Ni-Fe/BaTiO3-γ-Al2O3催化剂在低温条件下CO2和CH4重整中的应用

采用等体积浸渍法制备了一系列不同Ni和Fe添加量的Ni-Fe/BaTiO3/γ-Al2O3双金属催化剂,并在固定床反应装置上考察了在873～1 073 K温度范围内催化剂对CO2和CH4重整反应的催化活性。实验结果表明:Ni、Fe负载质量分数均为5.0%的Ni-Fe/BaTiO3/γ-Al2O3催化剂活性最好。通过TPR、TPD和TPO表征并与单金属催化剂Ni/BaTiO3/γ-Al2O3相比,Ni-Fe/BaTiO3/γ-Al2O3催化剂具有更高的催化活性、脱附和抗积炭性能。     

Ni-Co双金属催化剂在二氧化碳重整甲烷反应中的催化活性研究

采用等体积浸渍法制备了Ni/BaTiO3、Co/BaTiO3和Ni-Co/BaTiO3催化剂,并在固定床反应装置上考察了在973~1 073 K这些催化剂对CO2重整CH4反应的催化活性,且采用程序升温还原技术对催化剂进行表征,发现与单金属催化剂相比,Ni-Co/BaTiO3双金属催化剂有更为优越的催化活性。结果表明在Ni-Co/BaTiO3催化剂中Ni和Co之间产生了一定的协同作用。同时研究了不同的制备方法对Ni-Co双金属催化剂催化活性的影响,用溶胶-凝胶法制备的催化剂具有更高的催化活性。     

助剂MgO对甲烷二氧化碳重整Co/BaTiO3催化剂催化性能的影响

采用溶胶-凝胶法在Co/BaTiO3催化剂中引入助剂MgO,考察了其对甲烷二氧化碳重整Co/BaTiO3催化剂的催化反应性能的影响,利用X射线衍射仪(XRD)、H2程序升温还原(H2-TPR)对催化剂进行了表征,结果表明,助剂MgO使钴催化剂中的活性Co2O3组分增多,还原性和分散性能较好;在n(CO2)∶n(CH4)为1∶1、气相空速(GHSV)为12 000 h-1、反应温度为700℃的条件下,催化剂Co-MgO/BaTiO3表现出良好的催化性能,且反应初期甲烷转化率可达到94.87%,CO选择性可达85.21%,H2收率可达74.08%。     

载体对镍基催化剂CH4/CO2重整反应性能的影响

采用等体积浸渍法制备了Ni/BaTiO3、Ni/Al2O3和Ni/BaTiO3-Al2O3催化剂,对催化剂进行表征,并与催化剂活性相关联.发现与单一载体催化剂相比,具有适当比例组成的Ni/BaTiO3-Al2O3催化剂有更为优越的催化性能.结果表明Ni/BaTiO3-Al2O3催化剂有较大的比表面积;复合载体在制备过程中发生了反应,所生成的BaAl2O4可以阻止γ-Al2O3的相变并极大的提高了载体的热稳定性.     

光辐照驱动CH4/CO2催化重整制合成气

以等离子体还原制备的Ni/Al2O3和Ni/MgO-Al2O3为催化剂,用氙灯模拟太阳光聚光系统进行CH4-CO2重整反应,并考察其催化性能及能量转化效率,实验结果表明,以等离子体还原并加入MgO助剂制备的Ni/MgO-Al2O3催化剂具有较好的低温催化活性,在温度为740℃时,CH4和CO2的最高转化率分别为83.6 25%.1和%,能量转化效率为41.5%,大大高于光伏法制氢效率的10.85%;XRD表征表明,等离子体还原使催化剂活性组分Ni具有良好的分散性和更小的纳米团簇结构,有利于甲烷的转化;MgO助剂的加入增强了催化剂表面的碱性,促进了CO2的吸附和解离。     

镍基氨分解制氢催化剂的制备及性能

用浸渍法制备Ni/Al_2O_3和Ni/xMo-Al_2O_3催化剂,以氨分解为模型反应,考察Ni负载量、焙烧温度、溶剂和助剂等合成条件对催化剂催化性能的影响,通过XRD和TG-DTG表征方法对催化剂进行表征。结果表明,最佳合成条件:Ni负载质量分数为16%,焙烧温度350℃,采用丙酮为溶剂制备的Ni/Al_2O_3催化剂具有较好的催化活性。500℃添加质量分数3%的助剂Mo可以使Ni/Al_2O_3催化剂的活性显著提高39%,Ni/3%Mo-Al_2O_3催化剂的氨分解率达93.5%。     

La2O3助剂对Ni/γ-Al2O3/堇青石结构化催化剂催化加氢合成间苯二胺性能的影响

研究助剂La2O3对Ni/γ-Al2O3/堇青石结构化催化剂结构与性能的影响。采用悬浮液涂层法、活性组分浸渍法制备不同La2O3助剂含量的Ni/γ-Al2O3/堇青石结构化催化剂。通过BET、XRD、TPR、XPS对催化剂进行表征,发现不添加La2O3助剂时活性组分以NiAl2O4形式存在,添加La2O3助剂后则以NiAl2O4和NiO两种形式存在,易还原NiO的生成提高了催化剂的活性。添加La2O3助剂还能使催化剂的比表面积降低和孔尺寸增大,活性评价表明助剂La2O3存在适宜添加量,即La含量为3%。同时发现助剂La2O3对选择性的影响大于活性,La2O3具有结构助剂的特点。     

低浓度CH_4燃烧催化剂制备及其反应性能研究

采用化学共沉淀-凝胶工艺制备纳米γ-Al_2O_3载体,氧化钾(K_2O)、氧化镁(MgO)、氧化铈(CeO_2)为催化助剂,PdO为催化剂活性组分,浸渍法负载催化剂组分。研究了活化升温速率、助剂种类及助剂加入方式对催化剂性能的影响。结果表明,富氧气氛下经缓慢氧化活化后的催化剂表现出较高的活性;浸渍法添加助剂的催化剂活性高于共沉淀法加入助剂的催化剂;助剂K_2O、MgO和CeO_2均能够提高催化剂活性,除K_2O外,催化剂活性随着助剂的含量增加而增大,其中20%CeO_2的催化剂表现出较高的催化活性。     

过渡金属对Pt/SiC催化剂上CO氧化性能的影响

以SiC为载体、Pt为活性组分、过渡金属Fe、Co和Ni为助剂,采用浸渍法制备CO氧化催化剂。考察浸渍方法、助剂及其负载量、空速和催化剂焙烧温度等对Pt/SiC催化剂性能的影响。结果表明,助剂的加入提高了活性组分Pt在载体表面的分散度,并产生一定的相互作用,从而提高了催化剂活性,其中,铁助剂的助催化效果较好。共浸渍法制备的催化剂的催化活性优于分步浸渍法,Pt-Fe/SiC催化剂制备中焙烧温度500 ℃时,催化剂活性较佳,适量Fe助剂的添加能够显著提高Pt/SiC催化剂的活性。     

助剂对加氢催化剂Ni/SiO_2结构和反应性能的影响

采用等体积浸渍法制备了含不同助剂的m 二硝基苯液相催化加氢催化剂Ni/SiO2,利用BET、XRD、TPR和活性评价等方法对催化剂的物化性质和催化性能进行了研究,考察了不同助剂对催化剂结构和反应性能的影响。试验结果表明,向NiO/SiO2催化剂中引入La2O3、K2O及Li2O助剂后提高了催化剂中镍物种的分散度及还原能力,改善了催化剂的反应性能,其中以La2O3和K2O双助剂的作用最为明显。     

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.     

Activation and characterization of Fe---Mn---SO4/ZrO2 catalysts

Changes in Fe---Mn---SO₄²⁻/ZrO₂ catalyst formulations during activation have been observed. In air or an inert gas, the added salt, such as iron and/or manganese nitrate, decomposes over a temperature range of about 200–400°C to produce nitric oxide, oxygen and iron and/or manganese oxide. The crystallization of zirconia occurs at 450°C; when the sample contains sulfate the exothermic event occurs at a temperature that is about 200°C higher. Heating in the presence of hydrogen causes the evolution of nitric oxide to occur over a narrow temperature range and at a lower temperature than when the sample is heated in helium or air. It appears that the nitrate ions associated with Fe, Mn and Zr decompose to produce nitric oxide, and presumably water, at different temperatures when the sample is heated in the presence of hydrogen. Heating samples of sulfated zirconia containing iron and/or manganese in hydrogen causes sulfur evolution at a lower temperature, and a significant fraction of it in the form of H₂S.     

The structures of VOx/MOx and alkali-VOx/MOx catalysts and their catalytic performances for soot combustion

Vanadium oxides supported on γ-Al₂O₃, SiO₂, TiO₂, and ZrO₂ were studied on their molecular structures and reactive performances for soot combustion. To investigate the effect of different alkali metals on the structures and reactivities of supported-vanadium oxide catalysts, they were doped into the V₄/TiO₂ catalyst which had the best intrinsic activity for soot combustion in the selected supported vanadium oxide catalysts. The experimental results demonstrated that the catalytic properties of these catalysts depended on the vanadium loading amount, support nature, and the presence or the absence of alkali metals. The spectroscopic analysis (FT-IR and UV–vis) and H₂-TPR results revealed that the higher activity of alkali-promoted vanadium oxide catalysts could be related to the ability of alkali metal promoting the redox cycle of the active vanadyl species. TG results showed that adding alkali to V_m/TiO₂ catalyst was beneficial to lowering their melting points. Low melting points could ensure the good surface atom migration ability, which would improve the contact between the catalyst and soot. Due to the alkali metal components promoting the redox ability and the mobility of the catalysts, alkali-modified vanadium oxide catalysts could remarkably improve their catalytic activities for soot combustion. The catalytic activity order for soot combustion followed Li > Na > K > Rb > Cs in the catalyst system of alkali-V₄/TiO₂, and the reason why it followed this sequence was 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.     

Compact Swelling in Bi1.4Pb0.6Sr2Ca2Cu3.6Oy During the Formation of High-Tc Superconducting Phase

Compact swelling in Pb-doped Bi-Sr-Ca-Cu-O superconductor has been studied by observing the effects of the size of calcined powders, volatilization of materials, and sintering of high- T _c (2223) powders. The bulk density increases at the early stage of sintering, for about 20 h, and then decreases. Densification occurs when the low- T _c (2212) phase and a liquid phase exist, whereas dedensification occurs with the formation of the 2223 phase regardless of the presence of the liquid. Gas evolution from specimens does not appear to be responsible for compact swelling. Compact swelling is explained by anisotropic growth of thin, platelike 2223 grains in random orientation. When 2223 grains grow in a preferred direction, compact swelling is suppressed.     

Preparation of the High-Quality Superconductor La1Ba2Cu3Oy

The relationship between the preparation procedure and superconducting properties of La₁Ba₂Cu₃O_y was studied. A series of samples was sintered in an N₂-gas atmosphere for various lengths of time ranging from 1 to 40 h, followed by a fixed annealing procedure in O₂. It was found that the shorter the sintering period, the higher was the oxygen content. The samples sintered for a period of less than 15 h contained excess oxygen compared with La₁Ba₂Cu₃O₇ and exhibited poor superconducting properties. The sample sintered for 40 h had an oxygen content y equal to 6.95, and had excellent superconducting properties. The mechanism for preparing high-quality La₁Ba₂Cu₃O_y is discussed.     

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.     

Microwave Dielectric Properties of CaTiO3-CaAl1/2Nb1/2O3 Ceramics Doped with Li3NbO4

The microwave dielectric properties of CaTi_{1− x} (Al_1/2Nb_1/2) _x O₃ solid solutions (0.3 ≤ x ≤ 0.7) have been investigated. The sintered samples had perovskite structures similar to CaTiO₃. The substitution of Ti⁴⁺ by Al³⁺/Nb⁵⁺ improved the quality factor Q of the sintered specimens. A small addition of Li₃NbO₄ (about 1 wt%) was found to be very effective for lowering sintering temperature of ceramics from 1450–1500° to 1300°C. The composition with x = 0.5 sintered at 1300°C for 5 h revealed excellent dielectric properties, namely, a dielectric constant (ɛ_r) of 48, a Q × f value of 32 100 GHz, and a temperature coefficient of the resonant frequency (τ_f) of −2 ppm/K. Li₃NbO₄ as a sintering additive had no harmful influence on τ_f of ceramics.