新型纳米V_2O_5催化剂的制备与表征

以片状工业V2O5晶体为原料,采用Sol-gel法制备含纳米V2O5颗粒的溶胶和凝胶,并以此胶体为活性组分、硅藻土为载体制得一种新型纳米钒催化剂,研究了催化剂的显微结构和性能。结果表明,经过酸洗处理后的硅藻土的物理化学性质满足催化剂载体要求,TEM和SEM研究显示,胶体中V2O5颗粒形貌呈现针状或球状,催化剂中的活性组分V2O5颗粒大小仍然处于纳米级别且分散均匀,纳米钒催化剂的强度为61.3N.cm-1,活性达87.4%。     

纳米V_2O_5催化剂的制备工艺实验研究

用精制硅藻土作载体、V2O5胶体为钒源、K2SO4和硫磺粉为助剂,制备负载型纳米V2O5催化剂,探讨了V2O5用量、K2SO4用量、硫磺用量和焙烧温度对催化性能的影响。结果表明,V2O5用量影响非常显著,硫磺粉用量和焙烧温度影响较为显著,K2SO4用量为10%¹6%时影响不明显。催化剂制备最佳工艺条件为:硅藻土∶V2O5∶K2SO4∶硫磺粉=100∶7∶16∶7(质量比),焙烧温度800℃。     

V_2O_5/TiO_2催化剂上NH_3选择性催化还原NO反应动力学研究

采用浸渍法制备了V2O5/TiO2催化剂,研究了V2O5/TiO2催化剂上NH3选择性催化还原NO的反应动力学,运用Eley-Rideal机理模型确定了相关的动力学参数,推导出本征动力学方程,得到反应的活化能为41.9 kJ/mol。     

纳米V_2O_5催化剂的制备工艺实验研究

用精制硅藻土作载体、V2O5胶体为钒源、K2SO4和硫磺粉为助剂,制备负载型纳米V2O5催化剂,探讨了V2O5用量、K2SO4用量、硫磺用量和焙烧温度对催化性能的影响。结果表明,V2O5用量影响非常显著,硫磺粉用量和焙烧温度影响较为显著,K2SO4用量为10%~16%时影响不明显。催化剂制备最佳工艺条件为:硅藻土∶V2O5∶K2SO4∶硫磺粉=100∶7∶16∶7(质量比),焙烧温度800℃。     

V_2O_5-WO_3/TiO_2催化剂的制备

采用工业钛白粉作为烟气脱硝催化剂的载体原料,通过添加助剂M对其改性,研制出了一种V2O5-WO3/Ti O2烟气脱硝催化剂,并确定助剂M的最佳量为质量分数10%;同时考察了焙烧温度对该催化剂比表面积及脱硝性能的影响,确定了最佳焙烧温度为500℃;最佳活性组分钒含量为质量分数1.5%,稳定助剂钨含量为质量分数8%的催化剂性能最好。     

反相微乳法制备纳米V_2O_5

采用十六烷基三甲基溴化铵（CTAB）/正丁醇/正辛烷/水溶液微乳体系成功制备了纳米V2O5。先采用反相微乳法分别制备碱性偏钒酸铵微乳液和稀硫酸单相微乳液,再将两种微乳液混合得到V2O5前驱物,经陈化、洗涤、干燥、焙烧得到纳米V2O5。通过测定电导率分析了微乳体系的稳定性,采用FTIR、XRD、TEM对纳米V2O5的结构、成分、晶形、粒径等进行了表征。结果表明,采用反相微乳法制备的纳米V2O5为球形、分散性较好、颗粒粒径为6～20nm。     

新型钒系固体超强酸S_2O_8~（2-）/V_2O_5催化剂的制备研究

以NH4VO3为原料,（NH4）2S2O8为浸渍液,添加一定量Fe2O3,用沉淀-浸渍法制备出新型S2O82-/V2O5-Fe2O3固体超强酸催化剂。以合成乙酸苄酯作为探针反应,考察不同制备条件下超强酸的催化活性。研究发现,最优条件为：V2O5与Fe2O3的摩尔比为n（V2O5）∶n（Fe2O3）=1.0∶1.0,浸渍液浓度为1.5 mol/L,焙烧温度350℃,焙烧时间3 h效果最佳,催化剂的活性最好。     

制备方法对V_2O_5-WO_3/TiO_2选择性催化还原催化剂性能的影响

采用共沉淀法、溶胶-凝胶法和浸渍法制备了V2O5质量分数4%和WO3质量分数6%的V2O5-WO3/TiO2选择性催化还原催化剂,对比了3种方法制备的催化剂选择性催化还原NO性能。采用X射线衍射、热重、N2吸附-脱附和程序升温还原等对制备的V2O5-WO3/Ti O2催化剂的结构和性质进行表征,结果表明,共沉淀法制备的V2O5-WO3/TiO2催化剂具有更好的选择性催化还原NO活性和更大的比表面积,影响共沉淀法选择性催化还原NO活性的主要因素是催化剂的热稳定性、表面羟基数量、比表面积、粒径分布以及V、W与Ti之间的内在作用。     

Li~+离子嵌入V_2O_5干凝胶薄膜的XPS研究

V2 O5薄膜是最具有实用价值的全固态“灵巧窗”器件中候选锂离子储存材料之一。本研究采用熔融淬冷法成功制备了V2 O5溶胶 ,利用提拉法在ITO玻璃片上制备了表面均匀和无裂纹的V2 O5干凝胶薄膜 ,并采用电化学方法将Li+ 离子嵌入到V2 O5干凝胶薄膜中。本文着重采用X射线光电子能谱 (XPS)分析了Li+ 离子嵌入V2 O5干凝胶薄膜前后的化学组成及钒、氧、锂离子的化学状态     

V_2O_5-WO_3/TiO_2催化剂的制备及其烟气脱硝性能

以活性成分负载量、负载顺序和焙烧温度等关键制备参数因素进行正交实验设计制备了V_2O_5-WO_3/TiO_2催化剂,对其进行XRD和TPR表征,并在自行设计搭建的SCR烟气脱硝实验平台上评价其(300~390)℃的SCR脱硝性能。结果表明,活性成分钒和钨绝大多数以非晶态形式存在于载体表面,且具有良好的分散性;主要活性成分V_2O_5负载量越高,脱硝率越高;400℃焙烧温度可以形成催化反应所需的晶相,且维持催化剂较高的比表面积;催化剂低温活性和高温活性是由表面富集和各种成分之间相互作用共同产生的结果,活性组分与载体之间的相互作用对315℃低温脱硝活性影响明显,以先钒后钨负载顺序为宜,表面富集对390℃高温脱硝活性起主要作用,以钒钨同时负载或先钒后钨负载顺序较好;随着m(WO_3)∶m(V_2O_5)的增加,在7.5∶1处催化剂的脱硝率升至最高,随后迅速下降,WO_3负载质量分数以6%为宜。在优化条件V_2O_5负载质量分数0.8%、WO_3负载质量分数6%、先钒后钨负载和400℃焙烧温度下制备了催化剂并进行脱硝性能验证,315℃低温脱硝活性达到69.56%。     

Leaching Kinetics of Fe2Al5 and Skeletal Iron Formation

Caustic leaching of fine particles of Fe₂Al₅ alloy to produce skeletal Fe catalysts was studied using a 2⁴ factorial experimental design, in which alloy particle size, aqueous NaOH concentration, temperature and stirrer speed were varied. Analysis of the results from the design showed that the BET surface area of the skeletal iron increased with decreases in temperature, caustic concentration and particle size according to S_BET = 222.7 ? 0.461 · T ? 2.35 · c_NaOH ? 0.0245 · D _p. An Avrami–Erofeev model ?ln(1 ? α) = kt with an activation energy of 55 ± 5 kJ mol^?1 and a shrinking core model for volume contraction 1 ? (1 ? α)^1/3 = kt and an activation energy of 56 ± 5 kJ mol^?1 provided the best fit to the kinetic data for leaching.     

Formation of V2AlC MAX phase by SHS involving magnesium reduction of V2O5

Herein, the V₂AlC MAX phase was prepared by self-propagating high-temperature synthesis from V₂O₅/Mg/Al/C mixtures in molten NaCl salt and acid leaching of the as-synthesized product. The combustion process was performed in a stainless-steel chamber in the graphite boat under an argon atmosphere of 3 MPa. X-ray diffraction analysis was used to examine the phase composition of the products. During combustion synthesis, a multiphase powder product containing V₂AlC, VAl, VC and MgO, MgAl₂O₄ is formed. By adjusting the ratios of the initial materials, we determined that 26.6V₂O₅/28.2Mg/4.5Al/0.7C/40NaCl mixture resulted in the maximum V₂AlC yield without spinel impurity. The following acid leaching leads to the removal of VAl impurity and obtaining of a powder containing up to 95% V₂AlC. According to SEM analysis the powder is composed dominantly of flake-like grains. Thus, the choice of the available and low-cost precursor materials and the use of the energy-efficient SHS method allow for a drastic reduction in the production cost of the V₂AlC.     

Kinetics of Formation of a Platelet-Reinforced Ceramic Composite Prepared by the Directed Reaction of Zirconium with Boron Carbide

The kinetics of formation of a new class of ceramic composite material, zirconium diboride platelet-reinforced zirconium carbides, are discussed. These materials are prepared by the directed reaction of molten zirconium with boron carbide to form a ceramic material composed of zirconium carbide matrix containing a controlled amount of residual zirconium metal. Results from interrupted growth studies, differential thermal analysis, adiabatic reaction temperature calculations, and kinetic measurements have been used to study the kinetics of the process. The reaction is very fast and proceeds parabolic ally with time with a rate constant between 1.6 X 10^-2 and 3.9 X 10^-2 cm²/_s. The proposed mechanism suggests that when molten zirconium contacts boron carbide, the molten zirconium exothermically reacts with the boron carbide to form a boron-rich liquid. Further reaction is sustained by the continuous dissolution of the boron carbide as the boron-rich liquid is drawn into the boron carbide. The product is a zirconium carbiride/zirconium carbide/zirconium composite which homogenizes quickly at the reaction temperature to yield a uniform product microstructure throughout the composite. Two alternative rate-limiting steps are discussed and the implications of each are explored.     

Formation Mechanisms of Ti3SnC2 Nanolaminate Carbide Using Fe as Additive

Reactive sintering of 3Ti:Sn:2C and 3Ti:Sn:2C:0.6Fe powder mixtures is studied in the temperature range 510°C–1200°C under argon. It is demonstrated that the recently discovered Ti₃SnC₂ phase is formed, provided that Fe is added to a 3Ti:Sn:2C reactant mixture within the synthesis conditions used. Using dilatometric and X‐Ray diffraction analyses, the formation mechanism of Ti₃SnC₂ is discussed. Results show that at low temperature (about 510°C), tin is consumed to form Fe_xSn_y intermetallics. At high temperature (about 1060°C), tin is newly available to form Ti₃SnC₂ due to the melting of Fe_xSn_y. Then, the intermediate phases, TiC and Ti₂SnC, and/or Ti₅Sn₃, TiC, C, and Ti are dissolved in the (Fe + Sn) liquid phase and Ti₃SnC₂ very likely precipitate from the melt. The second part of the study deals with the optimization of the Fe content in the initial 3Ti:Sn:2C reactant powder mixture to synthesize samples with larger Ti₃SnC₂ content by hot isostatic pressing.     

铁矿石孔隙度对其还原和碳化铁生成的影响

在1023 K温度下用热重法结合XRD和EDX分析研究了70%H2-30%CH4混合气体还原铁矿石制备碳化铁的过程,测定了原矿和还原中间产物的微孔分布. 结果表明,相同反应条件下微观结构不同的铁矿石其还原速率和碳化速率有较大差别,巴西块矿、澳大利亚块矿及南非球团矿在50 min内都可以全部还原,此后生成碳化铁;而南非块矿则需90 min才能基本还原,此后没有碳化铁生成. 疏松多孔的铁矿石较致密铁矿石的还原速率快,生成的还原铁结构疏松,有利于碳化反应的进行. 铁矿石还原后,0.5~3.5 nm微孔孔容积率约提高2倍,分布规律与原矿石相似,3.5~13 nm的微孔孔容积提高显著,这些对还原速率和碳化铁的生成反应有较大影响.     

Phase equilibrium studies in V2O5-Fe2O3 and V2O5-TiO2 systems

V₂O₅-Fe₂O₃ and V₂O₅-TiO₂ systems represent two important chemical systems with various applications, including energy, catalysts, and high-performance materials. In the present study, high-temperature phase equilibrium experiments were conducted at the temperature range of 670–1000°C in air. Electron probe X-ray micro-analyzer (EPMA) was used to analyze the microstructure and composition of the phases presented in quenched samples. Systematic experiments demonstrated that V₂O₅-containing systems should not be quenched by water-based quenching media. Phase diagrams in both systems were constructed, and the eutectic and peritectic points of the systems were confirmed and compared with previous studies. The present study improved the previous results and could be used as the base for thermodynamic modelings and further applications of the two systems.     

V2O5负载量对V2O5／TiO2催化剂SCR法脱硝的影响

以TiO2载体,采用浸渍法制备了不同V2O5负载量的用于选择性催化还原NOx的V2O5／TiO2催化剂。利用BET,SEM和Ⅺ①,对不同V2O5负载量的催化剂组成、结构、形貌和性能进行了表征,考察不同V2O5负载量对催化剂制备的影响。结果表明制备的催化剂具有较多的中孔和微孔,催化剂中V2O5含量的增加,会降低催化剂的表面积;V2O5含量为2％的V2O5／TiO2催化剂样品比表面积最大,但是其活性非常低;V2O5含量为4％催化剂比表面积较大,NOx脱转化率高;V2O5的负载量小时,V2O5主要以等轴聚合的钒基型式（V3O7和V6O13）存在,这些钒基是催化剂的活性中心;当负载量超过6％,V2O5主要以结晶相存在,占据大量活性位,降低催化效果。     

活性炭还原五氧化二钒制备二氧化钒

以V2O5为原料,活性炭为还原剂,采用碳热还原法制备了VO_2。探讨了还原剂用量和反应时间对各价态钒氧化物质量分数的影响,采用化学滴定法、XRD、SEM和DSC分析了产品的纯度、物相、形貌和相变温度。结果表明:在V2O5和活性炭的物质的量比为2∶1、反应时间为5 h的条件下,所得产品纯度(以VO_2质量分数计)为99.6%,VO_2转化率达到93.9%。产品为M相VO_2,其颗粒细小(粒径为110μm)且结晶性良好。     

Al2O3-HZSM-5催化甲醇脱水制二甲醚的反应动力学

采用机械混合法制备了不同组成的Al2O3-HZSM-5复合固体酸催化剂,采用N2吸附和x射线衍射（XRD）等对催化剂结构进行表征,考察了催化剂在甲醇脱水制二甲醚反应中的活性并研究其反应动力学。结果表明,添加质量分数为20％的Al2O3（20％）-HZSM-5复合固体酸催化剂具有较好的反应活性,在该催化剂上进行甲醇脱水制二甲醚的反应符合Rideal-Eley分子吸附机理,根据实验数据计算得到甲醇脱水反应的活化能为38.42kJ／mol,指前因子为1171.3min^-1。     

V2O5/Al2O3上异丁烷脱氢反应研究

用浸渍法制备了质量分数为12%V₂O₅/Al₂O₃负载型催化剂，考察了催化剂的活化气氛，反应中异丁烷与氢气的比例和反应温度对异丁烷脱氢活性的影响。结果表明，用N2作活化气，反应中异丁烷与氢气的体积比为1∶1时，在质量分数为12%的V₂O₅/Al₂O₃催化剂上异丁烷脱氢转化率和选择性较好，在625 ℃时，转化率达到52%，选择性为80%。