催化剂Pd/CeO_2中Pd与CeO_2之间的SMSI对汽车尾气的催化活性的影响

在汽车尾气模拟配气的条件下 ,用XRD和CO吸附技术研究了催化剂Pd/CeO2 中的Pd与CeO2 之间的SMSI对尾气的催化活性。结果发现高温还原能在催化剂Pd/CeO2 上形成SMSI ,并且这种强相互作用能够显著地提高催化剂对尾气的催化活性     

CeO2基氧化物在氧化羰基化合成碳酸二苯酯中的应用

用溶胶一凝胶法制备了系列CeO2基复合金属氧化物载体,用沉淀法负载活性组分Pd得到0．5％Pd固相催化剂,采用XRD、SEM、BET等手段对载体进行了表征。以非均相催化苯酚一步合成碳酸二苯酯的反应为考察对象,对催化活性进行了评价。结果表明,CeO2经金属元素掺杂后其催化活性可得到明显的提升,其中经锰掺杂催化活性最好,DPC收率可达9．33％。     

Pd/Al2O3催化剂的制备及其在对氨基苯酚合成中的应用

用等体积浸渍法制备了Pd/Al2O3催化剂。采用ICP、XRD、HRTEM和XPS等对催化剂的组成和形貌进行表征。结果表明，Pd粒子均匀分布在Al₂O₃的表面，粒径约为5 nm。在对硝基苯酚催化加氢制备对氨基苯酚的反应中，对催化剂的催化性能进行了考察。Pd/Al₂O₃催化剂的催化活性随着Pd负载量的增大而增大；其与市售的骨架镍、纳米镍以及2%Pd/C相比，显现了优异的催化活性；Pd/Al₂O₃具有高的催化选择性；Pd/Al2O3的催化活性稳定性明显优于骨架镍；随着使用次数的增加，Pd/Al₂O₃的催化活性有所降低，这可能是因为Pd粒子的团聚。     

Ag/CeO2-ZnO催化剂上甲醇部分氧化制氢气研究

研究了用于甲醇部分氧化制氢气反应的Ag/CeO2-ZnO催化剂的制备条件以及反应条件对催化剂性能的影响.Ag/CeO2-ZnO催化剂中银含量、焙烧温度、反应温度以及反应气的比例等对催化剂性能具有很大的影响.Ag/CeO2-ZnO催化剂的制备条件以及反应条件控制在一定范围内时,Ag/CeO2-ZnO催化剂对甲醇部分氧化制氢气具有很高的催化活性与选择性.     

纳米CeO2负载Pd催化木质素磺酸盐氢化活化研究

采用水热合成和甲醛还原法,以纳米CeO_2为载体,负载Pd制备催化剂。通过SEM、BET法对催化剂结构进行表征。利用环己烯在水热反应釜中氢化活化木质素。用化学滴定分析方法和紫外示差法检测木质素磺酸盐氢化反应前后总羟基和酚羟基含量,采用FTIR光谱对反应前后木质素磺酸盐化学结构进行了分析。结果表明,制备的Pd/CeO_2对木质素磺酸盐氢化还原反应具有较高的催化活性。     

生物还原法制备Pd/TiO2光催化剂

用芳樟叶煮液将PdCl2还原成Pd单质纳米颗粒,将其沉积于TiO2上制得Pd/TiO2催化剂,采用X射线衍射(XRD),扫描电镜(SEM)和能量色散谱仪(EDS)对催化剂进行表征,并以甲基橙为目标降解物评价Pd/TiO2催化剂的光催化降解活性.结果表明,Pd/TiO2催化剂中的Pd纳米颗粒的平均粒径小于10 nm,能够很好地分散在TiO2表面,且不改变TiO2锐钛矿的晶型结构.与未负载Pd的TiO2催化剂相比,Pd/TiO2光催化剂对甲基橙有更高的光催化降解活性,能够提高甲基橙的降解速率.在实验范围内.Pd与TiO2质量比为5%的催化剂活性最高,反应30 min甲基橙就能完全降解,而空白TiO2催化剂在反应1 h时降解率只达到95%.Pd与TiO2质量比为5%的Pd/TiO2光催化剂矿化率可达到96.2%,且重复使用仍能保持良好的催化活性.     

负载型CeO2/OMS -2催化剂对VOCs的催化氧化性能

采用回流法合成了OMS -2,同时以OMS -2为载体,采用浸渍法负载CeO2制备了Ce/OMS-2催化剂,运用X射线衍射、拉曼光谱、BET、H2 - TPR和NH3 - TPD等方法对催化剂进行表征,并考察CeO2/OMS -2催化剂催化氧化二氯甲烷和乙酸乙酯的性能.结果表明,CeO2的加入并未改变OMS -2较好的八面体分子筛结构,CeO2的晶粒很小且以高分散的形式存在;负载CeO2的OMS -2催化剂比表面积都有增大趋势;随着CeO2负载量的增加,低温和高温的还原峰都先向低温方向偏移再向高温方向偏移;随着CeO2负载量的增加,高温处强酸性峰先向低温方向偏移再向高温方向偏移.反应活性结果表明,CeO2/OMS -2催化剂活性比载体OMS -2的活性好,随着铈负载量的增加,催化活性先升高再降低,其中,CeO2负载质量分数为1.0％(1.0Ce/OMS -2)时催化剂效果最好,这可能是由于铈的加入活化了OMS -2中的氧,影响了整体催化剂的酸性,进而影响反应性能.     

CeO2-ZrO2对柴油机油烟氧化和钾催化剂热稳定性的影响

研究制备了硝酸钾负载于不同氧化物（CeO2、Ce0.5Zr0.5O2和ZrO2）上的催化剂用于柴油机油烟的燃烧。试验中，将制备好的催化剂在800℃老化处理24h，然后采用程序升温氧化工艺评价该催化剂的催化活性。     

Mo改性Pd/Al_2O_3催化剂的HC-SCR催化活性的研究

最近的研究表明,非贵金属的掺杂不仅可以通过改善贵金属Pd催化剂的织构、结构、氧化还原等性能来提高其HC-SCR的催化活性、选择性、稳定性,同时还可以降低贵金属用量从而降低催化剂成本,为其商业化应用做出贡献。基于提高Pd催化活性及降低其用量的目的,通过添加廉价的造孔剂对商业化Al_2O_3进行改性,制备出孔隙率高的Al_2O_3基底,然后通过浸渍法成功制备出Mo改性的Pd/Al_2O_3催化剂,并通过XRD,BET,NH_3-TPD,H_2-TPR,XPS对催化剂进行表征,系统研究了Mo掺杂对Pd催化剂的HC-SCR催化性能的影响,研究表明适当的Mo掺杂可以提高催化剂的催化活性,且当Mo掺杂为5%的时候催化效果最佳。     

自组装低负载量Pd/γ-Al2O3催化剂催化氧化甲苯

以PdCl_2和Pd2(dba)3[三(二亚苄基丙酮)二钯]为前驱体,通过浸渍法、沉积沉淀法和自组装法分别制备了负载量(质量分数,下同)为0.03%的Pd/γ-Al_2O_3-IM、Pd/γ-Al_2O_3-DP和Pd/γ-Al_2O_3-SA催化剂用于催化氧化甲苯。在甲苯体积分数为0.1%、空速(SV)为18000 m L/(g·h)条件下,Pd/γ-Al_2O_3-SA催化剂上甲苯实现98%转化率的温度(T98)为220℃,比Pd/γ-Al_2O_3-DP和Pd/γ-Al_2O_3-IM分别降低了40和75℃。通过N2吸附-脱附、XRD、TEM、XPS和H2-TPR对催化剂进行了表征。结果表明:自组装法制备的Pd/γ-Al_2O_3-SA催化剂的比表面积(345 m2/g)和孔体积(0.52 cm3/g)最大,Pd纳米粒子(Pd NPs)平均粒径最小(5.0 nm),活性物种主要以Pd O的形式高度分散于载体γ-Al_2O_3表面。此外,Pd O与载体γ-Al_2O_3之间的强相互作用(SMSI)促进了其催化氧化甲苯的活性。     

Selective hydrogenation of acetylene over Pd/CeO2

Five hundred ppm Pd/CeO₂ catalyst was prepared and evaluated in selective hydrogenation of acetylene in large excess of ethylene since ceria has been recently found to be a reasonable stand-alone catalyst for this reaction. Pd/CeO₂ catalyst could be activated in situ by the feed gas during reactions and the catalyst without reduction showed much better ethylene selectivity than the reduced one in the high temperature range due to the formation of oxygen vacancies by reduction. Excellent ethylene selectivity of ~100% was obtained in the whole reaction temperature range of 50°C–200°C for samples calcined at temperatures of 600°C and 800°C. This could be ascribed to the formation of Pd_xCe_1−xO_2−y or Pd-O-Ce surface species based on the X-ray diffraction and X-ray photoelectron spectroscopy results, indicating the strong interaction between palladium and ceria.     

Partial oxidation of ethanol over Pd/CeO2 and Pd/Y2O3 catalysts

The effect of the support nature on the performance of Pd catalysts during partial oxidation of ethanol was studied. H₂, CO₂ and acetaldehyde formation was favored on Pd/CeO₂, whereas CO production was facilitated over Pd/Y₂O₃ catalyst. According to the reaction mechanism, determined by DRIFTS analyses, some reaction pathways are favored depending on the support nature, which can explain the differences observed on products distribution. On Pd/Y₂O₃ catalyst, the production of acetate species was promoted, which explain the higher CO formation, since acetate species can be decomposed to CH₄ and CO at high temperatures. On Pd/CeO₂ catalyst, the acetaldehyde preferentially desorbs and/or decomposes to H₂, CH₄ and CO. The CO formed is further oxidized to CO₂, which seems to be promoted on Pd/CeO₂ catalyst.     

CO oxidation on Pd/CeO2–ZrO2 catalysts

The promotive effects of cerium oxide on commercial three-way catalysts (TWCs) for purification of motor exhaust gases have been widely investigated in recent years. This work shows the cooperative effects of CeO₂–Pd on the kinetics of CO oxidation over Pd/CeO₂–ZrO₂. Under reducing-to-moderately oxidizing conditions, a zero-order O₂ pressure dependence is found which can be interpreted on the basis of a mechanism involving a reaction between CO adsorbed on Pd and surface oxygen from the support. The high oxygen-exchange capability of the CeO₂–ZrO₂ support, as determined from temperature-programmed reduction/oxygen uptake measurements is suggested as being responsible for such a catalytic behavior.     

Methane combustion over Pd/ZrO2/SiC,Pd/CeO2/SiC,and Pd/Zr0.5Ce0.5O2/SiC catalysts

The performances of different promoters (CeO₂, ZrO₂ and Ce_0.5Zr_0.5O₂ solid solution) modified Pd/SiC catalysts for methane combustion are studied. XRD and XPS results showed that Zr⁴⁺ could be incorporated into the CeO₂ lattice to form Zr_0.5Ce_0.5O₂ solid solution. The catalytic activities of Pd/CeO₂/SiC and Pd/ZrO₂/SiC are lower than that of Pd/Zr_0.5Ce_0.5O₂/SiC. The Pd/Zr_0.5Ce_0.5O₂/SiC catalyst can ignite the reaction at 240 °C and obtain a methane conversion of 100% at 340 °C, and keep 100% methane conversion after 10 reaction cycles. These results indicate that active metallic nanoparticles are well stabilized on the SiC surface while the promoters serve as oxygen reservoir and retain good redox properties.     

Complete oxidation of methane on Pd/YSZ and Pd/CeO2/YSZ by electrochemical promotion

In this work, methane combustion over Pd/YSZ and Pd/CeO₂/YSZ catalyst was investigated at a temperature range of 470–600 °C. For the first time, the feasibility of electrochemical promotion on palladium films prepared by wet impregnation was reported. The catalytic activity of palladium was found to increase over 160% via transference of oxygen ions from the solid electrolyte to the catalyst film. In addition, palladium supported over ceria and yttria-stabilized zirconia showed the highest activity. As expected, the presence of ceria allowed improving the oxygen storage capacity of the catalyst system.     

CO oxidation at low temperature over Pd supported on CeO2-TiO2 composite oxide

Low temperature CO oxidation was carried out over CeO₂-TiO₂ composite oxide and thereon supported Pd catalysts. The effects of Ce/Ti ratio and pre-treatments of calcination and reduction on the catalytic behaviour were investigated. The CO oxidation starts at about 220 °C over CeO₂-TiO₂ and the pre-reduction treatment has little influence on the catalytic activity. Pd supported on CeO₂-TiO₂ (Pd/CeO₂-TiO₂) exhibits high activity for CO oxidation and a complete conversion of CO to CO₂ can be achieved even at ambient temperature, which suggests a synergistic effect between Pd and CeO₂-TiO₂. The activity and stability of Pd/CeO₂-TiO₂ can be further improved by the pre-reduction treatment. Ce/Ti ratio influences the catalytic behaviour significantly; the catalyst Pd/CeO₂-TiO₂ with a Ce/Ti mole ratio of 0.20 (Pd/Ce20Ti) owns the highest activity and stability, which suggests an optimization of the Pd-Ce-Ti interaction in Pd/Ce20Ti. The calcined Pd/CeO₂-TiO₂ with a Ce/Ti mole ratio higher than 0.10 shows a distorted light-off profile with the temperature, which implies an alternation of the reaction mechanism with increasing temperature.     

Non-steady activity during methane combustion over Pd/Al2O3 and the influences of Pt and CeO2 additives

Methane combustion over Pd/Al₂O₃ catalysts with and without added Pt and CeO₂ in both oxygen-rich and methane-rich mixtures at temperatures in the range 250–520°C has been investigated using a temperature-programmed reaction procedure with on-line gas analysis (FTIR). During the temperature loop under oxygen-rich conditions, there was an appreciable hysteresis in the activity of unmodified Pd/Al₂O₃, which was greatly enhanced over Pd–Pt/Al₂O₃. Over both catalysts the hysteresis was reversed under slightly methane-rich atmospheres, and as temperature was reduced, a sudden collapse or fluctuations in activity were shown respectively over Pd–Pt/Al₂O₃ and Pd/Al₂O₃. Such non-steady behaviour was almost eliminated over Pd/Al₂O₃–CeO₂. Under a very narrow range of conditions and over a Pd/Al₂O₃ packed bed, oscillation of methane combustion was observed.     

Microporous high-surface area layered CeO2

A simple procedure for the obtaining of microporous high-surface area layered ceria is described. The synthesis consists of the formation of cerium hydroxide by precipitation of cerium (III) chloride with ammonium carbonate followed by a calcination step. The samples obtained were calcined at temperatures from 150 °C to 350 °C. The effects of calcination temperature on the crystalline phase, particle size, anisotropy, surface area and the textural, morphological and reducibility properties have been studied by powder X-ray diffraction, BET, scanning electron microscopy and temperature-programmed reduction techniques. The anisotropic effects on the particle growth were studied by means of a Williamson–Hall plot.     

Microstructure of Pd/CeO2 catalyst: Effect of high temperature reduction in hydrogen

The effect of high temperature reduction (HTR) in hydrogen (up to 1180 K) on the microstructure of 9 wt.-% Pd/CeO₂ catalyst was studied by HRTEM and XRD methods. Reduction of the catalyst at or above 973 K caused severe recrystallization of CeO₂ and Pd with simultaneous strong interaction between the two components appearing as three phenomena: epitaxial growth of small Pd particles on CeO₂ (most frequently with [111]Pd[111]CeO₂); decoration of large Pd particles with ordered CeO₂ overlayer and expansion of the lattice parameter of Pd (by 2.1%). The origin of the Pd lattice expansion is discussed and diffusion of Ce species into the Pd lattice seems to be the most probable one. HTR caused also phase transformations in the ceria support. At 973 K and 1100 K, whole CeO₂ was transformed into oxygen deficient CeO_x phase exhibiting the same or similar structure but with expanded lattice parameter (by 2.8%). At 1180 K most ceria was transformed into hexagonal A-Ce₂₃. The CeO_x phase appeared to be stable in hydrogen and in vacuum at room temperature, but upon exposure to air at room temperature it rapidly reoxidised to CeO₂. Ce₂O₃ also reoxidised to CeO₂ but much slower. Another consequence of HTR at or above 773 K was formation of pits in CeO₂ crystallites, mainly on (112)-type crystal faces. The pits (1–10 nm) exhibited well defined walls parallel to CeO₂ lattice fringes and they could possibly constitute nucleation sites for strongly bonded, epitaxial oriented Pd particles.     

Synthesis and electrochemiluminescence of the CeO2/TiO2 composite

CeO₂/TiO₂ composite with kernel–shell structure was synthesized by a sol–gel process. The characterization results show that the composite is made up of anatase phase TiO₂ and cubic system CeO₂. The electrochemiluminescence (ECL) behavior of the CeO₂/TiO₂ composite was studied by a cyclic voltammetry in the presence of persulfate, and the effect factors on ECL emission were discussed. Based on a series of experiments, it is proposed that the strong dual ECL emission produced by the CeO₂/TiO₂ composite resulted from the benefit ECL effect of interface heterojunction in composite.