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1.
《高校化学工程学报》2015,(6)
分别采用体相模板法和表面模板法制备了铜改性Ce O_2催化剂(Cu O-Ce O_2和Cu O/Ce O_2)。利用XRD、N2吸附-脱附、Raman、H2-TPR对催化剂进行了表征并考察了其催化氧化HCl制Cl2的性能。结果表明:体相模板法更有利于制备铜物种分散度更高的催化剂,提高催化剂表面氧空位的浓度。将催化剂表面氧空位浓度与HCl催化氧化活性关联发现,催化剂氧空位浓度是影响HCl催化氧化活性的重要因素。酸洗前后催化剂催化活性对比表明,高分散的Cu O在较低温度时对催化剂活性贡献不大,而在较高温度时可以有效促进催化剂催化性能。晶相Cu O对HCl的催化氧化活性没有贡献。 相似文献
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以γ-Al2O3为催化剂载体,铜、锰为活性组分,稀土元素铈为助催化剂,采用浸渍法制备复合氧化物催化剂5%Cu/γ-Al2O3、5%Mn/γ-Al2O3、5%Cu-5%Mn/γ-Al2O3和5%Cu-5%Mn-1.6%Ce/γ-Al2O3,并考察其催化氧化甲苯性能。研究表明,复合氧化物催化剂催化氧化甲苯具有显著的效果,5%Cu-5%Mn/γ-Al2O3催化剂和5%Cu-5%Mn-1.6%Ce/γ-Al2O3催化剂表现出良好的低温活性和催化性能,对甲苯的完全燃烧温度分别为340℃和285℃。采用SEM和BET对催化剂进行表征,结果表明,催化剂的催化活性与活性组分在催化剂表面的分散度和催化剂的孔结构相关。 相似文献
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优先氧化是去除富H2中CO最有效的方法,铜铈催化剂是该领域的研究热点。以SBA-15为模板剂,采用纳米刻蚀法合成系列介孔Cu Ce/M/Cu Ce(M=Co,Mn,Zr)催化剂,采用XRD、N2吸附-脱附、TEM、H2-TPR和O2-TPD对催化剂结构及形貌进行表征,并对其在富H2中CO优先氧化性能进行研究。结果表明,Mn有利于催化剂表面吸附氧的增加,有助于大量氧空位的产生,进而促进CO优先氧化性能的提高;Zr的加入抑制了Cu O的还原,且其表面氧脱附温度范围过宽,不利于催化剂催化氧化性能的释放。掺杂Co与Mn可以形成Ce-Cu-M-O固溶体,促进了催化剂表面氧和晶格氧之间的相互转化,最终有利于铜铈催化剂CO优先氧化性能的提高。 相似文献
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将Co、Mn、Co-Mn、Co-Mn-Ce分别负载于Al_2O_3上,得到Co/Al_2O_3、Mn/Al_2O_3、Co-Mn/Al_2O_3、Co-Mn-Ce/Al_2O_3等4种催化剂,在30~75℃的条件下对臭氧氧化甲苯反应进行催化,比较了4种催化剂对臭氧氧化甲苯的催化效果。结果表明,复合催化剂Co-Mn/Al_2O_3的催化效果优于单组分催化剂Co/Al_2O_3、Mn/Al_2O_3,75℃时,甲苯降解率达到69.02%;添加助剂Ce的复合催化剂Co-Mn-Ce/Al_2O_3(Co∶Mn∶Ce=1∶1∶0.1,物质的量比)的催化效果最好,75℃时,甲苯降解率达到82.95%。 相似文献
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采用碳酸盐共沉淀法在全范围内制备了一系列具有高比表面积的铜锰互相掺杂的复合氧化物,通过调变铜锰摩尔比考察了其在甲苯催化燃烧反应中的表现。铜锰复合氧化物催化剂,尤其是掺杂低浓度铜的氧化锰,在甲苯催化燃烧中表现出了超越单组分氧化物的性能。随掺杂量的变化,反应活性呈现火山状的趋势。XRD、H2-TPR、XPS及BET等表征结果显示氧化物粒子的结晶度及分散度、催化剂的可还原性、表面氧浓度、催化剂的比表面积等诸多因素均对催化活性产生了一定的影响,然而复合氧化物催化性能上升的根本原因在于铜物种和锰物种之间存在的较强的相互协同作用。 相似文献
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在Caterpillar微反应器中采用共沉淀法制备了不同铜锰比的共沉淀物,直接焙烧得到铜锰复合氧化物催化剂。采用X射线衍射(XRD)、热重分析(TG)、拉曼光谱(Raman)和X射线光电子能谱(XPS)对沉淀物和催化剂进行了物相和结构分析。结果显示,随着Cu含量的增加,催化剂中Mn3+所占比例逐渐下降,表面晶格氧含量呈现先上升后下降的趋势,催化甲苯降解的活性呈现先上升后下降的规律。微反应器中的流动反应特性使得催化剂中的Cu、Mn保持良好分散性,有利于提高催化剂中Mn3+含量,此时表面晶格氧成为催化活性的制约因素。 相似文献
7.
采用沉积-沉淀法制备CuMnO_x/TiO_2新型甲苯燃烧催化剂,考察焙烧温度、Cu与Mn物质的量比、Cu和Mn总负载量、空速及水蒸汽含量对催化甲苯燃烧性能的影响。研究表明,焙烧温度500℃和Cu与Mn物质的量比为1∶1时,催化剂活性最好,反应温度250℃时,甲苯去除率为100%;水蒸汽的出现明显降低了甲苯转化率。XRD和H2-TPR表征结果表明,CuMnO_x/TiO_2催化剂的主要活性相为铜锰尖晶石(Cu1.5Mn1.5O4),它的存在降低了CuMnO_x/TiO_2催化剂的还原温度,是催化活性优良的主要原因。 相似文献
8.
采用氧化还原共沉淀法制备系列不同配比的锰铈复合氧化物,用于CO和CH4催化氧化,考察不同焙烧温度对催化剂性能的影响。研究表明,焙烧温度500℃和Mn与Ce物质的量比为5∶5的催化剂具备最优的CO和CH4催化氧化性能。催化剂在90℃时,CO转化率可达100%;对于CH4催化氧化,反应温度500℃时,CH4转化率为80%。通过N2吸附-脱附、H2-TPR和XRD等研究其物化结构性能,结果表明,在系列催化剂中,焙烧温度500℃和Mn与Ce物质的量比为5∶5的催化剂具有最高的比表面积和最活泼的晶格氧,可能是其具有优异催化活性的原因。 相似文献
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11.
R. K. DATTA 《Journal of the American Ceramic Society》1971,54(5):262-265
High-temperature X-ray diffraction and differential thermal analyses showed that LiGa5 O8 exists in two polymorphs related by the first-order transition at 1138°±3°C of the low-temperature simple-cubic form, space group (probably) O7 , to the high-temperature spinel (fcc) form, space group O h 7 . The transition is rapid, and the high-temperature form in pure LiGa5 O8 could not be quenched to room temperature under the conditions used. However, the high-temperature polymorph can be quenched under equilibrium conditions when 40 mol% or more MgGa2 O4 is present. The subsolidus equilibrium relations in the system MgGa2 O4 -LiGa5 O8 are discussed. 相似文献
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Ahmed A. Ghani Ali I. Eatah El-Mozamel El-Faramawy 《Journal of the American Ceramic Society》1988,71(12):492-C
Magnetoresistance measurements (Δ/R) were carried out on Cu x Co1- x Fe2 O4 samples with x =1, 0.75, 0.50, 0.25 and cobalt ferrite in the range of magnetic intensity (H) from 1.0 to 4.5 kG. Linear plots were obtained between log (Δ/R) and log H for all compositions except that of cobalt ferrite. The values of n at x =0.5 do not agree with the results of some authors. The discrepancy may be attributed to the value of magnetic field intensity at which such measurements were carried out. The similarity of features of n and μD with composition leads us to believe that the magnetoresistance may arise from the scattering of conduction electrons by localized electrons involving the s-d exchange interaction. 相似文献
14.
Sintering kinetics of the system Si3 N4-Y2O3 -Al2 O3 were determined from measurements of the linear shrinkage of pressed disks sintered isothermally at 1500° to 1700°C. Amorphous and crystalline Si3 N4 were studied with additions of 4 to 17 wt% Y2 O3 and 4 wt% A12 O3 . Sintering occurs by a liquid-phase mechanism in which the kinetics exhibit the three stages predicted by Kingery's model. However, the rates during the second stage of the process are higher for all compositions than predicted by the model. X-ray data show the presence of several transient phases which, with sufficient heating, disappear leaving mixtures of β ' -Si3 N4 and glass or β '-Si3 N4 , α '-Si3 N4 , and glass. The compositions and amounts of the residual glassy phases are estimated. 相似文献
15.
The effects of temperature and restraint upon the hydration and the expansion of mixture compacts in different contact solutions have been investigated. Temperatures above 20°C do apparently hinder the formation of an impervious felt-like layer of ettringite around the particles, thus greatly reducing the retarding effect of the lime. An uniaxial restraint of 1 Kg/cm2 is enough to reduce sensibly the expansions which remain however high (about 100%). The results can be satisfactorily interpreted by the reaction and expansion mechanism hypothesized in our previous papers. 相似文献
16.
Steven A. Markgraf Shiv K. Sharma Amar S. Bhalla 《Journal of the American Ceramic Society》1992,75(9):2630-2632
Raman spectra are reported for fresnoite (Ba2 Ti(Si,Ge)2 O8 glasses, and comparison is made between the Raman spectra of the corresponding crystalline powders and glasses of Ba2 TiSi2 O8 and Ba2 TiGe2 O8 . The Ba2 TiGe2 O8 glass spectra show correspondence with the Ba2 TiGe2 O8 crystalline Raman spectra; the v s (Ge–O–Ge) mode occurs at 518 cm−1 in the glass and at 521 cm−1 in the crystalline material. Five-fold coordinated titanium is the majority species present in the Ba2 TiGe2 O8 glass as revealed by a strong band at 824 cm−1 in the I glass spectrum. The Ba2 TiSi2 O8 glass spectra are similar to the Ba2 TiSi2 O8 crystalline spectrum; the strongest band is found at 836 cm−1 in the I glass spectrum. Through comparison with the previous Raman data of other titania silicate glasses, we conclude that the Ba2 TiSi2 O8 glass has a structure similar to the crystalline phase. 相似文献
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A new ampholytic homopolypeptide, , which has one tertiary amino and two carboxyl groups in the side chain has been derived from a hydrochloride salt of poly(L-lysine). The polymer in aqueous solution seems to be in the coil form with locally extended structure (LES) at neutral pH. In both the acidic and alkaline regions, the molar ellipticity of the polymer changes as a result of change in net charge on the side chain. The conformational changes may be from the coil with LES to other coiled forms. 5–7 M NaClO4 and 80% aqueous methanol induce the α-helix in the polymer at neutral pH. Divalent cations, Cu2+ and Ca2+, do not induce any remarkably ordered structures such as α-helix or β-structure in the polymer in aqueous solution at any pH. Ultraviolet absorption studies show an absorption peak of the polymer-Cu2+ complex near 240 nm. Dependence of the peak intensity on pH at various q values () indicates the two steps of the complex formation. At q less than 0.64, the formation is described only with the first step. An average coordination number for Cu2+ at the first step was calculated to be about 2 by the method of Mandel and Leyte. The association constant of Cu2+ with the residue at the step was determined from the absorption data to be far smaller than that for the Cu2+-EDTA complex. The second step of the formation occurs in the case of large q but the absorption data for the second step cannot be obtained exactly due to precipitation. 相似文献
18.
A study of CO hydrogenation over and has been carried out for the purpose of identifying the effects of Pd dispersion, Pd morphology, and support composition on the catalytic activity of supported Pd. The specific activity of each catalyst for methanol and methane synthesis was determined from microreactor studies carried out at a fixed set of reaction conditions. Palladium dispersion was measured by H2O2 titration, and the morphology of the Pd crystallites, as expressed by the distribution of Pd(100) and Pd(111) planes, was determined from in situ infrared spectra of adsorbed CO. The crystallite morphology of the catalysts is the same, independent of Pd weight loading: 90% of the surface is comprised of Pd(100) planes and 10% of the surface is comprised of Pd(111) planes. By contrast, the crystallite morphology of the catalysts changes with Pd loading. Primarily Pd(100) planes are exposed at low-weight loadings while Pd(111) planes are exposed at high-weight loadings. The Pd dispersion has little effect on the methanol turnover frequency over both and , for dispersions between 10 and 20%. On the other hand, the methane turnover frequency is independent of Pd dispersion over , but increases with decreasing dispersion over . It is further observed that the Pd morphology influences the specific activity of for methanol synthesis: Pd(100) is nearly threefold more active than Pd(111). For a fixed morphology, the specific methanol synthesis activity of is a factor of 7.5 greater than that of . 相似文献
19.
Silvia Schicker Daniel E. García Igor Gorlov Rolf Janssen Nils Claussen 《Journal of the American Ceramic Society》1999,82(10):2607-2612
Wet milling of Al2 O3 -aluminide alloy (3A) precursor powders in acetone has been investigated by milling Fe/Al/Al2 O3 and Fe2 O3 /Al/Al2 O3 powder mixtures. The influence of the milling process on the physical and chemical properties of the milled powders has been studied. Particle refinement and homogenization were found not to play a dominant role, whereas plastic deformation of the metal particles leads to the formation of dislocations and a highly disarranged polycrystalline structure. Although no chemical reactions among the powder components in Fe2 O3 /Al/Al2 O3 powder mixtures were observed, the formation of a nanocrystalline, ordered intermetallic FeAl phase in Fe/Al/Al2 O3 powder mixtures caused by mechanical alloying was detected. Chemical reactions of Fe and Al particle surfaces with the atmosphere and the milling media lead to the formation of highly porous hydroxides on the particle surfaces. Hence the specific surface area of the powders increases, while the powder density decreases during milling. The fraction of Fe oxidized during milling was determined to be 0.13. The fraction of Al oxidized during milling strongly depends on the metal content of the powder mixture. It ranges between 0.4 and 0.8. 相似文献
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Raman spectra of sulfided catalysts were obtained using in situ techniques for two sulfiding methods. For samples sulfided by 10% at 400 °C, MoS2 structures were observed. A stepwise sulfiding using 10% , with spectra recorded at 150, 250, and 350 °C, resulted in observation of molybdenum oxysulfide, reduced molybdate, and surface “MoS2” phases. Reexposure of these samples to air led to radical modification of the oxysulfide structures as well as transformation of some sulfide phases. A model incorporating terminal and bridging MoS bonding and anion vacancies is proposed. This model is based on the conversion of isolated and aggregated molybdate and MoO3 species to oxysulfide and reduced molybdenum phases. Conversion of reduced molybdenum phases to sulfides is observed to be slow. 相似文献