等离子体制备稀土金属掺杂甲烷干气重整Ni/Mg/Al催化剂研究

采用冷等离子体炬技术制备了以水滑石为前驱体的Ni/Mg/Al催化剂,考察了La和Ce助剂的添加对催化剂结构及其对CH4和CO2重整催化性能的影响。利用XRD、BET、XPS及TG对催化剂进行了表征和性能测试。结果表明：冷等离子体炬能快速分解Ni/Mg/Al水滑石前驱体,生成具有介孔特性的水镁石相Mg(Ni,Al)O固溶体,并生成Ni0晶粒。在温度700℃,空速30000mL/(h·gcat), V（CH4）：V（CO2）=4：6的条件下,CH4和CO2的转化率分别为76%和61.8%。助剂Ce的添加增加了晶格氧,促进催化剂表面碳物种的消除,CH4和CO2的转化率分别提高了5%和7%。La的加入,抑制了Ni晶粒的团聚,增加了Ni的分散度,与未添加La的催化剂相比非活性碳的生成量减少70%,表现出良好的抗积炭性能。     

Ce助剂对负载型Ni/TiO_2催化剂CO甲烷化性能的影响

通过浸渍法制备了一系列20Ni/xCe-TiO_2催化剂。考察了助剂Ce对于NiO/TiO_2催化剂甲烷化性能的影响,并对Ce助剂的最佳添加量进行了研究。对所制得催化剂进行了活性评价、还原条件测试、寿命测试,并利用SEM对其进行了表征。结果表明,添加助剂Ce可以增加催化剂的使用寿命,提高催化剂分散性,减小催化剂晶粒大小,增加反应活性区间,提高CH_4的选择性。通过对助剂Ce不同添加量的研究发现,20Ni/6Ce-TiO_2催化剂的活性较好,CO转化率可达88.8%,CH_4收率可达99.3%。对20Ni/6Ce-TiO_2催化剂还原条件的研究表明,在500℃TPR还原条件下活性较优。     

Co/Mg/Al复合氧化物的制备与催化性能研究

分别采用共沉淀和水热法制备了一系列不同金属配比的Co/Mg/Al水滑石前驱体,经高温焙烧得到了Co/Mg/Al纳米复合氧化物,采用XRD和FTIR对其结构进行了表征。结果表明:Co/Mg/Al水滑石前驱体样品具有典型的水滑石层状结构,焙烧后得到了Co Al_2O_4尖晶石相和Mg O相。采用氮氧化物分析仪评价了其同时去除NOx和PM的催化活性。结果表明:反应温度和合成方法对NO转化率影响不大,Co/Mg/Al-LDO纳米催化剂在200~450℃的范围内均表现出较稳定的催化活性,在反应20 min后,NO的转化率趋于稳定。对于不同金属配比的催化剂,NO的转化率顺序为:Mg_2Al_1-LDOCo_1Mg_1Al_1-LDOCo_2Al_1-LDO,NO的转化率分别约为71.5%,44.5%和34.5%。     

MOx/Al2O3（M=Ni、Mg、Co、Ce）催化剂氟化预处理过程的物相转变和HFC-134a裂解制三氟乙烯性能

采用沉积沉淀法制备了MOx/Al2O3(M=Ni、Mg、Co、Ce)催化剂,研究了不同助剂对催化剂反应性能的影响,应用X射线衍射(XRD)考察了氟化预处理前后MOx/Al2O3催化剂中Al物种的转变,并应用于HFC-134a(1,1,1,2-四氟乙烷)裂解制备三氟乙烯(TrFE)反应。结果表明,Ni、Co、Ce添加能有效提高AlF3催化剂的HFC-134a裂解性能,而Mg对AlF3催化性能起抑制作用。其中,NiFx/AlF3催化剂催化性能最高,当反应温度为400℃时,HFC-134a的转化率最高可达21.4%,三氟乙烯的选择性在99.7%以上,且反应较为稳定。     

CO_2-O_2重整CH_4反应制备合成气的催化剂研究

针对CO_2-O_2联合重整CH_4反应制备合成气的催化剂进行了研究。首先以Zr、Ce无机盐为前体,采用溶胶-凝胶法和分步浸渍法制备ZrO_2-CeO_2载体,然后运用浸渍法制备负载型Ni催化剂,对载体的制备方法、焙烧温度、Ce/Zr比例及不同的活性组分对催化剂性能的影响进行了研究,再用BET和XRD等技术对催化剂进行表征。结果表明:在550℃下焙烧载体,以浸渍法制备的Ce/Zr=1/2,Ni负载量为9%的催化剂Ni/ZrO_2-CeO_2用于CH_4重整反应,可获得较高的转化率和稳定性。     

载体改性对Ni基催化剂分解四氢呋喃的影响

利用等体积浸渍法制备了不同金属改性载体的Ni/M_xO_y-Al₂O₃（M:Mg、La、Ce）催化剂,以四氢呋喃（THF）为模型化合物,对Ni/M_xO_y-Al₂O₃催化剂催化降解THF制氢活性进行评价。结果表明,添加助剂Ce、La、Mg后,THF转化率分别提高了12.7%、32.8%和31.0%。利用N₂物理吸附、X射线衍射（XRD）和氢气程序升温还原（H₂-TPR）等方法对不同载体的Ni/M_xO_y-Al₂O₃催化剂进行表征。结果表明,La、Ce、Mg的添加减弱了NiO与载体的相互作用,使得催化剂还原温度降低;La、Mg的氧化物高度分散于催化剂表面,但CeO₂-Al₂O₃复合载体在2θ为28.6°和56.3°处出现了CeO...     

复合镍基催化剂表面纳米团簇结构的调控及其催化应用

利用新型等离子体技术,将常压放电冷等离子体炬应用于催化剂制备,研究了制备方法、载体、活性组分和助剂对复合镍基催化剂表面纳米团簇结构的调控效果;并分析了催化剂表面纳米团簇结构的形成机理和催化剂性能的构效关系。结果表明:采用冷等离子体炬直接焙烧还原可调控表面纳米团簇;以-γAl2O3为载体的Ni催化剂(PCR)具有较高的活性和稳定性;活性组分Ni对表面纳米团簇结构的调控效果较好,添加量为12%(质量分数)时,表面纳米团簇高度分散,其尺寸约5 nm;助剂Mg添加可有效提高催化剂活性,合适的添加量为1%,且催化剂仍保持良好的表面纳米团簇结构,尺寸约5 nm;表面纳米团簇结构优化后的催化剂抗积炭能力明显提高。     

Ni-Mn/Al_2O_3催化剂在浆态床中CO甲烷化催化性能

采用共浸渍法制备了Ni-Mn/Al2O3催化剂,考察了助剂Mn的含量对催化剂结构及浆态床CO甲烷化性能的影响。采用XRD、H2-TPR、BET、TEM、H2-化学吸附等表征对催化剂进行了测试分析,结果表明,Mn助剂的引入能够促进Ni物种在载体表面的分散,减弱Ni物种与载体的相互作用,降低催化剂的还原温度,提高催化剂的比表面积,减小活性金属Ni的晶粒尺寸。随着Mn含量的增加,Ni-Mn/Al2O3催化剂的甲烷化性能先升后降,其中以Mn含量为4%(质量分数)时的催化甲烷化性能最佳,添加过量的Mn导致活性组分Ni被部分覆盖,催化甲烷化性能下降。通过对16Ni4Mn/Al2O3催化剂样品的浆态床反应温度及反应压力的研究发现,当反应温度为280℃、反应压力为1.5 MPa时,催化剂样品16Ni4Mn/Al2O3的CO转化率及CH4选择性分别达到96.2%和88.8%。     

助剂对Ni/Al2O3催化剂在石油树脂加氢过程中抗硫性能的影响

考察了助剂Mg、Fe和Cu的加入对抑制Ni/Al2O3催化剂中Ni晶粒的增长及加入助剂的催化剂在石油树脂加氢中抗硫性能的影响,结果表明,加入少量助剂能够抑制Ni/Al2O3催化剂中Ni晶粒的长大,同时助剂的加入也有助于催化剂加氢性能的提高,但助剂的加入量也影响催化剂的加氢性能,应根据催化剂性能适当加入剂的量。     

镍基负载合成NiO-Ce_xZr_(1-x)O_2/Al_2O_3催化剂的正交试验分析

采用正交试验探讨了制备方法、助剂配比以及焙烧温度三因素对合成催化剂、CH_4/CO_2重整反应催化性能的影响,采用BET手段进行催化剂表征。结果表明,对CH_4/CO_2反应性影响最大的是助剂的配比,其次是焙烧温度和制备方法。当助剂n(CeO_2)∶n(ZrO_2)=3∶1、采用沉淀-浸渍法、700℃焙烧温度时,甲烷和二氧化碳的转化率最高;经10h活性测试,CH_4、CO_2转化率和H2收率分别可达88.3%、81.2%和94.8%。     

Polymorphism of LiGa5O8 and of LiGa5O8-MgGa2O4Solid Solutions

High-temperature X-ray diffraction and differential thermal analyses showed that LiGa₅O₈ 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 LiGa₅O₈ 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 MgGa₂O₄ is present. The subsolidus equilibrium relations in the system MgGa₂O₄-LiGa₅O₈ are discussed.     

Magnetoresistance of CuxCo1-xFe2O4 Ferrites

Magnetoresistance measurements (Δ/R) were carried out on Cu _x Co_{1- x} Fe₂O₄ 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 μ_D 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.     

Sintering of Si3N4-Y2O3-Al2O3

Sintering kinetics of the system Si₃N4-Y2O₃-Al₂O3 were determined from measurements of the linear shrinkage of pressed disks sintered isothermally at 1500° to 1700°C. Amorphous and crystalline Si₃N₄ were studied with additions of 4 to 17 wt% Y₂O₃ and 4 wt% A1₂O₃. 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 ' -Si₃N₄ and glass or β '-Si₃N₄, α '-Si₃N₄, and glass. The compositions and amounts of the residual glassy phases are estimated.     

Expansive properties of the mixture C4ASH12 − 2CS III. Effects of temperature and restraint

The effects of temperature and restraint upon the hydration and the expansion of $\text{C}{}_4\text{A}\text{S}\text{H}{}_{12}\text{? 2}\text{C}\text{S}$ 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 $\text{C}{}_4\text{A}\text{S}\text{H}{}_{12}$ 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.     

Raman Study of Glasses of Ba2TiSi2O8 and Ba2TiGe2O8

Raman spectra are reported for fresnoite (Ba₂Ti(Si,Ge)₂O₈ glasses, and comparison is made between the Raman spectra of the corresponding crystalline powders and glasses of Ba₂TiSi₂O₈ and Ba₂TiGe₂O₈. The Ba₂TiGe₂O₈ glass spectra show correspondence with the Ba₂TiGe₂O₈ 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 Ba₂TiGe₂O₈ glass as revealed by a strong band at 824 cm⁻¹ in the I glass spectrum. The Ba₂TiSi₂O₈ glass spectra are similar to the Ba₂TiSi₂O₈ 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 Ba₂TiSi₂O₈ glass has a structure similar to the crystalline phase.     

Preparation and properties of poly(Nε,Nε-dicarboxymethyl-l-lysine)

A new ampholytic homopolypeptide, $\text{poly}\text{(N}{}^{\mathrm{\epsilon }}\text{,N}{}^{\mathrm{\epsilon }}\text{-}\text{dicarboxy-methyl-}\text{l}\text{-lysine}\text{)}$, 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 ($\text{q =}\text{[}\text{Cu}{}^{\mathrm{2+}}\text{]}\text{[}\text{residue}\text{]}$) 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.     

Effects of metal-support interactions on the hydrogenation of CO over PdSiO2 and PdLa2O3

A study of CO hydrogenation over $\text{Pd}\text{SiO}{}_2$ and $\text{Pd}\text{La}{}_2\text{O}{}_3$ 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 H₂O₂ 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 $\text{Pd}\text{SiO}{}_2$ 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 $\text{Pd}\text{La}{}_2\text{O}{}_3$ 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 $\text{Pd}\text{SiO}{}_2$ and $\text{Pd}\text{La}{}_2\text{O}{}_3$, for dispersions between 10 and 20%. On the other hand, the methane turnover frequency is independent of Pd dispersion over $\text{Pd}\text{SiO}{}_2$, but increases with decreasing dispersion over $\text{Pd}\text{La}{}_2\text{O}{}_3$. It is further observed that the Pd morphology influences the specific activity of $\text{Pd}\text{La}{}_2\text{O}{}_3$ for methanol synthesis: Pd(100) is nearly threefold more active than Pd(111). For a fixed morphology, the specific methanol synthesis activity of $\text{Pd}\text{La}{}_2\text{O}{}_3$ is a factor of 7.5 greater than that of $\text{Pd}\text{SiO}{}_2$.     

In situ laser raman spectroscopy of the sulfiding of Moγ-Al2O3 catalysts

Raman spectra of sulfided $\text{Mo}\text{γ-}\text{Al}{}_2\text{O}{}_3$ catalysts were obtained using in situ techniques for two sulfiding methods. For samples sulfided by 10% $\text{H}{}_2\text{S}\text{H}{}_2$ at 400 °C, MoS₂ structures were observed. A stepwise sulfiding using 10% $\text{H}{}_2\text{S}\text{H}{}_2$, 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 MoS 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.     

Wet Milling of Fe/Al/Al2O3 and Fe2O3/Al/Al2O3 Powder Mixtures

Wet milling of Al₂O₃-aluminide alloy (3A) precursor powders in acetone has been investigated by milling Fe/Al/Al₂O₃ and Fe₂O₃/Al/Al₂O₃ 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 Fe₂O₃/Al/Al₂O₃ powder mixtures were observed, the formation of a nanocrystalline, ordered intermetallic FeAl phase in Fe/Al/Al₂O₃ 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.