络合还原法制备的Pd/C催化剂对甲酸氧化的电催化性能

分别以硼氢化钠和乙二醇为还原剂,经络合还原法制备了炭载钯（Pd/C）催化剂。透射电镜（TEM）和X射线粉末衍射谱（XRD）结果表明,以乙二醇为还原剂制备的Pd/C催化剂中Pd粒子具有较小的粒径、均匀的粒径分布和较大的相对结晶度,Pd粒子的平均粒径和相对结晶度分别为4.2±2 nm和1.88。电化学测试结果显示,以乙二醇为还原剂制备的Pd/C催化剂具有较大的电化学活性面积,对甲酸氧化表现出较高的电催化活性和稳定性。     

不同体系Pd/C催化剂的制备及对甲酸的电催化氧化

采用不同体系制备了碳载Pd催化剂(Pd/C),发现在乙二醇体系中制备的Pd/C催化剂对甲酸氧化具有最负的峰电位和最低的起始氧化电位,Tafel斜率最小为155mV,并且在1h的计时电流曲线测试表明,用乙二醇体系制备的Pd/C-3催化剂具有较高的稳定电流。TEM结果可以看出,用乙二醇体系制备的Pd/C催化剂Pd粒子在活性碳表面分散得最好,Pd粒径的大小约为4～5nm。     

超声辅助还原法制备钯碳催化剂及其催化Suzuki反应的研究

以椰壳活性炭为载体,乙二醇为还原剂,超声辅助还原法制备了钯碳催化剂(Pd/C-u)。利用N2物理吸附、X射线衍射分析(XRD)、透射电子显微镜(TEM)等对所制备的Pd/C催化剂进行了结构与形貌的表征,结果表明,钯纳米粒子为面心立方结构,均匀地分布在活性炭表面,平均粒径为6.16nm。当以超声辅助还原法制备Pd/C为催化剂进行对溴甲苯和对溴硝基苯与苯硼酸的Suzuki偶联反应时,在0.1%催化剂用量,60℃下反应30min时,反应收率分别为98.22%和82.08%,高于常规还原法制备的Pd/C-c催化剂。     

Pd/C催化剂制备条件优化及其在4-氨基二苯胺生产中的应用

采用浸渍法制备了Pd/C催化剂,考察了催化剂制备过程中加料方式、还原方法、载体种类、钯质量分数和浸渍液质量浓度对催化剂性能的影响,得到了制备Pd/C催化剂的优化工艺条件:载体为NH-03型活性炭,浸渍液质量浓度为20 g/L,采用滴加的方式将PdCl_2溶液加至活性炭浆液中,还原剂为(w)20%的次亚磷酸钠溶液,钯质量分数为5%。优化制备条件下制得的Pd/C催化剂用于催化加氢制备4-氨基二苯胺,表现出较好的活性,其中4-硝基二苯胺和4-亚硝基二苯胺转化率均可达到100%,4-氨基二苯胺选择性大于99%,加氢反应时间小于30 min。催化剂SEM表征结果表明:自制的Pd/C催化剂表面活性炭载体凸起部分与Pd粒子粒径相当,有利于Pd粒子在活性炭表面的负载,提高Pd粒子的吸附牢固度和分散性,进而提高了Pd/C催化剂的活性。     

Pd-TiO_2/C催化剂对甲酸的电催化氧化

用液相还原法制备Pd-TiO2/C催化剂。用循环伏安法(CV)和线性扫描法(LSV)考察了催化剂对甲酸的电催化氧化活性。通过计时电流曲线检测催化剂对甲酸的稳定性。结果表明Pd/TiO2/C催化剂中Pd粒子电化学比表面积增大,Pd-TiO2/C催化剂稳定,催化活性比Pd/C催化剂有较大幅度的提高。     

还原剂对Pd/Pb_(2-x)Mn_8O_(16)催化剂微观结构与催化性能的影响

以Hollandite型氧化物Pb_(2-x)Mn_8O_(16)为载体,Na BH4、甲醛和乙二醇为还原剂,采用液相沉积还原法制备了3种载Pd催化剂,并利用X射线衍射(XRD)、透射电子显微镜(TEM)、X射线光电子能谱(XPS)等技术对催化剂进行表征,分析了不同还原剂对催化剂微观结构、氧化还原性质及其在苯酚氧化羰基化反应中催化性能的影响。实验结果表明,Na BH4的强还原性破坏了载体Pb_(2-x)Mn_8O_(16)的结构;与甲醛相比,以乙二醇为还原剂所得的纳米钯粒子在载体上的分布更加均匀,Pd粒子的平均尺寸为4.1 nm。其中采用乙二醇为还原剂制备的Pd/Pb_(2-x)Mn_8O_(16)催化合成碳酸二苯酯的收率最高,达15.6%。     

沉积沉淀法Pd基贵金属催化剂的制备及加氢性能研究

以乙二醇为还原剂得到钯胶体后,通过沉积沉淀法制备了Pd/Al_2O_3催化剂。表征结果表明,该方法制备的Pd平均粒径为2.7 nm,远小于浸渍法制备的5nmPd粒径。将制备的Pd催化剂用于糠醛加氢反应,沉积沉淀法制备的Pd/Al_2O_3催化剂表现出了更好的催化性能,原因可以归于金属Pd的高分散性。     

纳米Pd/石墨烯-碳纳米管的制备及乙醇电氧化性能

为了提高乙醇氧化催化剂的电催化活性和稳定性,以石墨烯纳米片(GNPs)和碳纳米管(CNTs)的混合物为载体,利用微波辅助多元醇还原法制备了具有特殊空间结构的Pd/GNPs-CNTs电催化剂。透射电镜(TEM)、X-射线光电子能谱(XPS)表征结果表明,混合载体的使用改善了Pd粒子的分散性,平均粒径为3.3 nm。电化学表面积(ECSA)、循环伏安(CV)、电化学阻抗谱(EIS)、计时电流(CA)等电化学测试表明催化剂电化学表面积增大,氧化峰电流密度达到100 m A/cm2,氧化起始电位负移至-0.556 V,对乙醇氧化呈现出更高的电催化活性和更好的稳定性。     

还原法制备Pd-Ni/C阳极催化剂及其性能研究

以预处理的活性炭为载体、二氧化铈为修饰剂、NaBH_4为还原剂,制备了Pd_2Ni_3/C、Pd_(core)Ni_(shell)/C、Ni_(core)Pd_(shell)/C 3种不同结构的碱性燃料电池阳极催化剂。采用XPS、XRD、TEM表征了其结构及微观形貌,并通过电化学测试考察了其电化学性能。结果表明:NicorePdshell/C催化剂中n(Pd)∶n(Ni)=2∶3.3较接近理想比例(2∶3),催化剂颗粒分散均匀,粒径分布最窄,且平均粒径最小,为3.4 nm。电化学测试结果表明:在碱性环境下,Nicore Pdshell/C催化剂在100 m V/s扫描速度下,最高电流密度达到160 m A/cm2,在-0.5 V条件下,电流密度为2.80m A/cm2,其稳定性均优于Pd2Ni3/C和PdcoreNishell/C催化剂。     

聚吡咯碳载PdAu催化剂对甲酸的电催化氧化

通过低温氧化法制备了聚吡咯碳(PPyC),并以PPyC为载体制备了纳米Pd催化剂(Pd/PPyC)及PdAu催化剂(PdAu/PPyC),研究发现不同比例的Pd∶Au催化剂PdAu/PPyC对甲酸的甲催化活性不同。通过计算发现,催化剂的电化学比表面积催化剂中加入少量Au能够提高催化剂中活性粒子Pd的分散度,其中Pd∶Au为4∶1时电化学比表面最大,且对甲酸有最高的电催化氧化活性。     

A Facile Diethylene Glycol Reduction Method for the Synthesis of Ultrafine Pd/C Electrocatalyst with High Electrocatalytic Activity for Methanol Oxidation

The high‐quality carbon supported Pd nanoparticles (Pd/C) composites have wide applications in catalysis. In this work, we demonstrate an efficient diethylene glycol (DEG) reduction method for the synthesis of a Pd/C catalyst with high dispersion and small particle size. During the synthesis, no surfactants and halogen ions are introduced in the reaction system, and DEG efficiently acts as solvent and reducing agent, which results in a “clean” Pd surface. Meanwhile, compared to the classic ethylene glycol (EG) reduction method, the present DEG reduction method can produce the high‐quality Pd/C composites. As a result, the as‐prepared Pd/C electrocatalyst exhibits a large electrochemical active surface area and good electrocatalytic performance for the methanol oxidation reaction in an alkaline media, due to the high dispersion and small particle size. This result indicates the as‐prepared Pd/C electrocatalyst has potential applications in alkaline direct methanol fuel cells.     

Highly active carbon-supported PdNi catalyst for formic acid electrooxidation

A new carbon-supported PdNi (PdNi/C) catalyst is prepared by a simple simultaneous reduction reaction with sodium borohydride in glycol solution. The results show that the performance of PdNi/C catalyst for formic acid oxidation is greatly improved compared with that of Pd/C. X-ray diffraction (XRD) results show that Ni exists in the catalyst both as NiO and as PdNi alloy. The value of the apparent activation energy shows that the activity of formic acid oxidation on the PdNi/C is more sensitive to temperature compared with Pd/C.     

Size-controlled synthesis and impedance-based mechanistic understanding of Pd/C nanoparticles for formic acid oxidation

This work provides a detailed electrochemical impedance study for formic acid electro-oxidation on size-controlled Pd/C nanoparticles, the synthesis of which was done by a simple protocol using ethylene glycol as a reducing agent. By controlling KOH concentration, this strategy provides a synthesis method for Pd nanoparticles with a selective size range of 3.9–7.5 nm. The as-prepared Pd nanoparticles exhibited size-dependent electrochemical property and electrochemical characterizations of four different Pd/C nanocatalysts (3.9, 5.2, 6.1, and 7.5 nm) showed that Pd particle with average size of 6.1 nm has the highest formic acid oxidation activity. Electrochemical impedance-based characterizations of formic acid oxidation on Pd/C suggested that at high potentials the adsorbed oxygen species could block the catalyst surface and inhibit the oxidation reaction, as reflected by the negative polarization resistance. Unlike Pd/C, the intermediate adsorbed CO species (CO_ads) plays a critical role for formic oxidation on Pt/C and thus the impedance spectra of Pd/C and Pt/C appear different potential-dependent patterns in the second quadrant. The issue of CO was investigated by an impedance investigation of Pd/C in a mixture of formic acid containing dissolved CO.     

Synthesis of highly dispersed Pt/C electrocatalysts in ethylene glycol using acetate stabilizer for methanol electrooxidation

Pt/C electrocatalysts were prepared from a solution of H₂PtCl₆ in ethylene glycol in the presence of XC-72 carbon by adding a small amount of sodium acetate as stabilizer. Repeated TEM images showed that the platinum nanoparticles were small and uniform in size and highly dispersed on XC-72 carbon supports when a small amount of sodium acetate solution was added to the synthesis solution. The Pt/C electrocatalysts exhibited very high electrocatalytic activity for liquid methanol oxidation. The effects of adding acetate on Pt particle size and size distribution are discussed. It is demonstrated that acetate can be used as a good stabilizer for preparing Pt/C catalyst with fine and uniform Pt particles.     

厄他培南合成用钯炭催化剂制备及性能评价

以乙醇改性活性炭为载体,采用沉积-沉淀法制备10%Pd/C催化剂,考察不同还原剂对厄他培南收率及废Pd/C催化剂Pd回收率的影响。结果表明,采用硼氢化钠和水合肼还原催化剂,废Pd/C催化剂的Pd回收率大于90%,明显高于甲酸和甲醛还原的催化剂,但水合肼还原催化剂的厄他培南收率较低。     

钯炭催化剂载体对莫西沙星侧链中间体合成的影响

改进了用于莫西沙星侧链中间体合成的钯炭催化剂制备工艺,主要讨论载体材质、粒度及处理方式对催化剂性能的影响。结果表明,选择椰壳炭为载体,粒度(300~400)目,用氢氧化钠处理的载体制备的催化剂与现售催化剂相比,选择性提高2个百分点,重复使用性能提高33%。     

Au/C catalyst prepared by polyvinyl alcohol protection method for direct alcohol alkaline exchange membrane fuel cell application

An Au/C catalyst was prepared by means of the polyvinyl alcohol-protected Au sol method. Highly dispersed Au nanoparticles with an average particle size of around 3.7 nm were obtained as confirmed by transmission electron microscopy. The cyclic voltammogram of Au/C was similar to that of a bulk Au electrode, but a small shift of Au oxide reduction and oxidation potential peaks were observed. The electrooxidation of methanol, ethanol, ethylene glycol, and glycerol on the Au/C catalyst in an alkaline solution was analyzed. Using a cyclic voltammogram, the maximum current density toward alcohol electrooxidation was found to decrease in the order of glycerol > ethylene glycol > ethanol, while methanol was not oxidized. Compared with PtRu/C, the maximum current densities obtained from the Au/C catalyst for ethylene glycol and glycerol electrooxidation were increased by 1.6 and 3.3 times, respectively. The reaction heavily progressed through a C–C bond dissociation path. It was found that main product of glycerol electrooxidation was formic acid, which accounted for more than 60 % of the total product. Using chronoamperometry, the Au/C catalyst showed much better stability than that of PtRu/C for the reaction without C–C bond dissociation and better stability for the reaction with C–C bond dissociation.     

Carbon cryogel as support of platinum nano-sized electrocatalyst for the hydrogen oxidation reaction

The kinetics of hydrogen oxidation reaction was studied in perchloric acid solution on carbon-supported Pt nanoparticles using the rotating disk electrode technique. Carbon cryogel and commercial carbon black. Vulcan XC-72 were used as catalyst supports. Pt/C catalysts were prepared by a modified polyol synthesis method in an ethylene glycol (EG) solution. Considerable effect has been observed for the specific surface area of carbon support on the fundamental properties of Pt/C catalyst, such as catalyst particle size distribution and dispersion as well as catalytic activity for the oxidation of hydrogen. X-ray diffraction (XRD) and transmission electron microscopy (TEM) images show that the particle size of the catalyst decreases with the increase of specific surface area of carbon support. Cyclic voltammetry (CV) was used for determination of the actual exposed surface area of catalyst particles. It was found that Pt catalyst prepared by using the novel carbon material displayed better hydrogen electrochemical oxidation activity than the catalyst prepared by using Vulcan XC-72.     

Preparation and characterisation of carbon-supported palladium nanoparticles for oxygen reduction in low temperature PEM fuel cells

Pd nanoparticles have been synthesised using different reducing agents, including ethylene glycol (EG), formaldehyde and sodium borohydride and their activity for the oxygen reduction reaction (ORR) evaluated. The use of EG led to the best morphology for the ORR and this synthetic method was optimised by adjusting the system pH. Carbon-supported Pd nanoparticles of approximately 7 nm diameter were obtained when reduction took place in the alkaline region. Pd synthesised by EG reduction at pH 11 presented the highest mass activity 20 A g^?2 and active surface area 15 m² g^?1. These synthetic conditions were used in further synthesis. The effect of heat treatment in H₂ atmosphere was also studied; and increased size of the palladium nanoparticles was observed in every case. The Pd/C catalyst synthesised by reduction with EG at pH 11 was tested in a low temperature H₂/O₂ (air) PEMFC with a Nafion^® 112 membrane, at 20 and 40 °C. Current densities at 0.5 V, with O₂ fed to the cathode, at 40 °C were 1.40 A cm^?2 and peak power densities 0.79 W cm^?2, approximately; which compared with 1.74 A cm^?2 and 0.91 W cm^?2, respectively for a commercial Pt/C.