乙醇裂解协同制备氢气和碳纳米管

以乙醇为碳源,采用浸渍法制备的担载量为Fe(5%)/C催化剂,利用化学气相沉积法协同制备碳纳米管和氢气,分析了裂解温度(500⁸00℃)对于产生氢气产率和碳纳米管品质的影响。对于Fe(5%)/C催化裂解乙醇,最佳的反应温度为600℃,碳管的品质较好,氢气的产率最高为75%,生成的碳管为多壁碳纳米管。     

化学气相沉积法低温制备氢气和多壁碳纳米管

采用低温化学气相沉积法裂解乙醇协同制备氢气和多璧碳纳米管,乙醇作为碳源,Ni/C用作催化剂。考察反应温度和Ni/C比例对氢气的产率和碳纳米管品质的影响。多壁碳纳米管结构与组成通过扫描电镜、投射电镜和X射线粉末衍射进行表征。结果表明:Ni/C催化剂最佳Ni担载量为8%,最佳的反应温度为500℃,最佳条件下氢气的产率为79%,碳纳米管的品质最佳。     

氢气流量和反应时间对焦化苯裂解制备碳纳米管的影响

以工业级焦化苯为碳源,以二茂铁为催化剂前躯体,以噻吩为生长促进剂,采用催化裂解(CVD)法制备碳纳米管,通过TEM进行形貌表征,着重探讨氢气流量和反应时间对碳纳米管形貌和产率的影响。结果分析表明:氢气流量和反应时间在一定范围内增加时,所得碳纳米管的管壁直,缺陷少,纯度高,且纯化后产率增加。因此,通过控制氢气流量和反应时间可以控制碳纳米管的形貌,而且能够提高碳纳米管的产率。     

甲烷氧化制合成气LaFeO3催化剂的制备条件考察

采用溶胶-凝胶法制备了钙钛矿型复合氧化物LaFeO3,考察了合成过程中LaFeO3凝胶形成温度、催化材料焙烧温度、焙烧时间、络合剂种类、镧源种类以及氨基乙酸与硝酸根离子比对催化剂结构及性能的影响.结果发现催化剂最佳制备条件为:凝胶形成温度75 ～85℃;焙烧温度在900℃;焙烧时间10 h;氨基乙酸作络合剂;La2O3作为镧源;氨基乙酸与硝酸根离子比4∶3.     

高分子塑料催化裂解制备碳纳米管的研究进展

综述了近年来以塑料为原料,采用催化裂解法制备碳纳米管(CNTs)的研究现状,重点对比了催化剂种类对CNTs长度、管径及催化机制等方面的影响,并提出了聚合物催化裂解法制备碳纳米管研究中存在的问题和今后可能的发展方向。     

Fe-Mo/MgO催化剂CVD法制备碳纳米管

研究了Fe-Mo／MgO催化剂裂解乙炔制备碳纳米管的反应条件。结果表明,反应气氛对碳纳米管的生长具有明显的影响,在Hz或Ar气氛下,所得碳纳米管的质量较差,而在N2-H2(1：1体积比)和Ar-H2(5．5：1体积比)气氛下乙炔裂解可制得纯度好、收率较高的碳纳米管。电镜观察发现在Ar-H2气氛下所制备碳纳米管的直径(平均直径为18nm)明显小于在N2-H2气氛下所制备碳纳米管(平均直径为30nm),这便于通过反应气氛的调节来控制碳纳米管的直径。用Fe-Mo／MgO做催化剂、乙炔为碳源,Ar-H2反应气氛下．850℃左右、反应30min所得碳纳米管的质量、产率最佳。     

铁基碳纳米管复合材料的制备研究

利用催化裂解法成功地制备了铁基碳纳米管复合材料,并研究了制备温度、丙酮流速对碳纳米管生长的影响规律。试验采用场发射扫描电子显微镜对样品进行了表征与分析。研究结果表明:丙酮流速对碳纳米管的生长有重要影响,碳纳米管的质量随丙酮流速的提高均呈现出先提高后降低的规律。当制备温度为700℃,丙酮流速为2 m L/min时,制得的铁基碳纳米管复合材料碳纳米管分布均匀、与基体结合良好,此试验条件下碳纳米管的生长为顶部生长机理。但铁基碳纳米管复合材料的韧性、可塑性等性能还有待于进一步研究。     

新型稀土固体超强酸SO42-/MnO2/La3+的合成研究

以硫酸锰和硝酸镧为原料,采用共沉淀-浸渍法制备不同比例的SO^2-₄/MnO₂/La³⁺。以催化合成乙酸苄酯为探针反应,考察H₂SO₄浓度、La（NO₃）₃的质量分数、焙烧温度、焙烧时间等因素对其催化活性的影响。结果表明,催化剂制备的最佳条件为:硝酸镧的加人为硫酸锰的3%（质量分数）,浸渍浓度为1 mol·L^-1的H₂SO₄,焙烧温度为450℃,焙烧时间3 h,酯化率到达最大,为89.7%。     

煤裂解和气化过程中焦油裂解的实验研究

在热解和气化过程中产生的焦油 ,影响系统的正常运行 ,分析了煤热解和气化过程中温度、停留时间、压力、气氛、粒径以及床料等对焦油热裂解和催化裂解产生的影响 .同时 ,对比了不同催化剂的催化能力 .采用石灰石为催化剂 ,在 1 MW热态实验台上进行了实验 ,研究焦油和煤气成分在循环煤气作气化剂时不同钙硫比工况下的变化情况 .结果表明 ,石灰石的加入降低了焦油产率 ,提高了煤气产率 ,改善了煤气质量 .     

植物油脂裂解催化剂的合成及其催化性能研究

选用典型的高含油光皮树果实,采用等体积浸渍法制备固体碱催化剂KF/CaO催化裂解制备生物燃料油,并通过FTIR、XRD、SEM、CO2-TPD等对催化剂进行表征。对催化裂解后气相产率、液体油产率和固相产率的变化来验证催化剂的催化性能,考察催化剂用量、裂解反应时间和裂解反应温度对产物产率的影响。实验结果表明,在催化剂用量1.2%、反应温度500℃、反应时间为45min的条件下,实测生物燃料油产率可以达到82.56%。     

Ferroelectric Ceramics in the PbMg1/3Nb2/3O3-PbCd1/3Nb2/3O3 System

Solid solutions (1-x)PbMg_1/3Nb_2/3O₃ + xPbCd_1/3Nb_2/3O₃ with x = 0-0.30 are investigated with purpose to work out a capacitor ceramics with good dielectric properties and low sintering temperature. It is found that the perovskite phase forms at sintering near to 980°C and begins to decompose at higher temperatures. When x grows from 0 to 0.30, the Curie temperature linearly grows from -10°C to +25°C, the dielectric permittivity ε_m in the Curie point T_C decreases from 18000 to 6800 and the phase transition becomes more diffused. The dielectric permittivity at room temperature is rather high and the temperature stability is improved. The system is of interest, because it can serve as a base for working out some ceramic materials for capacitors with low sintering temperature, which needs of no special atmosphere at burning.     

Sintering of glass-added BaZn1/3Nb2/3O3 ceramics

The complex perovskite oxide Ba(Zn_1/3Nb_2/3)O₃ (BZN) has been studied for its attractive dielectric properties which place this material interesting for applications as multilayer ceramics capacitors or hyperfrequency resonators. This material is sinterable at low temperature with combined glass phase–lithium salt additions, and exhibits, at 1 MHz very low dielectric losses combined with relatively high dielectric constant and a good stability of this later versus temperature. The 2 wt.% of ZnO–SiO₂–B₂O₃ glass phase and 1 wt.% of LiF-added BZN sample sintered at 900 °C exhibits a relative density higher than 95% and attractive dielectric properties: a dielectric constant ?_r of 39, low dielectrics losses (tan(δ) < 10⁻³) and a temperature coefficient of permittivity τ_? of 45 ppm/°C⁻¹. The 2 wt.% ZnO–SiO₂–B₂O₃ glass phase and 1 wt.% of B₂O₃-added BZN sintered at 930 °C exhibits also attractive dielectric properties (?_r = 38, tan(δ) < 10⁻³) and it is more interesting in terms of temperature coefficient of the permittivity (τ_? = −5 ppm/°C). Their good dielectric properties and their compatibility with Ag electrodes, make these ceramics suitable for L.T.C.C applications.     

Dielectric and Piezoelectric Properties of Pb(Co1/3Nb2/3)O3-PbTiO3-PbZrO3 Solid Solution Ceramics

Ceramic and piezoelectric properties of the Pb(Co_1/3Nb_2/3)O₃-PbTiO₃-PbZrO₃ system were investigated. The system contains rhombohedral, tetragonal, and pseudocubic phases at room temperature. The triple point is at 0.07Pb(Co_1/3Nb_2/3)O₃-0.43PbTiO₃-0.50PbZrO₃. High dielectric constants (750 to 1500) and radial coupling coefficients (40 to 45%) and low average temperature coefficients of resonant frequency (of the order of 10^-6°C) were obtained for compositions near the morphotropic phase boundary.     

Sintering Behavior and Surface Microstructure of PbO-Rich PbNi1/3Nb2/3O3–PbTiO3–PbZrO3 Ceramics

The sintering behavior and surface microstructure of PbNi_1/3Nb_2/3O₃–PbTiO₃–PbZrO₃ (PNiNb-PT-PZ) ceramics were investigated. The PNiNb-PT-PZ ceramics with the stoichiometric composition and the addition of excess lead oxide (PbO-rich ceramics) were sintered by liquid-phase sintering in accordance with the solution-reprecipitation mechanism at temperatures below the melting point of PbO. The temperature at which the liquid phase forms fell to near the eutectic point of the PbO–Nb₂O₅ and the PbO–TiO₂ system (868°C) with the addition of 5 mol% PbO. As the calcination temperature influenced the sinterability of the stoichiometric PNiNb-PT-PZ ceramic, unreacted PbO was considered to be the source of the liquid phase in the sintering of the stoichiometric powder. The secondary phase was observed at the surface of PbO-rich ceramics and was suggested to be a liquid phase expelled from inside the ceramic. A sintering scheme of PNiNb-PT-PZ ceramics was proposed, and the high sinterability of PNiNb-PT-PZ ceramics was attributed to the low formation temperature of the liquid phase.     

Effect of the hydrogen spillover on the selectivity of dibenzothiophene hydrodesulfurization over CoSx/γ-Al2O3, NiSx/γ-Al2O3 and MoS2/γ-Al2O3 catalysts

Dibenzothiophene (DBT) hydrodesulphurization (HDS) reaction at 3 MPa and 325–375 °C on Mo/γ-Al₂O₃ single-bed and Me/γ-Al₂O₃//SiO₂//Mo/γ-Al₂O₃ (Me = Co or Ni) double-bed catalysts were investigated. Results indicate that ratio cyclohexylbenzene (CHB)/biphenyl (BP) or selectivity is higher when using double-beds rather than a single-bed. Synergy in dibenzothiophene hydrodesulphurization on Co//Mo and Ni//Mo double-beds is also detected. Changes in selectivity and conversion are attributed to the action of spillover hydrogen (Hso) formed in the first bed that reaches the second bed.     

Low-Temperature Synthesis of 0.65 PbMg1/3Nb2/3O3–0.35PbTiO3 Ceramics

Nanocrystalline 0.65 PbMg_1/3Nb_2/3O₃–0.35PbTiO₃ powders were synthesized by citrate gel method. The gel was prepared using citrate (titanium and niobium) and nitrate (lead and magnesium) salts. The hard gel obtained after completion of the reaction was treated to get the desired phase. Thermal analysis of the gel was done to optimize the calcination temperature. The calcined powders were characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The crystallite size and the effective strain were found to be 50 nm and 0.03584 N, respectively.     

Electromechanical Testing and Modeling of a Pb(Mg1/3Nb2/3)O3-PbTiO3-BaTiO3 Relaxor Ferroelectric

Compressive prestress effects on the electrical and mechanical properties of relaxor ferroelectric materials were studied as a function of temperature for several formulations of Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃-BaTiO₃ (PMN-PT-BT) ceramics. Experimentally measured polarization and strain, induced by an ac electric field, decreased as compressive stress increased. Effective Young's moduli also were measured under constant dc electric fields. A significant decrease in modulus was observed with increasing field. The prestress and modulus experiments were modeled analytically using a proposed relaxor ferroelectric constitutive law. In general, excellent agreement between the model and experiments was obtained, indicating that the model accurately predicted the coupled behavior of this relaxor ferroelectric material.     

Electric properties of polycrystalline PbCd1/3Nb2/3O3

Temperature dependence of dielectric permittivity and electric conductivity of polycrystalline PbCd_1/3Nb_2/3O₃ in the region of phase transition have been presented. Electric properties of polycrystalline PbCd_1/3Nb_2/3O₃ depend on frequency of the measuring field. In the region of para-ferroelectric phase transition a change of electric properties takes place.     

Structure Evolution from Pb(Mg1/3Nb2/3)O3 to La(Mg2/3Nb1/3)O3

The crystal structure of lanthanum-modified lead magnesium niobates having composition (Pb_{1− x} La _x ) (Mg_{(1+ x )/3}-Nb_{(2− x )/3})O₃ with X = 0 to 1 was investigated by X-ray powder diffraction. It was found that the fundamental reflections from perovskite structure remain in the whole range of composition. The superlattice reflections from the A(B'_1/2-B"_1/2)O₃ ordered structure are also well preserved for La content greater than 50 at.%; however, a series of extra peaks of mixing indices appears, with intensities gradually enhanced with the increase of La content. For the complete substitution of Pb by La, a splitting of some reflections can be observed in the diffraction pattern. The results indicate that the crystal structure evolves continuously with the La content, from disordered cubic perovskite of space group Pm 3 m for X = 0, to ordered cubic perovskite of space group Fm 3 m for X = 0.5, distorted cubic perovskite of space group Pa 3 for 0.5 < X < 0.9, and finally to a rhombohedral perovskite, possibly belonging to the space group R 3 , for X ≥ 0.9. In the evolution of structure, a linear reduction of the lattice constant of the perovskite cell from 4.048 to 3.964 Å was observed.