What If the Protection against Oxidation of Chromia-Forming Alloys Was Not Always Due to the Chromia Layer?

Chromia-forming alloys have good resistance to oxidizing agents such as O2, CO2, … It is accepted that the protection of these alloys is always due to the chromia layer formed at the surface of the alloys, which acts as a barrier between the oxidizing gases and the alloy substrates, forming a diffusion zone that limits the overall reaction rate and leads to parabolic kinetics. But this was not verified in the study devoted to Inconel®625 the oxidation in CO2 that was followed by TGA, with characterizations by XRD, EDS and FIB microscopy. Contrary to what was expected and accepted in similar studies on other chromia-forming alloys, it was shown that the diffusion step that governs the overall reaction rate is not located inside the chromia layer but inside the alloy, precisely inside a zone just beneath the interface alloy/chromia, this zone being depleted in chromium. The chromia layer, therefore, plays no kinetic role and does not directly protect the underlying alloy. This result was demonstrated using a simple test that consisted in removing the chromia layer from the surface of samples partially oxidized and then to continue the thermal treatment: insofar as the kinetics continued without any change in rate, this proved that this surface layer of oxide did not protect the substrate. Based on previous work on many chromia-forming alloys, the possibility of a similar reaction mechanism is discussed. If the chromia layer is not the source of protection for a number of chromia-forming alloys, as is suspected, this might have major consequences in terms of industrial applications.

Effect of slag composition on corrosion resistance of high chromia refractory bricks for industrial entrained-flow gasifier

The slag composition corresponding to different coals varies significantly,which directly affects the operation of industrial entrained-flow gasifier and the service life of refractory bricks.In this study,the corrosion resistance of several typical coal slags for gasification on high chromia refractory bricks was comparatively investigated by static laboratory crucible tests and thermodynamic simulations.The results demonstrated that the corrosion degree of high chromia refractory bricks by different coal slags was high-Ca/Na slag>high-Fe slag>high-Si/Al slag.The surface structure of the refractory was relatively flat after corrosion by high-Si/Al slag,and the primary corrosion reaction was the partial dissolution of the matrix by the slag.High-Fe slag was prone to the precipitation of iron phases as well as the formation of(Mg,Fe)(Al,Cr)_(2)O_(4)composite spinel layer at the slag/refractory interface.The high-Ca/Na slag was susceptible to react with the refractory to yield a low melting point phase,which led to the destruction of the matrix structure of the refractory and an isolated distribution of particles.In addition,the monoclinic ZrO_(2) in the refractory reacted with CaO in the slag to formed calcium zirconate,which loosened its phase toughening effect,was the primary factor that aggravated the refractory corrosion.

Isobutane dehydrogenation over chromia alumina catalysts prepared from MIL-101: Insight into chromium species on activity and selectivity

Various mesoporous chromia alumina catalysts were prepared by five different methods based on a metal-organic framework MIL-101 and their catalytic performances over isobutane dehydrogenation were investigated. The highly dispersed chromium species were produced on catalyst KCrAI-I1 with largest specific surface area of 198 m2-g-1 prepared with aluminium isopropoxide （Al（i-OC3HT）3） by ultrasonic im- pregnation method. However, the catalyst KCrAI-I2 synthesized by stirring impregnation possessed crystalline a-Cr203 phase, which was poorly dispersed. Two types of Cr-rich and Al-rich CrzA12_zO3 solid solutions, designated as CrAI-I and CrAI-II phase, were formed over the catalysts KCrAI-I3 （prepared by Al（i-OC3HT）3 with nitric acid regulation）, KCrA1-C4 （prepared by aluminium chloride hexahydrate） and KCrA1-N5 （prepared by aluminium nitrate nonahydrate）. Catalytic evaluation results revealed that KCrAI-I1 exhibited the high isobutane con- version due to its highly dispersed chromium species. However, KCrAI-I3, KCrA1-C4 and KCrA1-N5 showed the higher isobutene selectivity （95.2%-96.4%） on account of the formation of chromia alumina solid solutions in the catalysts. Moreover, the solid solution over the chromia alumina catalysts could greatly suppress the coke formation.

Thermodynamic simulation of the effect of slag chemistry on the corrosion behavior of alumina–chromia refractory

The corrosion behavior of alumina-chromia refractory against two kinds of industrial slags （coal slag and iron smelting slag） at 1550℃ was investigated via thermodynamic simulations. In the proposed simulation model, the initial slag first attacks the matrix and surface aggregates and subsequently attacks the inner aggregates. The simulation results indicate that the slag chemistry strongly affects the phase formation and corrosion behavior of the refractory brick. Greater amounts of alumina were dissolved and spinel solid phases formed when the brick interacted with iron smelting slag. These phenomena, as well as the calculated lower viscosity, may lead to much deeper penetration than that exhibited by coal slag and to more severe corrosion compared to that induced by coal slag. The thermodynamic calculations well match the experimental observations, demonstrating the efficiency of the proposed simulation model for evaluating the corrosion behavior of alumina-chromia refractory.

Dehydrogenation of Isobutane to Isobutene with Carbon Dioxide over SBA-15-Supported Chromia-Ceria Catalysts

A series of SBA-15-supported chromia-ceria catalysts with 3% Cr and 1%--5% Ce （3Cr-Ce/SBA） were pre- pared using an incipient wetness impregnation method. The catalysts were characterized by XRD, N2 adsorption, SEM, TEM-EDX, Raman spectroscopy, UV-vis spectroscopy, XPS and H2-TPR, and their catalytic performance for isobutane dehydrogenation with CO2 was tested. The addition of ceria to SBA-15-supported chromia improves the dispersion of chromium species. 3Cr-Ce/SBA catalysts are more active than SBA-15-supported chromia （3Cr/SBA）, which is due to a higher concentration of Cr^6＋ species present on the former catalysts. The 3Cr-3Ce/SBA catalyst shows the highest activity, which gives 35.4% isobutane conversion and 89.6% isobutene selectivity at 570℃ after 10 min of the reaction.

Characterization and Dehydrogenation Activity of SBA-15 and HMS Supported Chromia Catalysts

SBA-15 and HMS supported chromia catalysts were prepared and characterized. Chromia is highly dispersed on the mesoporous supports when its loading is 7 wt%. The supported catalysts display high activity, selectivity and stability for dehydrogenation of ethylbenzene and propane. ESR measurement of the catalysts before and after reaction shows that the active species for dehydrogenation reaction might be Cr3+ species on the catalyst surface, and the activity of the catalyst is probably correlated with the dispersion of Cr3+ species.

Synthesis and characterization of chromia-pillared layered tetratitanate

The first chromia-pillared layered tetratitanate was prepared by the reaction of layered tetramethylammonium tetratitanate with chromium (III) acetate [Cr(OAc)3] aqueous solution and subsequent calcination of the resultant solid product in air at 400°C. The obtained chromia-pillared layered tetratitanate has an interlayer distance of 1.06 nm and a high thermal stability up to 600°C. It was also found that calcination in N2 led to the chromia-pillared layered tetratitanate with relatively higher Brunauer-Emmett-Teller (BET) specific surface area (93.9 m2·g?1) and smaller average pore diameter (4.44 nm) than that in air (82.0 m2·g?1, 7.61 nm). Both Br?nsted and Lewis acid sites (mainly Lewis type) are present on the chromia-Pillared layered tetratitanate (500°C, N2, 8 h) and strong enough to still remain a small proportion of pyridine upon outgassing at 250°C. Moreover, ammonia temperature-programmed desorption (NH3-TPD) result showed that there were three NH3 desorption peaks at 160, 200 and 315°C, respectively. The corresponding acid amount is 41.3, 73.9 and 290.7 μmol·g?1. The total acid amount is 405.9 μmol·g?1.

金属铬添加量对刚玉质耐火材料性能的影响

为了获得抗热震性好、使用寿命长的刚玉质耐火材料,以粒度为5~3、3~1、≤1、≤0.044 mm的白刚玉为主要原料,金属铬(≤0.074 mm)为添加剂制备刚玉质耐火材料。研究了金属铬添加量(质量分数分别为0、1%、3%和5%)对刚玉质耐火材料物理性能、抗热震性以及抗渣侵蚀性能的影响。结果表明:1)随着金属铬加入量的增加,试样的体积密度、耐压强度及抗热震性能增加,当金属铬加入量(w)为3%时达到最大值。2)金属铬在高温下氧化生成Cr_(2)O_(3)产生体积膨胀,填充了试样中刚玉颗粒间的部分气孔,提高了试样的体积密度;生成的Cr_(2)O_(3)与Al_(2)O_(3)发生固溶反应形成铝铬固溶体,提高了基质与刚玉颗粒间的结合强度。3)加入金属铬还可以有效抑制熔渣向耐火材料内部的侵入,有效减少熔渣侵蚀深度。当加入量由0增加至3%(w)时,侵蚀深度由6.4 mm减小至4.1 mm。

无铬CO高温变换催化剂的研究 Ⅰ.氧化铬对高变催化剂结构与性能的影响

通过ＸＲＤ，ＢＥＴ和ＸＰＳ表征及反应活性测定表明，ＣＯ高温变换催化剂中加入的助剂ＣｒＯ３在制备及还原过程中，能进入Ｆｅ３Ｏ４晶格，使晶胞参数增大、晶粒度变小、分散度提高、比表面积和孔容积增大、孔结构改善而提高催化剂活性和稳定性．加入的ＣｒＯ３有７６％以Ｃｒ３＋形态存在于尖晶石的正八面体空隙中，２４％以Ｃｒ６＋形态存在于正八面体和正四面体空隙中．氧化铬不仅起到结构助剂作用，可能还起到电子助剂作用．加入的Ｃｒ２Ｏ３不进入Ｆｅ３Ｏ４晶格而以独立相存在，不起助剂作用．

CO_2气氛下负载型Cr_2O_3催化剂上乙苯脱氢制苯乙烯反应

采用浸渍法制备了负载型Cr2 O3 /Al2 O3 和Cr2 O3 /SiO2 催化剂 ,并考察了催化剂在CO2 气氛下催化乙苯脱氢制苯乙烯反应的活性 .结果表明 ,Cr2 O3 /Al2 O3 的催化活性高于Cr2 O3 /SiO2 .这可能是由于Cr2 O3 在Al2 O3 载体表面的分散度大大高于在SiO2 表面的分散度 .催化剂的催化活性与Cr2 O3 的负载量有关 ,在w(Cr2 O3) =2 5 %时 ,Cr2 O3 /Al2 O3 的催化活性最高 .CO2 气氛对乙苯脱氢反应有明显的促进作用 ;在CO2 气氛下 ,Cr6+

溶胶-凝胶法制备用于CO_2气氛下乙苯脱氢反应的高活性Cr_2O_3-SiO_2催化剂

The Cr2O3-SiO ? catalyst was prepared by a sol-gel method. It displays two times higher catalytic activity for the dehydrogenation of ethylbenzene in the presence of CO2 than the regular SiO2-supported chromia catalyst.The higher amount of Cr 6+ present in the former catalyst accounts for its superior catalytic performance in the dehydrogenation reaction.

CrO_x/SiO_2催化剂对C_(10+)芳烃加氢脱烷基反应的催化性能

采用等体积浸渍法制备了一系列不同组成的CrOx/SiO2催化剂样品,并用XRD,FTIR,UVVis,TPR和N2吸附等技术对催化剂样品进行了表征,考察了催化剂对C10+重芳烃加氢脱烷基反应的催化性能.结果表明,CrOx/SiO2催化剂对C10+重芳烃加氢脱烷基反应的催化性能与催化剂的表面结构有关,脱烷基活性主要来自载体表面的CrOx物种.当催化剂中n(Cr)/n(Si)=1%～2%时,CrOx在SiO2表面达到单层分散;当n(Cr)/n(Si)=2%～20%时,表面CrOx物种含量的变化不大,催化剂的活性及选择性基本不变.

纳米Cr_2O_3系列催化剂上CO_2氧化乙烷脱氢制乙烯反应

采用溶胶 凝胶法和共沸蒸馏法耦合技术制备了纳米Cr2 O3 催化剂 ,并采用共沉淀法和共沸蒸馏法耦合技术制备了纳米Cr2 O3 /Al2 O3 ,Cr2 O3 /ZrO2 和Cr2 O3 /MgO复合催化剂 .应用BET ,XRD ,XPS ,TPR和TEM等物理化学方法对催化剂的结构和物化性质进行了表征 ,并考察了该系列催化剂上CO2 氧化乙烷脱氢制乙烯的反应性能 .结果表明 ,纳米Cr2 O3 催化剂上乙烷和CO2 的转化率均明显高于常规Cr2 O3 催化剂 ,但乙烯的选择性低于常规Cr2 O3 催化剂 ;纳米复合催化剂中的复合成分显著影响催化剂的催化性能 .其中 ,10 %Cr2 O3 /MgO纳米复合催化剂在温度为 973K时 ,乙烷转化率和乙烯选择性分别可达到6 1 5 4 %和 94 79% .纳米催化剂表面Cr的还原性以及Cr6+/Cr3

Zn-Cr整体催化剂中Ce-Zr溶胶涂层的制备、表征及对甲醇自热重整反应的影响

以溶胶-凝胶法制备出粒子尺度均一的Ce-Zr溶胶. TEM和XRD结果表明, 1073 K焙烧后, Ce-Zr复合氧化物的粒径仍保持在20～50 nm. 将Ce-Zr溶胶作为甲醇自热重整制氢Zn-Cr整体催化剂的涂层,考察了溶胶在涂层多次重复过程中的稳定性和干燥方式对Ce-Zr涂层龟裂程度的影响. 结果表明,对多次使用后的溶胶进行胶溶处理可以有效控制涂层制备过程中胶体粒子的大小; 微波干燥更加有利于蜂窝陶瓷载体各通道中Ce-Zr涂层的均匀干燥; Ce-Zr涂层的引入显著提高了甲醇自热重整Zn-Cr整体催化剂的稳定性,这归因于Ce-Zr涂层提高了催化剂的氧化还原活性,使其能量匹配更好,避免了热点的产生,从而抑制了催化剂的烧结与失活.

氧化铬柱层状三氧化钼的合成

采用醋酸铬[Cr(OAc)_3]水溶液与具有层状结构的钼青铜{[Na(H_2O)_5]_(0.025)MoO_3}进行离子交换反应制得铬齐聚体柱撑的层状氧化钼化合物.经350℃焙烧后,首次得到了多孔高比表面积的氧化铬柱层状氧化钼材料.通过XRD,TEM,DTA和BET测试手段对其进行了表征,并考察了350℃时不同的焙烧气氛对产物层间距和表面积等的影响.结果表明,在不同气氛中焙烧,产物层间距相同(1.092nm),但比表面积有很大的变化,其中,在含4%(体积分数)氧气的氮氧混合气中焙烧,获得的样品比表面积(BET)最大,达 82.4m_2·g^(-1),平均孔径为6.42nm.

氧化铬柱支撑蒙脱石的制备研究

以浙江和新疆的膨润土为原料合成了氧化铝柱支撑蒙脱石，成柱溶液以Na2CO3为碱水解铝盐溶液制得。因为制备含有大聚羟基铬阳离子的成柱溶液是获得具有大的基面间距的柱支撑粘土的关键，我们详细研究了CO32-／Cr3＋值、水解温度和水解时间对所得柱支撑蒙脱石性质的影响。聚羟基铬阳离子通过阳离子交换引入蒙脱石，所得产物用X射线衍射分析和BET氮比表面等方法研究。所得氧化铝柱支撑蒙脱石（简称Cr－mont）的基面间距为2．55nm，BET氮比表面积为190～230m2／g。

磷酸盐添加剂对氧化铬材料性能的影响

为了提高氧化铬材料的物理性能和抗煤渣的渗透性能,延长其在水煤浆气化炉内的使用寿命,以氧化铬为主要原料,磷酸盐为结合剂,于1 780℃下烧成后,研究了磷酸盐加入量(分别占原料总质量的1%、2%、3%和4%)对烧后氧化铬材料体积密度、抗折强度、抗热震性以及抗熔渣侵蚀渗透性能的影响。结果表明:随着磷酸盐加入量的增加,试样的致密度呈升高趋势;添加3%磷酸盐试样的常温抗折强度和高温抗折强度最高,分别达到25.4 MPa和38.8 MPa(1 400℃下);随着磷酸盐加入量的增加,试样的抗热震性呈增加趋势;添加适量磷酸盐有利于提高氧化铬材料的抗熔渣渗透性能,当其加入量由1%增加到3%时,熔渣渗透深度由6 mm减小至2 mm,但磷酸盐加入量增加到4%时,熔渣渗透深度又增加至8 mm。

多弧离子镀Cr_2O_3涂层对γ-TiAl抗氧化性能的影响

用多弧离子镀技术在γ-TiAl金属间化合物表面制备了Cr2O3涂层,用SEM/EDX线扫描分析等手段研究了该涂层在900℃下的循环氧化行为.结果表明,γ-TiAl表面沉积Cr2O3涂层后,明显提高了γ-TiAl的抗循环氧化能力;在氧化过程中TiAl/Cr2O3界面处的低氧压促进了Al的选择性氧化,在TiAl一侧生成了一层富Al氧化物,该层富Al氧化物较好地阻止了TiAl中Ti的外扩散,从而抑制了TiO2的生长.

氧化铬层柱磷酸锆的制备及催化性能

详细研究了有机胺品种、层板预撑态、水解度以及Ｃｒ加入量等制备因素对氧化铬层柱磷酸锆结构和性能的影响．用乙胺胶体化法制备的氧化铬层柱磷酸锆比表面积可高达４８２ｍ２／ｇ，而孔径集中在２６ｎｍ附近．层板胶体化时表面磷酸根的适度水解有利于提高层柱产品的比表面积和形成规整的平板型层间孔．用ＴＧ，ＩＲ，ＸＲＤ和Ｎ２吸附等温线方法研究了氧化铬柱子的形成过程和热稳定性．异丙醇脱水和异丙苯裂解反应结果表明，氧化铬层柱磷酸锆表面含有中强酸位或中强和弱酸位并存．氧化铬层柱磷酸锆对环己烷和乙苯脱氢反应较负载型催化剂Ｃｒ２Ｏ３／ＳｉＯ２具有更高的催化活性．

氧化铬柱层状铌酸的合成和表征

本文报道先用正丙胺预支撑层状铌酸，然后同氯化四甲铵水溶液进行离子交换，最后再与醋酸铬（ Ⅲ） 水溶液反应可得含铬（ Ⅲ） 聚合离子支撑的层状铌酸。进一步焙烧所得含铬（ Ⅲ） 聚合离子支撑的层状铌酸可得氧化铬柱层状铌酸。该材料具有较高的热稳定性（ ＞ ７００ ℃） 和 Ｂ Ｅ Ｔ 比表面（６６ ．７ ｍ２／ｇ） ，是一类中等偏弱的新型多孔固体酸（ 平均孔径为３ ．３ ｎｍ ，总酸量为１８８ ．３ μｍｏｌ／ｇ ，且主要为 Ｌｅｗｉｓ 酸） 。