EFFECT OF REDUCTION CONDITIONS ON THE ACTIVITY OF Ni/γAl2O3 CATALYST FOR METHANATION REACTION

The effect of reduction conditions, mainly reduction temperature and duration time on the activity of Ni/γAl₂O₃ catalyst were studied for a methanation reaction in a gradientless Berty reactor. The methanation reaction was investigated using a feed containing CO (6.7 mole%), H₂ (26 mole%) and the balance being nitrogen at a pressure of 30 psig and a fixed temperature of 350°C. The reduction temperature was varying from 250 to 500°C, in order to investigate its effect on the methanation reaction. The methanation activity of the catalyst increased to a maximum by increasing the reduction temperature up to a maximum at 300-350°C and showed a slight negative decline afterward. The second parameter investigated was reduction duration time which was varied from 2 to 16 hours. It was observed that the methanation reaction activity increased by increasing the reduction duration time up to 6 hours. After six hours, there was no increase in activity. Based on the finding of this investigation, a recommended set of reduction conditions is given: reduction temperature of 300°C and a duration time of six hours.     

SELF-SUSTAINED OSCILLATIONS DURING CO OXIDATION ON A Pt/γ-Al2O3 CATALYST

A systematic study of the effect of reaction environment and catalyst surface on self-sustained oscillations during CO oxidation on a Pt/γ-Al2O, catalyst is presented in this paper. The catalyst, consisting of a fixed bed of small particles, was subjected to three different pretreatments: fresh, O2 - H2 treated and poisoned by SO2. Self-sustained oscillations, lasting for as long as desired, were manifest in a narrow range of temperatures and O2/CO ratios. The structure of the oscillatory pattern varied with catalyst pretreatment, however, in all cases the predominant feature consisted in transitions between low and high conversion levels (ignition-quenching). The amplitude and frequency of the oscillations varied with surface pretreatment, however, they decreased as temperature and O2:/CO ratio increases. Small temperature fluctuations of less than 6°C, which mirrowed concentration oscillations were also observed. A unique feature observed under certain conditions, was an overshoot of CO2 outlet concentration in excess to the 100% conversion, which indicated the participation of surface stored CO. The results are discussed in terms of competitive CO and O2 adsorption-reaction coupled with reactor and surface balances.     

SIMULTANEOUS REACTIONS OF CO, NO, O2 AND NH3 ON Pt/γA12O3 CATALYST IN A TUBULAR REACTOR

A reliable method to continuously monitor NH₃ in a gas stream containing CO—NO—O₂ and H₂O has been developed. The method is based on a quantitative oxidation of NH₃ to NO on a Pt catalyst. The extent of this reaction is affected by temperature, excess oxygen present, and space-velocity. There is a significant effect of inlet O₂ concentration on extent of various reactions in the CO—NO—O₂—H₂O system on a Pt/γAl₂O₃ catalyst. At fixed space-velocity and catalyst temperature, and for fixed reactor inlet concentrations of CO and NO. there is negligible CO—NO reaction either in the absence of oxygen or in the presence of excess oxygen. However, short of the stoichiometric amount of O₂ required for CO oxidation, there is appreciable CO—NO (and possibly also CO—NO—H₂O) reaction whose extent increases with increasing oxygen concentration. This increase is especially dramatic in a narrow window of O₂: concentrations near the stoichiometric point. Interestingly enough, near the stoichiometric point, self-sustained isothermal oscillations in the outlet CO and NO concentrations are also observed (Subramaniam and Varma. submitted for publication)     

显微Raman光谱法对Al2O3-SiO2-H2O系反应过程的探索表征

用显微Raman光谱法在Al2O3-SiO2-H2O体系不除去所含水分的情况下对样品进行了检测,避免了脱水处理过程对样品微结构的损伤.研究了反应产物和微结构随时间进展的变化情况,对同一样品进行了定点跟踪观察,Raman光谱检测结果和在显微镜下观测结果很好地对应.结果表明:对于配比为m(钾水玻璃):m(偏高岭土):m粉煤灰): m(硅灰)=10:9:1:1,石膏掺量为3.7%的实验样品,在搅拌后4 h之内,二水石膏溶解于体系,Ca2 浓度提高,[SiO4]4-聚合度下降,偏高岭土中的五配位铝逐渐消失;在搅拌后4h至1 d中,大量的含水凝胶物形成,材料也因此开始有强度,样品表面变得致密;在搅拌后1 d至7d中,结晶态K2SO4形成,样品表面致密程度大幅提高,材料的强度也随之提高.     

Al2O3/NiAl复相陶瓷料浆流变性的研究

本文主要对Al2 O3 NiAl复合体系料浆的稳定分散特征作了初步研究。结果表明 :对Al2 O3和NiAl单体系 ,当溶液的pH >10 .6时 ,颗粒表面的 ζ电位达到最大值 ;当料浆中Al2 O3含量在 40wt %以上时 ,其稳定分散的最佳pH范围为 11～ 12 ,当料浆浓度为40vol%、5 0vol%和 60vol %时 ,最佳分散剂用量分别为 0 .6%、2 .8%和 8.0 % ;对浓度小于 3 0vol %的NiAl料浆 ,最佳pH范围为 9～ 11,分散剂最佳用量为 0 .5 % ;在最佳分散条件下制得的 5 0vol % (Al2 O3 NiAl-2 0 )的复相陶瓷料浆具有良好的稳定分散性     

Al2O3/SiC复合陶瓷的反应烧结

在空气中于1600℃对Al2O3/0.78%SiC纳米复合体进行2h的反应烧结,制得Al2O3/5%莫来石复合陶瓷,其中的莫来石分为两类,即3Al2O3·2SiC和Al5.65Si0.35O9.175。采用SEM和TEM研究Al2O3/莫来石复全陶瓷的微观结构。对Al2O3/莫来石复合陶瓷的密度和力学性能如杨氏模量、泊松比、硬度、韧性和强度进行了研究。     

THE FLOW BEHAVIOR OF SUBMICRON α-Al2O3 AQUEOUS SUSPENSIONS

The viscosity of aqueous, charged a-Al₂O₃ suspensions with and without added polyelectrolytes (polyacrylic acid (PAA 1800)) is investigated over a wide range of volume fractions and shear rates. The Carreau-Yasuda model is used for both cases for examining the shear-rate dependence; for the electrostatically-stabilized suspensions the Krieger-Dougherty and Quemada models are used to determine the maximum packing fraction. The latter analysis shows that the suspension behavior changes from liquid-like to solid-like at a volume fraction of 0.71 in the low-shear limit and at 0.89 at the high-shear limit (because of the polydispersity of the suspension). The results with polyelectrolytes indicate that the dosage of the polymer plays an important role in the viscosity of suspensions and that there is an optimum dosage of polyelectrolyte that must be added to reduce the viscosity at high volume fractions of solids.     

高分散度催化剂Pt／Mg（Al）O与Pt／Al_2O_3化学吸附H_2、CO和CO_2的性能比较

比较了制法完全相同并有相近铂分散度（Ｈ／Ｐｔ≈１１）的催化剂Ｐｔ／Ｍｇ（Ａｌ）Ｏ与Ｐｔ／Ａｌ２Ｏ３的性质。由Ｈ２和ＣＯ的化学吸附以及随之使用的红外光谱及微量热计测定了它们的Ｐｔ的性质，并由ＣＯ２的程序升温脱附（ＴＰＤ）技术测定了Ｍｇ（Ａｌ）Ｏ的碱性基点的性质。在沉积了Ｐｔ颗粒后Ｍｇ（Ａｌ）Ｏ的表面碱性降低。与Ｐｔ／Ａｌ２Ｏ３相比，Ｐｔ／Ｍｇ（Ａｌ）Ｏ在１９６０１９３０ｃｍ－１出现了一个新的ＣＯ红外吸附波带，它被认为是ＣＯ通过碳原子与Ｐｔ键合并通过氧原子与Ｍｇｎ＋阳离子键合的一种桥键。这些桥键的物质在高温脱附时最稳定。ＣＯ的歧化作用发生在Ｐｔ／Ｍｇ（Ａｌ）Ｏ，所生成的ＣＯ２迁移至载体的碱性基点形成碳酸盐。     

Al2O3-ZrO2系共晶组成研究

配制了Al2O3-ZrO2系含ZrO2的质量分数分别为25%,30%,35%,40%,45%和48%的6个组成的试样于电炉中熔融并快速冷却.借助SEM-EDAX研究了试样的显微结构,结果表明:在含ZrO2的质量分数为25%～40%的试样中可观察到初晶刚玉和细卵状共晶相组成;在含ZrO2的质量分数为45%～48%的试样中可观察到初晶ZrO2相和细卵状共晶显微结构.借助于EDAX测定了含ZrO2的质量分数为40%和45%两试样的共晶组成,其结果为含ZrO2的质量分数为43.3±0.4%.     

铝镁浇注料钢包衬渣线部位Al_2O_3-ZrO_2-SiO_2系陶瓷保护涂层的研究

以铝镁浇注料钢包衬为母体，主要研究渣线部位预防性Ａｌ２Ｏ３－ＺｒＯ２－ＳｉＯ２系陶瓷保护涂层作用机理，以期钢包各部位寿命同步，进而提高其寿命节材降耗。通过试验，取得了可喜的进展。     

核化温度对CaO-Al2O3SiO2系微晶玻璃晶化行为的影响

利用DTA技术测定了某一配方的CaO-Al2O3SiO2系玻璃的玻璃转变温度 (Tg)与玻璃晶化温度(Tp),在Tg温度稍上,进行了不同温度的预核化处理.经预核化处理后的试样的DTA和SEM分析结果表明,随预核化温度的增加,晶化峰向低温方向移动,表明析晶能力在增强.在晶化温度稍上热处理,玻璃表面析晶,玻璃从表面到内部长成粗大的柱状晶,并以树枝状方式生长.在玻璃内部,尺寸细小的等轴晶镶嵌在玻璃相中.     

Interactions NO—CO and O2—NO—CO on CuCo2O4/γ-Al2O3 and on γ-Al2O3- and CuCo2O4/γ-Al2O3-supported Pt, Rh and Pt—Rh catalysts, a transient response study

The interactions NO—CO and O₂—NO—CO have been studied onCuCo₂O₄γ-Al₂O₃ and on γ-Al₂O₃- and CuCo₂O₄γ-Al₂O₃-supported Pt, Rh and Pt—Rh catalysts. The deposition of noble metals (Pt, Rh and Pt—Rh) on CuCo₂O₄γ-Al₂O₃ instead of γ-Al₂O₃ is beneficial in: lowering the temperature at which maximum N₂O is formed and decreasing the maximum N₂O concentration attained; lowering the onset temperature of NO to N₂ reduction, and increasing the N₂ selectivity; preserving the activity towards NO to N₂ reduction on a higher level following the concentration step NO + COO₂+ NO + CO and changing the conditions from stoichiometric to oxidizing (50% excess of oxidants). The reason for this behaviour of the CuCo₂O₄γ-Al₂O₃-based noble metal catalysts is the formation (reversible) of a reduced surface layer on the CuCo₂O₄ supported spinel under the conditions of a stoichiometric NO + CO mixture.     

Al2O3／TiB2陶瓷材料的高温摩擦磨损特性研究

研究了Ａｌ２Ｏ３／ＴｉＢ２陶瓷材料与硬质合金往复滑动摩擦时，在不同氢气和温度条件下的摩擦磨损特性，结果表明：随温度和气氛不同，材料的摩擦系数有着不同的变化规律。在高温空气气氛中摩擦时，ＴｉＢ２氧化生成的表面氧化膜可起到固体润滑剂的作用，并且能阻止Ｃｏ的扩用，减轻粘着，因而能降低摩擦系数并有利于提高材料的耐磨性能；而在高温氮气气氛中摩擦时，由于硬质合金中的Ｃｏｐ扩散到陶瓷材料中，使材料产生粘着磨损和     

在Pt／Al2O3催化剂上气相苯加氢反应的动力学

在研制得到了高活性和高选择性 Pt/Al_2O_3催化剂的基础上,采用微反-色谱联用装置考察了气相苯加氢反应的动力学。假定在催化剂表面上存在着两种不同的活性中心,一种吸附氧;另一种吸附苯、环己烷及反应中间物,并假定吸附氢与吸附苯间的表面反应为过程的控制步骤,从而导出动力学方程。通过实验测得了不同反应条件下的反应速率和组分分压,并用非线性回归方法处理实验数据,求得方程中各参数。通过偏差分析、方差分析及 Boudart 提出的四条判断准则,验证了动力学模型及回归参数的合理性。结果得到了此动力学模型与实验数据较好地吻合。在此基础上测定了反应的活化能及氢、苯和环已烷的吸附热。     

Al2O3/BN复相陶瓷的R曲线特性

采用压痕-强度法测定了Al2O3／BN复相陶瓷的阻力曲线。结果表明;该复相陶瓷具有良好的耐接触损伤性能,呈现出上升的阻力曲线效应,显示出增强的抗裂纹扩展能力。而对应的Al2O3单相陶瓷的阻力曲线为一水平直线。分析认为：超细弥散的h—BN与基体之间模量及热膨胀失配会在h—BN的弱结合层间产生微开裂,有助于抑制主裂纹的失稳扩展,这是Al2O3／BN复相陶瓷具有优良耐损伤性能和上升型R曲线效应的主要原因。     

Al2O3陶瓷的动态力学性能研究

本文采用ＳＨＰＢ装置对９５瓷、９７瓷和９９瓷的动态力学性能进行实验研究。结果表明Ａｌ２Ｏ３陶瓷在高冲击载荷下其抗压强度增高,其增加幅度随Ａｌ２Ｏ３含量增加而加大,并分析了机理。     

Y2O3-Al2O3粉体固相反应制备Y-Al-O体系陶瓷的对比研究

研究了摩尔比n(Y2O3):n(Al2O3)分别为2:1、1:1和3:5的粉体在不同温度发生的相变及其高温烧结的陶瓷。Y2O3-Al2O3粉体经球磨后在1750℃真空烧结制备陶瓷。用差热-热重、X射线衍射及扫描电子显微镜表征制备的Y2O3-Al2O3材料。结果表明:在低于800℃时,Y2O3-Al2O3之间未发生反应;在1000℃煅烧后,出现Y4Al2O9(YAM)相;1200℃煅烧后,出现YAlO3(YAP)相和钇铝石榴石(yttrium aluminumgarnet,YAG)相。n(Y2O3):n(Al2O3)=3:5粉体在1400℃煅烧后生成YAG纯相。n(Y2O3):n(Al2O3)=2:1、3:5粉体烧结的陶瓷的物相分别为YAM相和YAG相,其相对体积密度分别为97.8%和99.95%,n(Y2O3):n(Al2O3)=1:1粉体烧结陶瓷的物相为多相共存,3种配比制备陶瓷断口的形貌差别较大。     

Co－Mo／MgO－Al_2O_3一氧化碳耐硫变换催化剂失活原因的探讨

采用程序升温硫化（ＴＰＳ）技术，微反—色谱法（ＭＲＣ）、扫描电镜、透射电镜和其它分析测试手段，对工业应用前后的Ｃｏ－Ｍｏ系耐硫变换催化剂Ｋ８－１１进行了分析，从而对其失活原因进行了分析和讨论     

Al2O3/Al2O3扩散连接机理的研究

采用热压方式进行氧化铝陶瓷材料的扩散连接，并深入探讨了其连接机理，结果表明：采用适当的连接工艺，可使此种材料产生塑性形变，接触面积增加，空洞收缩和闭合，扩散进行充分，1420℃，15MPa热压60min条件下，获得的最高强度为357MPa，超过母材强度平均连接强度为250MPa，是母材平均强度的85％。