Influence of CeO2 addition on the physicochemical and catalytic properties of Pd/TiO2 catalysts in CO oxidation

The influence of CeO₂ addition on the formation of the microstructure, electronic state, and catalytic properties of Pd/TiO₂ supported catalysts in CO oxidation were investigated. It was shown that, when Pd is supported on titanium dioxide modified with cerium dioxide, annealing at 500°C results in the formation of Pd/(CeO₂-TiO₂) catalysts with a nanocrystalline structure composed of incoherently intergrown fine anatase crystals and interblock boundaries in which palladium and cerium are stabilized. The higher catalytic activity of Pd/(CeO₂-TiO₂) catalysts compared to Pd/TiO₂ catalysts is explained by the smaller size of Pd particles and the higher proportion of palladium in the Pd^δ+ state.     

Preparation and Catalytic Performance of Carbon Nanotube Supported Palladium Catalyst

Two carbon nanotube supported palladium catalysts were prepared using a chemical reduction technique (Pd/CR‐CNT) and a conventional impregnation method (Pd/CNT) respectively, and their catalytic performances for Heck reaction were investigated. The catalysts were characterized by TEM and XPS techniques and the products were characterized by ¹H NMR. Research results showed that the (Pd/CR‐CNT) catalyst showed a better catalytic activity than the (Pd/CNT) catalyst, owing to better dispersion of palladium nanoparticles and stronger interaction between the active palladium species and carbon nanotube. Meanwhile, the product yield maintained 99.93% of its initial value at five‐times re‐use, compared with that at the first time use. The catalyst prepared with the chemical reduction method represented a better reusing performance.     

负载Pd密偶催化剂的载体效应

采用尿素水解法或吸附沉淀法制备了金属氧化物载体,并用浸渍法负载0.5%Pd制得了Pd/Sn0.4Zr0.6O2,Pd/ZrO2,Pd/SnO2,Pd/SnO2-Al2O3和Pd/Al2O3催化剂.采用原位漫反射红外光谱、拉曼光谱、X射线光电子能谱和程序升温还原等方法对催化剂结构进行了表征,探讨了不同载体对表面PdOx物种化学吸附性质和氧化还原性能的影响,并与样品的丙烷氧化活性相关联.漫反射红外光谱表明,在Pd/SnO2-Al2O3中,Sn对Al2O3表面的Pd原子簇起到稀释作用,促进了Pd的分散,使得其CO线式吸附强度明显高于Pd/Al2O3,但Pd过高的分散度不仅减少了表面Pd-PdO活性位对的数目,而且使反应中间物种Pd-OH之间脱水困难,因而阻塞了活性位,降低了其循环氧化还原活性;而在Sn0.4Zr0.6O2复合氧化物载体中,SnO2有效地阻止了四方晶相ZrO2向稳态单斜晶相转变,且复合载体的比表面积较ZrO2和SnO2有所增加,其表面PdOx物种的分散度适中.此外,Sn0.4Zr0.6O2复合氧化物负载的Pd的价态介于Pd0与Pd2 之间,表面氧空位较多,促进了丙烷中C-H键的活化,使比表面积较低的Pd/Sn0.4Zr0.6O2具有最好的催化丙烷氧化能力,相反比表面积较高的Pd/SnO2-Al2O3活性很差,说明分散度适中且具有较低氧化态的PdOx(0相似文献   

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

The activity and thermal stability of Pd/Al2O3 and Pd/（Al2O3＋MOx） （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 aluminasupported 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/Al2O3. The improvement of the palladium activity by lanthanum and cerium support modifier was observed only at low temperatures of the reaction.     

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.     

Effect of support on activity of palladium catalysts in nitrobenzene hydrogenation

The effect of two types of catalysts on the activity of the catalytic hydrogenation of nitrobenzene was studied. Catalysts were prepared by the surface deposition of palladium hydroxide with a simultaneous reduction with formaldehyde in a basic environment and were characterised by X-ray powder diffraction, transmission electron microscopy, adsorption-desorption, and catalytic tests — hydrogenation of nitrobenzene in methanol. The influence of the supports’ (activated carbon and a mixture of activated carbon and multi-walled carbon nanotubes) surface area is discussed. Despite having a size comparable (4–5 nm) to crystallites of metallic palladium, the catalyst prepared on a mixture of activated carbon and nanotubes (Pd/C/CNT) was significantly less active than the catalyst prepared on pure activated carbon (Pd/C); the rate of this reaction was approximately 30 % lower than the initial reaction rate. This feature could be attributed to the lower specific surface area of the Pd/C/CNT (531 m² g^?1) in comparison with the Pd/C (692 m² g^?1).     

BEHAVIOR OF SUPPORTED NANO-COPPER CATALYST IN CO OXIDATION

IntroductionNanomaterialisanewkindofmaterialwithparticlesizebetWeenIurnand100urn.Becauseofthesmallparticlesizeandthelargespecificsufficearea,nanomaterialpossessesmanyparticularproperties,suchashighersufficeenergyandhighersurfaceactivity.t.[l]Thehigheracti…     

Fabrication of Nitrogen‐Doped Mesoporous‐Carbon‐Coated Palladium Nanoparticles: An Intriguing Electrocatalyst for Methanol and Formic Acid Oxidation

Inspired by the attractive catalytic properties of palladium and the inert nature of carbon supports in catalysis, a concise and simple methodology for in situ nitrogen‐doped mesoporous‐carbon‐supported palladium nanoparticles (Pd/N‐C) has been developed by carbonizing a palladium dimethylglyoximate complex. The as‐synthesized Pd/N‐C has been exfoliated as a fuel cell catalyst by studying the electro‐oxidation of methanol and formic acid. The material synthesized at 400 °C,namely, Pd/N‐C‐400,exhibitssuperior mass activity and stability among catalysts synthesized under different carbonization temperaturesbetween300 and 500 °C. The unique 1D porous structure in Pd/N‐C‐400 helps better electron transport at the electrode surface, which eventually leads to about five times better catalytic activity and about two times higher stability than that of commercial Pd/C. Thus, our designed sacrificial metal–organic templatedirected pathway becomes a promising technique for Pd/N‐C synthesis with superior catalytic performances.     

Pd/C promoted by Au for 2-propanol electrooxidation in alkaline media

Pd/C catalysts promoted by Au are investigated as electrocatalysts for the direct 2-propanol fuel cells in alkaline media. The results show that Pd is a good electrocatalyst for 2-propanol oxidation and the activity for 2-propanol electrooxidation is higher than that for methanol electrooxidation on the Pd/C electrocatalysts in alkaline media. Addition of Au can significantly increase the palladium catalytic activity and stability for the 2-propanol oxidation. PdAu4:1/C has higher electrocatalytic activity and better stability for the electrooxidation of 2-propanol than Pd/C and E-TEK Pt/C electrocatalysts. The present study shows the promising properties of Au promoted Pd/C as effective electrocatalysts for 2-propanol fuel based direct alcohol fuel cells.     

Catalytic oxidation of glyoxal to glyoxalic acid over Au-Pd alloy nanoparticles on hydrotalcite

Synthesis of glyoxalic acid by selective oxidation of glyoxal at ambient temperatures with O₂ as an oxidant is an important problem. We found that gold nanoparticles supported on hydrotalcite (Au/HT) exhibit an appreciable catalytic activity for this reaction in the liquid phase. Moreover, Au-Pd/HT, prepared by the deposition-precipitation method is superior in the catalytic behavior to monometallic Au/HT and Pd/HT catalysts. Introduction of palladium enhances ability of the catalysts to oxidize carbonyl to carboxyl, weakens the power to rupture C-C bond and in this way improves the catalytic performance. Furthermore, the Au: Pd ratio also influences the properties of the alloy catalysts. The 1.5Au-1.5Pd/HT catalysts show the highest activity for the selective oxidation at ambient temperature producing glyoxalic acid in 13.4% yield at pH 7.7. Moreover, due to basic properties of hydrotalcite, glyoxalic acid could be synthesized over 1.5Au-1.5Pd/HT in 8.0% yield without adding a base. It is hoped that results of this study can fuel further research in designing new catalysts with alloy nanoparticles supported by hydrotalcite that can be used for the selective oxidation of other useful compounds.     

PtRu/carbon nanotube nanocomposite synthesized in supercritical fluid: a novel electrocatalyst for direct methanol fuel cells

Platinum/ruthenium nanoparticles were decorated on carbon nanotubes (CNT) in supercritical carbon dioxide, and the nanocomposites were characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). TEM images show that the particles size is in the range of 5-10 nm, and XRD patterns show a face-centered cubic crystal structure. Methanol electrooxidation in 1 M sulfuric acid electrolyte containing 2 M methanol were studied onPtRu/CNT (Pt, 4.1 wt%; Ru, 2.3 wt%; molar ratio approximately Pt/Ru = 45:55) catalysts using cyclic voltammetry, linear sweep voltammetry, chronoamperometry, and electrochemical impedance spectroscopy. All the electrochemical results show that PtRu/CNT catalysts exhibit high activity for methanol oxidation which resulted from the high surface area of carbon nanotubes and the nanostructure of platinum/ruthenium particles. Compared with Pt/CNT, the onset potential is much lower and the ratio of forward anodic peak current to reverse anodic peak current is much higher for methanol oxidation, which indicates the higher catalytic activity of PtRu/CNT. The presence of Ru with Pt accelerates the rate of methanol oxidation. The results demonstrated the feasibility of processing bimetallic catalysts in supercritical carbon dioxide for fuel cell applications.     

Pd/NaZSM-5负载型催化剂上CO完全氧化研究

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。     

Palladium catalysts deposited on silicon nitride in the deep oxidation of methane

The physicochemical and catalytic properties of palladium catalysts were studied in the deep oxidation of methane. The catalysts were deposited on silicon nitride from aqueous (Pd/Si₃N₄-a) and toluene (Pd/Si₃N₄-t) solutions of palladium acetate. The use of aqueous and organic solutions of palladium acetate, all other preparation conditions being equal, resulted in the formation of palladium systems with different catalytic properties. The sample from Pd/Si₃N₄-t was characterized by high activity and stability. The systems studied had different structures and adsorption properties of palladium nanoparticles, which influenced the form of reagent adsorption, catalytic properties, and mechanism of surface reactions. The suggestion was made that the solvent played a key role in the formation of the active surface of Pd-containing catalytic systems.     

Pd/WO_3-RGO纳米催化剂对甲酸氧化的电催化性能

采用表面修饰技术将WO_3晶粒引入到氧化石墨烯(GO)表面,通过硼氢化钾还原法制备了载钯催化剂Pd/WO_3-RGO.对催化剂进行了结构和形貌表征,并考察了该催化剂对甲酸氧化的电催化性能.结果表明,Pd/WO_3-RGO催化剂由石墨烯、单斜态WO_3和立方面心Pd晶粒组成,Pd颗粒均匀分散在载体上;使用Pd/20%WO_3-RGO催化剂电极时的甲酸氧化最大峰电流密度大幅增加,是Pd/RGO催化剂电极甲酸氧化峰电流密度的2.5倍;Pd/WO_3-RGO催化剂稳定性大大增强,且具有更加优异的抗CO中毒能力;Pd晶粒与WO_3晶粒的相互交叠有利于它们之间的催化协同效应,增强催化剂的催化性能.     

配位体对钯纳米催化剂的形成及其电活性的影响

分别在EDTA,甘氨酸(Gly)和木质素磺酸钠(Ls)存在下,以硼氢化钠为还原剂,将Pd²⁺还原为Pd纳米颗粒并负载在多壁碳纳米管(MWCNT)表面。采用扫描电镜(SEM),透射电镜(TEM)和X射线衍射(XRD)对纳米Pd催化剂的形貌和微结构进行了表征。结果表明:EDTA存在时,所形成的Pd纳米颗粒(Pd-EDTA/MWCNT)的粒径更小,在MWCNT上的分散度更高。采用循环伏安(CV)和计时伏安技术(CA),研究了催化剂在碱性环境中对乙醇的电催化活性。在碱性溶液中对乙醇氧化的电化学研究表明:在Pd-EDTA/MWCNT催化剂上,乙醇氧化反应的起始电位较低,电流密度最大,电子传递阻力较小,反应速率较大,并且对乙醇氧化的电催化活性保持稳定。     

二氧化碳在Pd/SiO2和La-Pd/SiO2上的催化氢化反应

对CO₂在附载型Pd催化剂上的氢化反应的研究迄今报道不多^[1,2],且都在加压条件下进行,对常压下助催剂如何改善Pd的催化行为未见报道。本文探讨了Pd/SiO₂催化剂,未加与掺加助催剂La(NO₃)₃后,其Pd粒大小、CO₂的吸附性能及CO₂/H₂催化活性等方面都有显著差异。     

Defect Rich Structure Activated 3D Palladium Catalyst for Methanol Oxidation Reaction

Controlling the structure and properties of catalysts through atomic arrangement is the source of producing a new generation of advanced catalysts. A highly active and stable catalyst in catalytic reactions strongly depends on an ideal arrangement structure of metal atoms. We demonstrated that the introduction of the defect-rich structures, low coordination number (CN), and tensile strain in three-dimensional (3D) urchin-like palladium nanoparticles through chlorine bonded with sp-C in graphdiyne (Pd-UNs/Cl-GDY) can regulate the arrangement of metal atoms in the palladium nanoparticles to form a special structure. In situ Fourier infrared spectroscopy (FTIR) and theoretical calculation results show that Pd-UNs/Cl-GDY catalyst is beneficial to the oxidation and removal of CO intermediates. The Pd-UNs/Cl-GDY for methanol oxidation reaction (MOR) that display high current density (363.6 mA cm⁻²) and mass activity (3.6 A mg_Pd⁻¹), 12.0 and 10.9 times higher than Pd nanoparticles, respectively. The Pd-UNs/Cl-GDY catalyst also exhibited robust stability with still retained 95 % activity after 2000 cycles. A defects libraries of the face-centered cubic and hexagonal close-packed crystal catalysts (FH-NPs) were synthesized by introducing chlorine in graphdiyne. Such defect-rich structures, low CN, and tensile strain tailoring methods have opened up a new way for the catalytic reaction of MOR.     

STUDIES ON THE CATALYTIC REACTION OF NITROGEN OXIDE ON METAL MODIFIED ACTIVATED CARBON FIBERS

The catalytic reaction of NO with CO and decomposition of NO over metal modified ACFs were investigated and compared with other carriers supported catalysts. It is demonstrated that Pd/ACF and Pd/Cu/ACF have high catalytic activity for the reaction of NO/CO, while Pt/ACE. Pt/Cu/ACF and Co/Cu/ACF have very low catalytic activity in similar circumstance. Pd-modified ACF possesses high catalytic decomposition of NO at 300℃. Pd/CB and Pd/GAC present good catalytic decomposition abifity for NO only at low [lowrate. Pd/G Pd/ZMS and Pd/A however, do not show any catalytic activity for NO decomposition even at 400 ℃. Catalytic temperature, NO flowrate and loading of metal components affect the decomposition rate of NO. The coexistence of Cu with Pd on Cu/Pd/ACF leads to crystalline of palladium to more unperfected so as to that increase the catalytic activity.     

还原剂对Au-Pd/CeO2催化剂甲醇部分氧化性能的影响

以PVP为保护剂,乙醇(ER)、乙二醇(GR)和水合肼(HR)为还原剂制备了一系列Au-Pd/CeO2催化剂,考察了还原剂对甲醇部分氧化性能的影响,并运用XRD、TPD和TPR等手段对催化剂进行了表征。结果表明,Au-Pd/CeO2(ER)催化剂具有较大的比表面积,形成的AuxPdy量较多、粒径较小、分散度较高、活性组分与载体的相互作用较强,同时对甲醇的吸附量较大和吸附温度较低。因此,该催化剂具有较高的催化活性和氢气选择性以及较低的CO质量分数。     

Catalytic activity of palladium supported on single wall carbon nanotubes compared to palladium supported on activated carbon Study of the Heck and Suzuki couplings, aerobic alcohol oxidation and selective hydrogenation

Nanoparticles (2–10 nm) of palladium have been deposited on single wall carbon nanotubes (SWNT) by spontaneous reduction from Pd(OAc)₂ or from oxime carbapalladacycle. These catalysts exhibit higher catalytic activity than palladium over activated carbon (Pd/C) for the Heck reaction of styrene and iodobenzene and for the Suzuki coupling of phenylboronic and iodobenzene. This fact has been attributed as reflecting the dramatic influence of the size particle on the activity of the palladium catalyst for CC bond forming reactions as compared to other reaction types less demanding from the point of view of the particle size. Thus, in contrast to the Heck and Suzuki reactions, Pd/C is more active than palladium nanoparticles deposited on SWNT for the catalytic oxidation by molecular oxygen of cinnamyl alcohol to cinnamaldehyde and for the hydrogenation of cinnamaldehyde to 3-phenylpropionaldehyde.