Influence of cobalt on performance of Cu-CeO_2 catalysts for preferential oxidation of CO

Copper and cobalt oxides supported on CeO_2 were investigated for preferential oxidation of carbon monoxide(CO-PROX) in the presence of excess hydrogen and CO_2.(Cuo)_(1-x)(Co_3 O_4)_(x/3)-(CeO_2)_(2.5)(x=0,0.25,0.50,0.75,0.85 and 1) catalysts were prepared by coprecipitation method.These mixed oxide catalysts were characterized by several physicochemical techniques,such as BET surface area(S_(BET)),X-ray diffraction(XRD),high resolution transmission electron microscopy(HRTEM),temperature programmed reduction(TPR) and X-ray photoelectron spectroscopy(XPS).XRD studies show the peaks related to CuO and Co_3 O_4 phases in copper and cobalt containing CeO_2 catalysts.The average particle size of the CeO_2 crystallites is in the range of 8-10 nm as evaluated from HRTEM studies.XPS studies demonstrate that Cu,Co and Ce in(cuO)_(1-x)(Co_3O_4)_(x/3)-(CeO_2)_(2.5) catalysts are presented in+2 and +1,+3 and +2 and +4 and +3 oxidation states,respectively.The catalyst with x=0.75 shows better activity and selectivity towards CO-PROX.Though the catalyst with only copper(CuO-CeO_2,x=0) shows good activity but reverse water gas shift(RWGS) reaction is noticed at high temperature.On the other hand,RWGS reaction is suppressed on the cobalt containing CuO-ceO_2 catalyst.Cobalt on CeO_2 with x=1 shows hardly any activity for PRoX reaction at low temperatures.No methanation activity is observed on CuO-CeO_2 or Co_3O_4-CeO_2 catalysts.In contrast,combination of copper and cobalt on CeO_2 shows methanation of CO where enhanced activity is observed with increasing in cobalt content.     

Effect of Ce doping into V_2O_5-WO_3/TiO_2 catalysts on the selective catalytic reduction of NO_x by NH_3

In this work, the effectiveness of V_2O_5-WO_3/TiO_2 catalysts modified with different CeO_2 contents by impregnation and co-precipitation methods on the selective catalytic reduction of NOxby NH3 have been studied comparatively by various experimental techniques. The results showed that the NO conversion of V_2O_5-WO_3/CeO_2-TiO_2 catalysts modified by co-precipitation method obviously increased with the Ce doping contents in the studied range below 20%(All Ce contents are in mass fractions), but the NO conversion of V_2O_5-WO_3/CeO_2/TiO_2 catalysts modified by impregnation methods was lower than V_2O_5-WO_3/CeO_2-TiO_2 catalysts especially beyond 2.5% Ce doping contents. The V_2O_5-WO_3/CeO_2-TiO_2 catalysts showed better SCR activity, wider reaction window, and higher sulfur and water resistance. The characterization results elucidated that the modified catalysts by co-precipitation method exhibited higher specific surface area, much better dispersity of Ce component, more Ce~(3+)species and more Br?nsted acid sites than that by impregnation. The vacancies caused by more Ce~(3+)species were favorable for more NO oxidation to NO_2, and the interaction between Ce species and WOxspecies generated more Br?nsted acid sites. It could be supposed that dispersed Ce Oxspecies and WOxspecies offered more second active centers respectively to adsorb oxygen and activate ammonia as co-catalysis to the primary active center of V ions, thus facilitated the better SCR activity of modified V_2O_5-WO_3/CeO_2-TiO_2 catalysts by coprecipitation methods. The co-precipitation methods with Ce component were more suitable for production of modified commercial V_2O_5-WO_3/TiO_2 catalysts.     

Modification of Cu/ZSM-5 catalyst with CeO_2 for selective catalytic reduction of NO_x with ammonia

Cu/ZSM-5 and CeO_2-modified Cu/ZSM-5 catalysts were prepared by a wetness impregnation method. The addition of CeO_2 was found to enhance the NO_x selective catalytic reduction(SCR) activity of the catalyst at low temperatures, but the high-temperature activity was weakened. The catalysts were characterized by X-ray diffraction(XRD), nitrogen physisorption, inductively coupled plasma optical emission spectrometry(ICP-OES), X-ray photoelectron spectroscopy(XPS), electron paramagnetic resonance(EPR), H_2 temperature-programmed reduction(TPR) and NH_3 temperature-programmed desorption(TPD). The results showed that more CuO clusters instead of isolated Cu~(2+) species were obtained on the modified catalyst. These active CuO clusters, as well as the Cu-Ce synergistic effect, improved the redox property of the catalyst and low-temperatures SCR activity via promoting the oxidation of NO to NO_2 and fast SCR reaction. The loss in high-temperatures activity was attributed to the enhanced competitive oxidation of NH_3 by O_2 and decreased surface acidity of the catalyst.     

Au-Pd/ZnO-CeO_2催化剂甲醇部分氧化制氢性能的研究

采用聚合物保护乙醇还原法制备了Au-Pd/ZnO-CeO_2催化剂,考察了CeO_2对Au-Pd/ZnO催化剂甲醇部分氧化制氢反应性能的影响,并运用BET、XRD、TPR、H_2-TPD和CH_3OH-TPD等手段对催化剂进行了表征.结果表明,CeO_2对Au-Pd/ZnO催化剂具有较好的改性效果,CeO_2的引入能提高Au-Pd/ZnO催化剂的活性和氢气的选择性,归结于CeO_2的加入增加了催化剂的比表面积、分散度和对反应物甲醇的吸附,同时减少了对生成物H_2脱附,这些均有利于甲醇部分氧化制氢反应.     

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.     

新型稀土固体超强酸催化剂的制备及乳酸丁酯的合成

制备了一系列稀土固体超强酸催化剂,以乙酸丁酯为探针反应,考察了催化剂最佳制备条件;以乳酸和丁醇为原料,以S2O82-/ZrO2-SiO2-Sm2O3(BR-3%-0.75-450)为催化剂合成乳酸丁酯,研究了对酯化反应的影响因素、催化剂稳定性。实验结果表明,该催化剂活性和稳定性均优于未改性的SO42-/ZrO2-SiO2。     

采用固氟氯化法从氟碳铈矿中提取稀土氯化动力学的研究进展

针对我国主要的稀土矿物氟碳铈稀土矿目前在分解回收中主要采用浓硫酸焙烧法产生氟化氢污染环境的问题,清华大学核能与新能源研究院从1998年以来开展了氧化镁固氟、氯化铵选择性氯化提取氟碳铈中稀土及其动力学的研究。选择我国典型的稀土矿物包头混合型稀土矿及山东氟碳铈稀土矿展开研究,确定了适宜的工艺条件、氯化选择性和氟的转化形态。稀土以氯化稀土形式被浸取,对于两种稀土矿物稀土浸出回收率均在85%以上。氯化铵氯化稀土的氯化动力学符合Bagdasarym提出的多相区域反应动力学模型,氯化反应的速率αRE遵从Erofeev方程。氯化铵氯化不同形态氧化稀土氯化反应表观活化能的大小顺序为:EaLa2O3+CeO2相似文献   

Doping Effects of Rare Earth on Dielectric Properties of Fine-Grained BaTiO_3-Based Ceramics

Recently ,manystudiesonfine grainedBaTiO3 basedceramicsdopedwithrareearthelementshavebeenperformedbecauseitisharmlesstotheenviron mentbothinproductionandinapplication .Thiskindofmaterialiscommonlyusedasmultilayerceramicca pacitors (MLCC)ofEIAX7Rspecification .Theeffectsofrareearthoxidesonthedielectricpropertiesandreliabilityhavebeendiscussedinsever alrecentpapers ,whichconcludedthatrareearthox idesplayanimportantroleintheX7Rdielectricsandareveryeffectivetoenhancethereliabilitiesofdielec t…     

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.     

Effect of cerium oxide prepared under different hydrothermal time on electrocatalytic performance of Pt-based anode catalysts

In this paper,CeO_2 with a pore size of 2-4 nm was synthesized by hydrothermal method.The CeO_2 modified graphene-supported Pt catalyst was prepared by the microwave-assisted ethylene glycol reduction chloroplatinic acid method,and the effect of the addition of CeO_2 prepared by different hydrothermal reaction time on the catalytic performance of Pt-based catalysts was investigated.The microstructures of CeO_2 and catalysts were characterized by X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS),specific surface area and pore size analyzer(BET),scanning electron microscopy(SEM) and electron spectroscopy(EDAX),transmission electron microscopy(TEM),and the catalysts electrochemical performance was tested by electrochemical workstation.The results show that the catalytic performance of the four catalysts with CeO_2 is better than that of the catalyst without CeO_2.Adding CeO_2 with a specific surface area of 120.15 m~2/g prepared by hydrothermal reaction time of 39 h to Pt/C synthesis catalyst,its electrocatalytic performance,stability and resistance to poisoning are the best.The electrochemical active surface area is 102.83 m~2/g,the peak current density of ethanol oxidation is 757.17 A/g and steady-state current density of 1100 s is 108.17 A/g which shows the lowest activation energy for ethanol oxidation reaction.When the cyclic voltammogram is scanned for 500 cycles,the oxidation peak current density retention rate is 87.74%.     

Characteristics on Cerium Promoted Iron Based Catalyst forDehydrogenation Ethylbenzene to Styrene

ＣｈａｒａｃｔｅｒｉｓｔｉｃｓｏｎＣｅｒｉｕｍＰｒｏｍｏｔｅｄＩｒｏｎＢａｓｅｄＣａｔａｌｙｓｔｆｏｒＤｅｈｙｄｒｏｇｅｎａｔｉｏｎＥｔｈｙｌｂｅｎｚｅｎｅｔｏＳｔｙｒｅｎｅＺｈｕＹｉｘｉａｎｇ（祝以湘）；ＨｕＹｕｎｈａｎｇ（胡云行）（Ｃｏｌｌｅｇｅ...     

Effect of praseodymium additive on CeO_2(ZrO_2)/TiO_2 for selective catalytic reduction of NO by NH_3

A series of praseodymium added CeO_2(ZrO_2)/TiO_2 catalysts separately prepared by methods of sol-gel and impregnation were tested for selective catalytic reduction of NO, and characterized by X-ray diffraction(XRD), N_2-brumauer-emmett-teller(N_2-BET), NH_3-temperature programmed desorption(NH_3-TPD), H_2-temperature programmed reduction(H_2-TPR), PL spectra, Raman spectra, electron paramagnetic resonance(EPR) and X-ray photoelectron spectroscopy(XPS), respectively. Influence of preparation method on catalytic performance was studied. Results showed that the influence of Pr addition on catalytic performance of the CeO_2(ZrO_2)/TiO_2 catalysts was different between the sol-gel method and the impregnation method. The Pr addition tended to interact with TiO_2 and formed the structure of Ti-O-Pr in the sol-gel method while it was more likely to interact with CeO_2 forming the structure of Ce-O-Pr in the impregnation method. The total acid amount and redox properties of the catalysts prepared by sol-gel method decreased with the addition of Pr element, which resulted in decrease of catalytic activity. In contrast, the Pr-added catalyst prepared by impregnation method was found to possess easier reducibility, more total acid amount and higher proportion of Ce~(3+) species, which was favourable for higher catalytic activity.     

Application of rare earths in fluid catalytic cracking: A review

The need for more active and hydrothermally stable fluid catalytic cracking(FCC)catalysts to combat the effect of metal contaminants has led to an increase in demand for rare earth oxides.Rare earth oxides enhance catalyst activity and prevent the loss of acid sites during the FCC unit operation,especially when heavy residue with high metal content is used as feed.In this paper,a review was carried out to show the effects of rare earth elements on the structure,activity,and stability of FCC catalysts.Also,the use of rare earth elements as vanadium traps was analyzed in conjunction with the mechanism of catalyst deactivation by vanadium.The objective was to elucidate the interaction of vanadium species with the zeolite component of the FCC catalysts and the role of rare earth elements in countering the deleterious effects of vanadium on the FCC catalysts.     

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.     

Catalytic oxidation of CO on mesoporous codoped ceria catalysts:Insights into correlation of physicochemical property and catalytic activity

Codoping approach is an appealing strategy to further improve the catalytic activity of Ce-based catalysts. In the present study,Mn and/or Cu doped ceria solid solutions MnxCuyCe_(1-x-y)O_2,Cu_xCe_(1-x)O_2,Mn_xCe_(1-x)O_2 and pure CeO_2 were prepared by CTAB-assisted hydrothermal method for CO oxidation.XRD, SEM, EDS, BET, Raman, H2-TPR, XPS and in situ DRIFTS techniques were carried out to study the physicochemical properties and to correlate them to the activity. The doped samples maintain the cubic fluorite structure of CeO_2 with high crystallinity and small crystallite size, forming Ce-based solid solutions. The obtained catalysts have large mesoporous structure with average pore size of 10-14 nm. The doped transition metal enhances the oxygen vacancies and improves reducibility of the solids. The synergistic interaction of Mn and Cu codoping induces mo re oxygen vacancies, pro moting the increase of surface adsorbed oxygen and the transfer of bulk oxygen of catalyst, thereby enhancing the catalytic activity for CO oxidation. Besides, the decomposition rate of the carbonate species which is derived from in situ DRIFTS for each catalyst can provide a measure to evaluate its catalytic activity of CO oxidation.     

Cerium (Ⅳ) oxide nanocomposites:Catalytic properties and industrial application

This review article provides a new insight on the application of cerium oxide(CeO_2)-metal oxide nanocomposites as catalyst with enhanced reducibility and improved oxygen(O_2) storage capacity,especially in the varying chemical reaction processes including combustion,oxidation,epoxidation and redox.The CeO_2-metal oxide interaction plays an important role in controlling particle size,O_2 availability and coke resistance properties of the catalyst.Strong metal oxide-CeO_2 interaction also assists in generating small and highly dispersed particles,resists sintering of catalyst particles during the catalysis process,and consequently improves the O_2 availability of the catalyst.Indeed,CeO_2 not only provides an active support to heterogeneous catalyst,but also creates a new active site at the metal-support interface to produce stronger nanoparticle bonding through the surface O_2 vacancy.This consequently produces a heterogeneous catalytic system with promising reaction rate and catalytic stability in many industrial applications such as CO_2 hydrogenation,CO oxidatio n,biodiesel productio n,gas reduction,photocatalytic and methane steam reforming.     

稀土在汽车尾气净化中的应用

阐述了汽车尾气催化净化工艺中用稀土代替贵金属的必要性和可能性。叙述了三元（效）催化剂的类型和组成，稀土在三元催化剂中的作用及其应用前景和市场潜力。指出开发稀土三元催化剂并使之产业化有利于解决我国严重的环保问题，有利于我国稀土工业向高技术产业转轨。     

溴酸钾氧化甲基绿催化光度法测定痕量钯

研究了稀硫酸介质中痕量Ｐｄ（Ⅱ）催化溴酸钾氧化甲基绿的褪色反应及动力学条件，建立了高灵敏度测定痕量Ｐｄ（Ⅱ）的新催化光度法。方法的灵敏度为５６７×１０－１２ｇ／ｍｌ，线性范围为０～０１μｇ／２５ｍｌ。用于测定矿石中的痕量钯，结果较好。     

稀土在氨合成催化剂中的研究与应用

介绍了稀土在氨合成催化剂中的研究情况,重点综述了稀土的作用机理及催化性能,还介绍了国内稀土氨合成催化剂性能及工业应用情况。