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1.
Pd/NaZSM-5负载型催化剂上CO完全氧化研究   总被引:7,自引:2,他引:5  
毕玉水  刘建福  吕功煊 《化学学报》2002,60(9):1624-1629
采用浸渍法制备了一系列Pd/NaZSM-5负载型催化剂。考察了焙烧温度、反应温 度、Pd含量及预还原等对CO氧化性能的影响。结果表明:制备条件和反应条件对催 化活性均有较大影响,催化剂的活性随着焙烧温度的增加而降低,随反应温度及 Pd含量的增加而增加。XRD,TEM结果表明催化剂中Pd组分处于高分散状状;表面 XPS分析证实催化剂表面Pd物种PdO_2和PdO在反应过程中发生明显的表面化学变化 ,高价Pd物种随反应的进行逐步被CO还原为低价Pd物种,催化剂活性下降与Pd物种 被还原有关。H_2预还原作用也导致催化剂活性有所下降。  相似文献   

2.
通过简便的方法制备了炭负载Pd/Ce双金属催化剂,利用Pd/Ce双金属催化剂的协同效应提高催化剂对Heck反应的催化效率。 以碘苯与丙烯酸的Heck芳基化反应为模型反应,研究了反应条件对催化剂催化性能的影响。 结果显示,在反应温度为130 ℃,反应时间为5 h,N,N-二甲基甲酰胺(DMF)作为溶剂和三丁胺(Bu3N)作为碱的条件下,炭负载Pd/Ce双金属催化剂对丙烯酸和碘苯的Heck芳基化反应具有良好的催化性能,产率达到70%以上。 另外,该催化剂属于非均相催化剂,催化剂易与反应溶液分离;也可以重复利用,使用3次反应产率仍达到66.9%,显示了炭负载Pd/Ce双金属催化剂良好的催化活性。  相似文献   

3.
以三嵌段高聚物F-127为模板剂采用水热法合成了介孔ZnO(m—ZnO),以甲醇水蒸气重整制氢为探针反应,在连续流动反应条件下考察了Pd/m.ZnO催化剂的性能,并利用XRD、FT—IR、H2-TPR、TEM和BET等手段对载体及催化剂进行了表征.结果表明,该法所制m-ZnO具有较大的比表面积(124.7m^2/g),其比表面积不但高于非介孔ZnO,而且大于文献值(103.6m^2/g).与Pd/ZnO催化剂相比,Pd/m—ZnO催化剂中活性组份Pd的分散度较高以及与m—ZnO间的相互作用较强,因此该催化剂对甲醇水蒸气重整制氢反应具有较高的催化活性、氢气产率、CO2选择性和稳定性.250℃时,Pd/m—ZnO催化剂的催化活性、氢气产率和C02选择性分别比Pd/ZnO催化剂提高了38.4%、44.4%和30.0%,170oC连续反应100h后,Pd/m-ZnO催化剂的活性仍为95%,仅下降了4.9%.  相似文献   

4.
采用共沸精镏辅助的原位法成功合成了高度分散的Pd纳米颗粒负载在ZSM-5中(Pd/ZSM-5-IS)分子筛催化剂。通过XRD、TEM、XPS等手段对Pd/ZSM-5-IS的样品进行了表征,并考察反应压力、反应温度、反应时间对肉桂醛加氢催化性能的影响。结果表明:原位法制备的Pd/ZSM-5-IS催化剂比浸渍法制备的Pd/ZSM-5-IM催化剂具有更高的催化稳定性,其主要归因于Pd纳米颗粒进入ZSM-5的晶内介孔有效防止活性位点的损失和聚集。当反应温度为80℃,反应压力为1 MPa,反应时间为3 h时为最佳反应条件,肉桂醛的转化率为87.23%,苯丙醛的选择性为76.68%。  相似文献   

5.
通过等体积浸渍法制备了金属有机骨架材料MIL-53(Al) (MIL:Materials of Institut Lavoisier)负载纳米Pd催化剂. 采用X射线衍射(XRD)、透射电子显微镜(TEM)和X射线光电子能谱(XPS)等手段对催化剂的结构进行了表征. 催化剂在反应前后XRD衍射峰保持不变,说明载体MIL-53(Al)具有良好的稳定性. 采用TEM对催化剂进行表征,结果表明,MIL-53(Al)的多孔晶体结构有助于形成高度分散的纳米Pd颗粒,样品2.7% (w) Pd/MIL-53 中Pd颗粒的平均粒径为2.21 nm. 该催化剂在CO氧化反应中表现出较高的催化活性,115 ℃达到完全转化. 同时催化剂可循环使用,多次反应后催化活性和催化剂结构都保持稳定.  相似文献   

6.
单层分散型Pd/Ni双金属催化剂的制备及其催化加氢性能   总被引:1,自引:0,他引:1  
通过置换反应制备了Pd/Ni双金属催化剂,利用X射线衍射、CO化学吸附和吸附H2的程序升温脱附对其进行了表征,并测定了该催化剂对环己烯、苯乙烯和丙酮气相加氢反应的催化性能.结果发现,在这种催化剂中Pd原子单层分散在金属Ni的表面,因而该催化剂表现出比浸渍法制备的相同Pd含量的Pd/Ni-im和Pd/-γAl2O3催化剂更高的催化加氢活性.  相似文献   

7.
徐庶亮  楚文玲  杨维慎 《催化学报》2010,31(11):1342-1346
 采用不同负载顺序或制备过程制备了 Pd-SiW12/SiO2 催化剂, 考察了它们在乙烯直接氧化制乙酸反应中的催化性能. 结果表明, Pd 和 SiW12 的负载顺序与 Pd 负载后的处理条件对 Pd-SiW12/SiO2 催化剂上 Pd 的分散度影响较大, 但对催化剂表面 B 酸量影响不大, 而 Pd 分散度较高时, 相应催化剂活性较高. 将 Pd 和 SiW12 同时负载于 SiO2 上时, 催化剂表现出较高的催化乙烯直接氧化制乙酸反应活性.  相似文献   

8.
用浸渍法制备了Pd/ZrO2 、Ag/ZrO2 和Co/ZrO2 等催化剂用于甲烷完全氧化反应。实验表明 ,对Pd/ZrO2 催化剂 ,焙烧温度对其催化活性影响很大 ,最佳焙烧温度为 2 80℃。对Pd/ZrO2 催化剂 ,最佳Pd负载量为 1 0w %。随总流量增大 ,甲烷转化率下降 ,随O2 /CH4进料比减小 ,甲烷转化率下降。其它负载型金属催化剂如Ag ,Co等用于甲烷氧化反应中具有一定的活性 ,但活性低于Pd。Pd -Co双金属催化剂可望是理想的Pd催化剂的替代品  相似文献   

9.
以浓硝酸处理后的多壁碳纳米管(MWCNTs)为载体,通过微波辅助法简单而快速地制备了高度分散、粒径均一的Pd/MWCNTs催化剂。利用XRD、HRTEM、XPS等手段对催化剂进行了表征。考察了Pd/MWCNTs催化剂对Heck反应的催化活性,并优化了反应温度、碱的种类和用量等反应条件。结果表明,Pd/MWCNTs在Heck反应中具有良好的催化活性。  相似文献   

10.
甲醇水蒸气重整制氢Pd/ZnO催化剂的研究   总被引:5,自引:2,他引:3  
采用并流共沉淀法制备Pd/ZnO甲醇水蒸气重整制氢催化剂,考察了Pd的质量分数和还原温度对催化剂性能的影响。结果表明,当Pd质量分数为15.9%,还原温度为573K时,催化剂有较好的甲醇转化率及二氧化碳选择性。TPR结果表明,PdO在室温下被还原为金属Pd,在440K开始有部分ZnO被还原。XRD分析结果表明,PdZn合金是甲醇水蒸气重整反应的活性中心;在21.9%Pd/ZnO催化剂上出现了Pd2Zn合金相,导致催化剂的活性下降;反应过程中还原催化剂形成PdZn合金,其活性不如相同条件下纯氢还原的。15.9%Pd/ZnO催化剂及工业铜基催化剂的初始稳定性结果显示,在8h内,15.9%Pd/ZnO催化剂上甲醇转化率保持在66%以上,而铜基催化剂的活性下降了14.4%。  相似文献   

11.
The catalytic behaviors of Pd (1.4 wt%) catalysts supported on CeO2-ZrO2-La2O3 mixed oxides with different Ce/Zr molar ratios were investigated for methanol decomposition. Nitrogen adsorption-desorption (BET), X-ray photoelectron spectroscopy (XPS), H2 temperature-programmed reduction (H2-TPR), X-ray diffraction (XRD) and Pd dispersion analysis were used for their characterization. Pd/Ce0.76Zr0.18 La0.06 O1.97 catalyst showed the highest BET surface area, best Pd dispersion capability and strongest metal-support interaction. Moreover, XPS showed that there was lattice defect oxygen or mobile oxygen. According to the result of O 1s measurements the lattice defect oxygen or mobile oxygen helped to maintain Pd in a partly oxidized state and increased the activity for methanol decomposition. The Pd/Ce0.76Zr0.18La0.06O1.97 catalyst exhibited the best activity. A 100% conversion of methanol was achieved at around 260℃, which was about 20-40 ℃ lower than other catalysts  相似文献   

12.
The catalytic behaviors of Pd (1.4 wt%) catalysts supported on CeO2-ZrO2-La2O3 mixed oxides with different Ce/Zr molar ratios were investigated for methanol decomposition. Nitrogen adsorption-desorption (BET), X-ray photoelectron spectroscopy (XPS), H2 temperature-programmed reduction (H2-TPR), X-ray diffraction (XRD) and Pd dispersion analysis were used for their characterization. Pd/Ce0.76Zr0.18 La0.06O1.97 catalyst showed the highest BET surface area, best Pd dispersion capability and strongest metal-support interaction. Moreover, XPS showed that there was lattice defect oxygen or mobile oxygen. According to the result of O 1s measurements the lattice defect oxygen or mobile oxygen helped to maintain Pd in a partly oxidized state and increased the activity for methanol decomposition. The Pd/Ce0.76Zr0.18La0.06O1.97 catalyst exhibited the best activity. A 100% conversion of methanol was achieved at around 260 °C, which was about 20-40 °C lower than other catalysts  相似文献   

13.
Methanol steam reforming, catalyzed by Pd/ZnO (PdZn alloy), is a potential source of hydrogen for on-board fuel cells. CO has been reported to be a minor side product of methanol decomposition that occurs in parallel to methanol steam reforming on PdZn catalysts. However, fuel cells currently used in vehicles are very sensitive to CO poisoning. To contribute to the understanding of pertinent reaction mechanisms, we employed density functional slab model calculations to study the decomposition of formaldehyde, a key intermediate in methanol decomposition and steam reforming reactions, on planar surfaces of Pd, Cu, and PdZn as well as on a stepped surface of PdZn. The calculated activation energies indicate that dehydrogenation of formaldehyde is favorable on Pd(111), but unfavorable on Cu(111) and PdZn(111). On the stepped PdZn(221) surface, the dehydrogenation process was calculated to be more competitive to formaldehyde desorption than on PdZn(111). Thus, we ascribe the experimentally observed small amount of CO, formed during steam reforming of methanol on the Pd/ZnO catalyst, to occur at metallic Pd species of the catalyst or at defect sites of PdZn alloy.  相似文献   

14.
ZnO对Au-Pd/CeO_2催化剂甲醇部分氧化制氢性能的影响   总被引:1,自引:0,他引:1  
采用沉积沉淀法制备了Au-Pd双金属催化剂, 研究了ZnO对Au-Pd/CeO_2催化剂甲醇部分氧化性能的影响, 并运用N_2吸附、 XRD、 UV-Vis、 TPR、 H2-TPD和CO-IR等手段对催化剂进行了表征. 结果表明, ZnO的引入减少了Pd活性中心, 降低了催化剂的活性, 但提高了催化剂H2选择性和降低了CO选择性. Au-Pd/ZnO-CeO_2催化剂的TPR表明, 在约200℃时开始有部分ZnO被还原, CO-IR显示CO吸收峰移向低频, 这些结果表明Au-Pd/ZnO-CeO_2催化剂中Pd和Zn之间发生了相互作用. Pd和Zn之间相互作用抑制了Pd的甲醇分解活性, 有利于H2和CO_2的生成, 使Au-Pd/ZnO-CeO_2催化剂表现出较高的H2选择性和较低的CO选择性.  相似文献   

15.
甲醇在CeO2担载Pd催化剂上分解机理的研究   总被引:9,自引:0,他引:9  
采用原位红外(in-situ FTIR)技术对甲醇在CeO2和Pd/CeO2催化剂上的吸附和反应进行了研究,提出一个新的甲醇分解反应机理模型。甲醇在CeO2上容易吸附并结合其晶格氧生成甲酸盐物种,而甲醇分解的产物氢被Pd活化后,溢流到CeO2上促进了甲酸盐物种的分解。C1^-的存在加强了Pd/CeO2催化剂与氢的相互作用,Pd和CeO2通过对氢和氧物种的作用对甲醇分解反应的过程表面出协同效应。  相似文献   

16.
A novel carbon‐titania composite material, C/TiO2, has been prepared by growing carbon nanofibers (CNFs) on TiO2 surface via methane decomposition using Ni‐Cu as a catalyst. The C/TiO2 was used for preparing supported palladium catalyst, Pd/C/TiO2. The support and Pd/C/TiO2 catalyst were characterized by BET, SEM, XRD and TG‐DTG. Its catalytic performance was evaluated in selective hydrogenation of citral to citronellal, and compared with that of activated carbon supported Pd catalyst. It was found that the Pd/C/TiO2 catalyst contains 97% of mesopores. And it exhibited 88% of selectivity to citronellal at citral conversion of 90% in citral hydrogenation, which was much higher than that of activated carbon supported Pd catalyst. This result may be attributed to elimination of internal diffusion limitations, which were significant in activated carbon supported Pd catalyst, due to its microporous structure.  相似文献   

17.
Pd and PdNi nanoparticles supported on Vulcan XC-72 carbon were prepared by a chemical reduction with formic acid process. The catalysts were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), cyclic voltammetry, and chronoamperometry. The results showed that the Pd and PdNi nanoparticles, which were uniformly dispersed on carbon, were 2–10 nm in diameters. The PdNi/C catalyst has higher electrocatalytic activity for methanol oxidation in alkaline media than a comparative Pd/C catalyst and shows great potential as less expensive electrocatalyst for methanol electrooxidation in alkaline media in direct methanol fuel cells.  相似文献   

18.
Catalytic decomposition of ethanol in the presence of steam over Pd supported on a porous carbonaceous material was studied. XPS and TEM were used for the catalyst characterization. Experiments were performed under atmospheric pressure, temperature of 320-360°C and H2O/C2H5OH molar ratio 8.1. It was found that the catalyst exhibited a high activity and long-term stability for the ethanol decomposition into a gas mixture containing carbon oxides, methane and hydrogen.  相似文献   

19.
The reaction mechanisms for selective acetylene hydrogenation on three different supports, Pd(4) cluster, oxygen defective anatase (101), and rutile (110) titania supported Pd(4), cluster are studied using the density functional theory calculations with a Hubbard U correction (DFT+U). The present calculations show that the defect anatase support binds Pd(4) cluster more strongly than that of rutile titania due to the existence of Ti(3+) in anatase titania. Consequently, the binding energies of adsorbed species such as acetylene and ethylene on Pd(4) cluster become weaker on anatase supported catalysts compared to the rutile supported Pd(4) cluster. Anatase catalyst has higher selectivity of acetylene hydrogenation than rutile catalyst. On the one hand, the activation energies of ethylene formation are similar on the two catalysts, while they vary a lot on ethyl formation. The rutile supported Pd catalyst with lower activation energy is preferable for further hydrogenation. On the other hand, the relatively weak adsorption energy of ethylene is gained on anatase surface, which means it is easier for ethylene desorption, hence getting higher selectivity. For further understanding, the energy decomposition method and micro-kinetic analysis are also introduced.  相似文献   

20.
采用固相-液相两步混合法制备了由碳纳米管(CNTs)和石墨烯纳米片(GNPs)组成的CNTs-GNPs复合载体。以乙二醇还原法将Pd纳米粒子沉积于复合碳载体上,制得Pd/CNTs-GNPs催化剂。以透射电子显微镜、X射线衍射及X射线光电子能谱表征催化剂的形貌、组成和结构;以电化学方法考察催化剂的甲醇电氧化性能。结果表明,Pd/CNTs-GNPs(1/4)(GNPs质量分数为1/4)催化剂具有较大的电化学表面积和较高的甲醇电氧化活性,其甲醇氧化峰电流密度可达Pd/CNTs催化剂的1.97倍。催化剂的高活性得益于CNTs-GNPs载体的一维/二维复合结构使Pd纳米粒子具有良好的分散性能。计时电流实验表明,与单一载体负载Pd催化剂相比,复合载体负载Pd催化剂具有较强的抗中毒能力。  相似文献   

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