Complete Oxidation of Methane over Palladium Supported on Alumina Modified with Calcium,Lanthanum,and Cerium Ions

The activity and thermal stability of Pd/Al_2O_3 and Pd/(Al_2O_3 MO_x)(M=Ca,La,Ce) palladium catalysts in the reaction of complete oxidation of methane are presented in this study.The catalyst supports were prepared by sol-gel method and they were dried either conventionally or with supercritical carbon dioxide.Then they were impregnated with palladium nitrate solution.The catalysts with unmodified alumina had a high surface area.The activity and thermal stability of the alumina- supported catalyst was also very high.The introduction of calcium,lanthanum,or cerium oxide into alumina support caused a decrease of the surface area in the way dependent on the support precursor drying method.These modifiers decreased the activity of palladium catalysts,and they required higher temperatures for the complete oxidation of methane than unmodified Pd/Al_2O_3.The improvement of the palladium activity by lanthanum and cerium support modifier was observed only at low temperatures of the reaction.     

介孔Al2O3负载PdO催化甲烷燃烧反应性能

采用浸渍法制备了介孔Al2O3(M-Al2O3)负载PdO催化剂,考察了其催化CH4燃烧反应性能.结果表明,以M-Al2O3为载体的PdO催化剂活性比普通Al2O3载体高得多,这很可能与M-Al2O3的孔道结构对PdO物种的限域作用有关.随着PdO/M-Al2O3催化剂焙烧温度的升高,甲烷催化燃烧活性先增加后降低,其中700oC焙烧的催化剂活性最高,400oC反应时CH4转化率为91%.此时Pd物种主要以PdO颗粒形式高度分散在载体的介孔孔道内,而高温焙烧时,Pd物种主要以Pd和PdO的混合晶相存在.尽管900oC焙烧制得的催化剂上CH4的转化率降低,但TOF值最大,这可能与该催化剂中同时存在金属Pd和PdO有关.     

镧和铈改性对氧化铝性质的影响

 以拟薄水铝石为前驱物，采用溶胶法制备了γ－Al2O3，在制备 初期添加硝酸镧或硝酸铈对氧化铝进行改性，并使用红外光谱、氮物理 吸附和X射线衍射等方法对样品进行了表征．实验表明，稀土添加物覆 盖了部分氧化铝的表面羟基．在1000℃下对样品烧结行为的考察发现， 添加镧或铈化合物都能提高γ－Al2O3的抗烧结性能和高温稳定性，镧 改性样品的效果略优于铈改性样品．烧结动力学研究发现，制备的氧化 铝的烧结机理为体相扩散，加入稀土有效地阻止了氧化铝颗粒内的体相 扩散．用微反装置测定了改性样品的反应性能，发现铈改性样品有一定 的裂化性能和脱氢性能，而镧改性样品几乎无催化活性．     

负载型CeO2-ZrO2固溶体的性能及其在甲烷燃烧Pd催化剂中的应用

以硅改性的氧化铝为载体,用反相微乳液法合成了负载型的CeO2-ZrO2固溶体(Ce-Zr-O/Si-Al2O3),用低温氮吸附、X射线衍射、程序升温还原、拉曼光谱和x射线光电子能谱等方法对Ce-Zr-O/Si-Al2O3的织构性能、热稳定性和储放氧性能等进行了表征.结果表明,负载后的CeO2-ZrO2晶相与负载前相比没有变化,但热稳定性和在低温下的放氧能力及总储氧量明显提高.作为甲烷燃烧Pd催化剂的载体,Ce-Zr-O/Si-Al2O3的性能明显优于CeO2-ZrO2,Si-Al2O3和机械混合物CeO2-ZrO2 Si-Al2O3.使用0.2%Pd/10?-Zr-O/Si-Al2O3为催化剂时,甲烷90%转化率时的温度仅为345℃,比负载在其它载体上的Pd催化剂低175℃.     

Catalytic Methane Oxidation Over Pd Supported on Nanocrystalline and Polycrystalline TiO2 Mn3O4, CeO2 and ZrO2

The catalytic oxidation of methane has been examined over Pd supported on nanocrystalline (n-) and polycrystalline (p-) TiO₂, Mn₃O₄, CeO₂ and ZrO₂. In all cases the Pd supported on the nanocrystalline oxides performs better on a mass basis than Pd supported on the polycrystalline oxides. Conversion vs temperature curves indicate that n-ZrO₂ is more active than p-ZrO₂ and that calcining both n-ZrO₂ and p-ZrO₂ at 500°C produces better catalysts than calcining at 280°C. n-CeO₂ is a very good catalysts for methane oxidation, while p-CeO₂ is not, and Pd supported on n-CeO₂ performs much better than bare n-CeO₂ and somewhat better than Pd supported on p-CeO₂; Pd supported on n-Mn₃O₄ or p-Mn₃O₄ does not perform as well as CeO₂-supported Pd catalysts. The 5 wt.% Pd/n-ZrO₂ catalyst calcined at 500°C performs very well, achieving 100% conversion at 320°C for the reactor conditions used, while 5 wt.% Pd/n-CeO₂ exhibits initial activity at the lowest temperature of about 100°C. The best catalyst tested in this study is 30 wt.% Pd/n-TiO₂, which achieves 100% conversion at 300°C.     

氧化铈对Pd催化剂氧化活性和热稳定性的影响

氧化铈对Pd催化剂氧化活性和热稳定性的影响;钯催化剂;催化氧化     

Pd／硫酸化氧化铝一种新型甲烷选择还原NO催化剂

 中译文： 最近，以甲烷为还原剂选择性还原NO引起人们的极大关注[ ，2]. 已有的结果表明：钯基催化剂对该反应有较高的活性[3-6]. 然而，在该反应中，钯基催化剂的活性对载体的性质有很强的依赖性[3，4]. 迄今为止，只有酸性的沸石[3，4]和酸性的氧化锆[4-6]被证明是钯基选择性还原NO催化剂的有效载体. 相反，Pd/g-Al2O3作为目前最被广泛应用的一种三效催化剂[7]，对于甲烷选择性还原NO反应只有很低的活性[3]. 在本工作中，我们首次研究了一系列担载Pd的硫酸化氧化铝（SA）催化剂上甲烷选择性还原NO反应并考察了Pd含量对催化剂活性的影响。 硫酸化氧化铝（SA）按照Hamada等人[8]的方法, 将g-Al2O3（分析纯，上海试剂公司，中国）用2.5 mol/L硫酸溶液按照15 ml/g 比例浸渍, 得到产物缓慢搅拌半小时, 然后不洗涤直接过滤并在110 ℃下干燥过夜. 通过用氯化钯的水溶液等体积浸渍的方法实现Pd的担载. 所有样品先在110 ℃下干燥8小时，然后在600℃下空气氛中焙烧6小时. 反应在固定床反应器中进行，混合气 (组成为：0.2 % NO, 0.2 % CH4, 2.0 % O2, He为底气) 以60毫升/分钟的流速流过1毫升催化剂（GHSV=3600 h-1）. 气体产物用气相色谱在线分析. NO转化率以N2的产率计算，甲烷的转化率由其消耗量来计算. 图1给出了四种不同催化剂上NO和CH4转化率与反应温度的关系. 由图1可见，g-Al2O3对甲烷选择性还原NO只有微弱活性. 硫酸化后，NO和CH4的转化率都明显下降. 这种活性下降可以归因为硫酸化后在g-Al2O3表面上生成了活性更低的硫酸铝的缘故[8]. 当我们将0.1 wt.% Pd担载到g-Al2O3 和 SA上时，两种载体的催化活性发生了明显的变化. 与Misono等人[3]一样，我们发现担载 0.1 wt.% Pd后，g-Al2O3上甲烷转化率增加，但NO的转化率仍然很低. 这一结果表明，在g-Al2O3上担载Pd后，只促进了燃烧反应. 另一方面，担载Pd后，SA上的NO和CH4转化率都明显提高. 在Pd/SA上，NO转化率于500℃达到最大值75 %. 显而易见，SA是一种用于甲烷选择性还原NO反应的Pd催化剂的新型载体，载体的硫酸化对提高甲烷还原NO的选择性是必要的. SA可以通过硫酸溶液浸渍商业化的g-Al2O3获得，这就使其比酸性的沸石或酸性的氧化锆更便宜和更容易获得. 因此我们认为SA有希望成为一种用于甲烷选择性还原NO的Pd催化剂的商业化载体. Pd含量对Pd/SA催化剂催化活性的影响如图2所示. 可以看出Pd/SA催化剂的活性随Pd含量的增加而增加，当Pd的含量为0.1 wt.%左右时达到最大值，然后下降. 这一结果表明对于Pd/SA催化剂，Pd的最佳含量大约为0.1 wt.%.     

氯离子及水蒸气对Pd／Al2O3催化剂甲烷燃烧性能的影响

考察了残余Cl-及水的添加对负载型Pd/Al2O3催化剂甲烷燃烧性能的影响.结果表明,含Cl-的催化剂活性较低,水的加入可使催化剂迅速失活,在高温下通过N2吹扫可使催化剂再生.采用N2吸附、X射线荧光分析、红外光谱和热重分析对催化剂进行了表征.结果表明,Cl-的存在会降低Pd在载体上的分散度,且对Pd/Al2O3催化剂的活性有强烈的抑制作用;添加的水会覆盖催化剂活性位并与PdO生成催化活性较低的Pd(OH)2,从而使得催化剂活性下降。     

Methane Combustion over Pd/Al2O3 Catalyst: Effects of Chlorine Ions and Water on Catalytic Activity

The influences of residual chlorine ions and water on the performance of a Pd/Al₂O₃ catalyst in methane combustion have been studied. The results show that the catalyst containing Cl⁻ exhibits a relatively low activity, and the addition of water to the reaction system accelerates the deactivation process. The catalyst has been characterized by N₂ adsorption, X-ray fluorescence, Fourier transform infrared spectroscopy (FT-IR), and thermogravimetry (TG). The results show that the presence of Cl⁻ appears to strongly inhibit the total oxidation of methane and hinder the dispersion of Pd on Al₂O₃. The formation of Pd(OH)₂ during the reaction is the most likely reason for the inhibition effect of water, which is confirmed by FT-IR and TG analysis. The regeneration of the Pd/Al₂O₃ catalyst can be achieved by purging in nitrogen at 550 °C.     

The Role of Vanadia for the Selective Oxidation of Benzyl Alcohol over Heteropolymolybdate Supported on Alumina

A series of 12-molybdophosphoric acid (MPA) supported on V2O5 dispersed γ-Al2O3 catalysts with different vanadia loadings were prepared by impregnation and characterized by N2 adsorption-desorption,X-ray diffraction,temperature-programmed reduction,in situ laser Raman spectroscopy,UV-Vis diffused reflectance spectroscopy,scanning electron microscopy,and temperature-programmed desorption of NH3 techniques.Their catalytic activities were evaluated for the vapor phase aerobic oxidation of benzyl alcohol.The catalysts exhibited high catalytic activity and the conversion of benzyl alcohol depended on the vanadia content while the catalyst with 15 wt％ V2O5 content showed optimum activity.The characterization results suggest the presence of well-dispersed V2O5 and partially disintegrated Keggin ions of MPA on the support.In situ Raman studies showed a reduced Mo(IV) species when the catalysts were calcined at high temperatures.The high oxidation activity of the catalysts is related to the synergistic effect between MPA and V2O5.     

Effect of CeO2 and CaO Promoters on Ignition Performance for Partial Oxidation of Methane over Ni/MgO-Al2O3 Catalyst

The effect of CeO2 and CaO promoters on the ignition performance over Ni/MgO-Al2O3 catalyst for the partial oxidation of methane （POM） to synthesis gas was investigated. It was found that the POM reaction could not be ignited over lwt%Ni/MgO-Al2O3 catalyst without the promoters in the temperature range from 773 K to 1073 K. CeO2 and CaO promoters enhanced the ignition performance and the POM reactivity of lwt%Ni/MgO-Al2O3 catalyst remarkably. Moreover, the improving effect became greater with the increase of the promoter content under the investigated reactiorrconditions. The modification effects of CeO2 and CaO promoters were closely related to the concentration and reducibility of the surface and bulk oxygen species.     

铈铁复合氧化物制备及其甲烷选择性氧化制合成气催化性能

用共沉淀法制备了CeO2-Fe2O3氧载体。在固定床反应器中研究了氧载体中晶格氧部分氧化甲烷的反应,并用空气为氧源进行了氧载体还原-氧化再生循环实验,通过XRD,O2-TPD,H2-TPR等手段对氧载体进行了表征。结果表明,CeO2-Fe2O3氧载体中的体相晶格氧适于部分氧化甲烷制合成气。新鲜的氧载体上存在二种氧：有强氧化性的吸附氧（包括弱吸附分子氧和表面晶格氧）和高选择性的体相晶格氧。在高温条件下（800℃）,CeO2-Fe2O3氧载体在消耗掉吸附氧后能均匀地释放出体相晶格氧将甲烷高选择性的氧化为CO和H2。循环实验表明,可以通过循环来提高合成气的选择性,经长时间的循环CeO2-Fe2O3氧载体上有CeFeO3出现,但其并未对选择性造成不利影响。     

Deep Oxidation of Methane over Nano-Sized Ferrites with Spinel Structures

Ferrites with spinel structures as catalysts for the deep oxidation of methane have been studied by X-ray phase analysis and temperature programmed reduction. The most active catalysts are the nano-sized ferrites of cobalt and nickel, prepared by the decomposition of polynuclear complexes, with Al₂O₃ as carrier and with addition of a surface active agent to increase the thermal stability of the catalysts. At low temperatures (up to 450 °C), the effect of the size factor appears with the increase in specific catalytic activity of cobalt and nickel ferrites with decreasing of their particles. A correlation of the catalytic activity with the quantity and mobility (reactivity) of oxygen in the ferrites has been established.     

Ag对Pd/CeO2-ZrO2-La2O3-Al2O3催化氧化甲醇性能的影响

采用等体积共浸渍法制备了一系列Pd-Ag/CeO2-ZrO2-La2O3-Al2O3催化剂。运用N2吸附-脱附,X射线衍射(XRD),H2程序升温还原(H2-TPR),紫外-可见漫反射光谱(UV-Vis DRS),X射线光电子能谱(XPS)对催化剂进行表征,并考察其对甲醇的催化氧化性能。活性测试结果表明,Ag的添加可显著改善Pd催化剂对甲醇的催化氧化活性,T50、T90以及ΔT分别为125℃,150℃和25℃,具有较好的应用前景。H2-TPR表明,引入Ag可明显改善催化剂的还原性能,使表面易还原氧物种量增多,还原速率加快;UV-Vis DRS及XPS表明,Pd、Ag金属之间以及金属与载体之间存在电子效应,这种效应促使金属与载体界面产生大量具有活性的氧物种,不仅提高了催化剂的低温活性,还提高了催化剂的氧化速率。     

Effect of Ni Loading and Reaction Conditions on Partial Oxidation of Methane to Syngas

The partial oxidation of methane to synthesis gas is studied in this paper over Ni/Al2O3 catalysts under atmospheric pressure. The effects of Ni loading on the activity and stability of catalysts with 5 mm α-Al2O3 and θ-Al2O3 pellets as supports were measured in a continuous fixed bed reactor. It is found that the optimum Ni loading is 10%. And the effect of reaction conditions on partial oxidation of methane is also studied. The methane conversion and CO selectivity increase with the increase of the reaction temperature and the space velocity on 10%Ni/α-Al2O3 catalysts. The best CH4/O2 mole ratio is 2 for CO selectivity, and the optimum space velocity is 5.4x105 h-1.     

改性介孔 Al2O3 负载锰基催化剂的结构及其催化氧化与抗硫性能

 采用分步浸渍法分别制备了 LaCeZr 和 YCeZr 组合助剂改性的介孔 Al2O3 负载的 Mn 基系列氧化物催化剂, 用 X 射线衍射、氮气吸附-脱附、X 射线吸收精细结构、X 射线光电子能谱和程序升温还原等方法对催化剂进行了表征, 探讨了催化剂中 Mn 物种的存在形式及其还原性能, 并与样品催化 CO 和 C3H8 的氧化活性相关联. 结果表明, 样品中 Mn 物种主要以 Mn3O4 形式存在, 该物种在不同样品中与载体的作用强弱不同, 从而表现出不同的还原性能和催化活性. 助剂改性有效抑制了 Mn-Al 之间的相互作用, 提高了 Mn–O 键的活动度, 从而提高了催化剂的氧化活性. 相比于 YCeZr 助剂, LaCeZr 助剂改性更大程度上提高了 Mn 物种的还原性, 因而大大提高了催化剂的氧化性能. 650 oC 焙烧的 LaCeZr 组合助剂改性的介孔 Al2O3 负载的 Mn 氧化物催化剂, 在 0.035% SO2 存在的条件下对 CO 的氧化活性并未下降, 对 C3H8 的氧化活性下降幅度也较小, 表现出优越的抗硫性能和氧化性能.     

Partial Oxidation of Butane to Syngas over Nickel Supported Catalysts Modified by Alkali Metal Oxide and Rare-Earth Metal Oxide

There are abundant supplies of mixture gases containing CH4, C2H6, C3H8 and C4H10, etc. from FCC (Fluidized Catalytic Cracking) tail gas, refinery gas, etc. Commonly, the mixture gases are primarily combusted to carbon dioxide because the complete separation of CH4, C2H6, C3H8 and C4H10, respectively, from the mixture gases may not be economical. Provided that syngas (CO+H2) could be produced from the mixture gases over nickel supported catalysts with high selectivity and conversion,…     

Ni与Al2O3相互作用对Ni/Al2O3催化甲烷部分氧化制合成气抗积炭性能的影响

Ni/Al2O3是甲烷部分氧化制合成气反应常用的催化剂. 与Rh,Ru,Pt和Ir等贵金属负载型催化剂相比,其活性及选择性与Rh催化剂相近,且成本低,强度高,易于制备,是最具潜在应用前景的催化剂. 但是,在高温反应条件下,其活性组分Ni易烧结和流失,且催化剂表面易积炭而失活[1～3]. 此外,Ni与载体Al2O3在高温下相互作用生成难还原的NiAl2O4尖晶石,导致活性组分减少,造成催化剂活性下降. 人们通常都只注意到NiAl2O4的惰性,为了避免NiAl2O4晶相的生成,在消弱Ni与Al2O3之间的相互作用,提高催化剂的活性和稳定性等方面做了大量研究[4～7],但有关Ni与Al2O3之间的相互作用对稳定金属Ni的作用方面的报道却较少. Al-Ubaid等[8]发现Ni负载在NiAl2O4上显示出比其它载体更好的稳定性. Pena等[9]发现,NiAl2O4在乙炔加氢反应中有抑制积炭的作用. 范文浩等[10]在甲烷-二氧化碳重整制合成气催化剂的研究中,发现NiAl2O4的形成使催化剂的抗积炭性能大为改善,增强Ni-Al2O3相互作用,能有效地抑制碳丝生长. 本文在固定床流动反应装置上考察了Ni/Al2O3在甲烷部分氧化制合成气过程中的催化性能,并用XRD,XPS和TPR等手段考察了Ni负载量、焙烧温度和还原条件等对催化剂中Ni与Al2O3之间的相互作用及其对抗积炭性能的影响.     

Investigation on the Performance of Supported Molybdenum Carbide for the Partial Oxidation of Methane

The performance of uspported and unsupported molybdenum carbide for the partial oxidation of methane (POM) to syngas was investgated.An evaluation of the catalysts indicates that bulk molybdenum carbied has a higher methane conversion during the initial stage but a lower selectivity to CO and H2/CO ratio in the products.The rapid deactivation of the catalyst is also a significant problem.However,the supported molybdenum carbide catalyst shows a much higher methane conversion,increased selectivity and significantly improved catalytic stability.The characterization by XRD and BET specific area measurements depict an improved dispersion of molybdenum carbide when using alumina as a carrier.The bulk or the supported molybdenum carbide exists in the β-Mo2C phase,while it is transformed into molybdenum dioxide postcatalysis which is an improtant cause of molybdenum carbide deactivation.