Methane Decomposition into Carbon Fibers over Coprecipitated Nickel-Based Catalysts

Decomposition of methane in the presence of coprecipitated nickel-based catalysts to produce carbon fibers was investigated. The reaction was studied in the temperature range of 773 K to 1073 K. At 1023 K, the catalytic activities of three catalysts kept high at the initial period and then decreased with the reaction time. The lifetimes of Ni-Cu-Al and Ni-La-Al catalysts are longer than that of Ni-Al catalyst. With three catalysts, the yield of carbon fibers was very low at 773 K. The yield of carbon fibers for Ni-La-Al catalyst was more than those for Ni-Al and Ni-Cu-Al catalysts. For Ni-La-Al catalyst, the elevation of temperature from 873 K up to 1073 K led gradually to an increase in the yield of carbon fibers. XRD studies on the Ni-La-Al catalyst indicate that La2NiO4 was formed. The formation of La2NiO4 is responsible for the increase in the catalytic lifetime and the yield of carbon fibers synthesized on Ni-La-Al at 773 1073 K. Carbon fibers synthesized on Ni-Al catalyst are thin, long carbon nanotubes. There are bamboo-shaped carbon fibers synthesized on Ni-Cu-Al catalyst. Carbon fibers synthesized on Ni-La-Al catalyst have large hollow core, thin wall and good graphitization.     

Production of Hydrogen from Methane by a CO2 Emission-Suppressed Process: Methane Decomposition and Gasification of Carbon Nanofibers

Catalytic methane decomposition into hydrogen and carbon nanofibers and the oxidations of carbon nanofibers with CO₂, H₂O and O₂ were overviewed. Supported Ni catalysts (Ni/SiO₂, Ni/TiO₂ and Ni/carbon nanofiber) were effective for the methane decomposition. The activity and life of the supported Ni catalysts for methane decomposition strongly depended on the particle size of Ni metal on the catalysts. The modification of the catalysts with Pd enhanced the catalytic activity and life for methane decomposition. In particular, the supported Ni catalysts modified with Pd showed high turnover number of hydrogen formation at temperatures higher than 973 K with a high one-pass methane conversion (>70%). However, sooner or later, every catalyst completely lost their catalytic activities due to the carbon layer formation on active metal surfaces. In order to utilize a large quantity of the carbon nanofibers formed during methane decomposition as a chemical feedstock or a powdered fuel for heat generation, they were oxidized with CO₂, H₂O and O₂ into CO, synthesis gas and CO₂, respectively. In every case, the conversion of carbon was greater than 95%. These oxidations of carbon nanofibers recovered or enhanced the initial activities of the supported Ni catalysts for methane decomposition.     

催化裂解甲烷制备氢气和碳纳米纤维

采用浸渍法制备了Ni/MgO与Ni/O-D(氧化金刚石)催化剂,分别研究了反应温度和空速对甲烷催化裂解转化率的影响,并利用XPS、SEM、EDS等测试技术对催化剂进行了表征. 结果表明,33Ni/O-D和41Ni/MgO分别在500与650 ℃能长时间维持其催化活性,前者在150 min内的甲烷转化率＞8%,后者则在120 min内的甲烷转化率＞25%;甲烷初始转化率随裂解反应温度升高而增大,但温度过高导致催化剂迅速失活;降低空速有利于提高甲烷的转化率,但却会降低氢气产量;甲烷裂解生成的碳产物形貌取决于载体和催化反应条件,较低温度(500和550 ℃)下,Ni/O-D表面的裂解碳呈现出纤维状,在650 ℃以上则表现为板结颗粒堆积并将Ni完全覆盖,但该温度下的Ni/MgO表面仍能形成碳纤维,并随空速降低存在直径增加的趋势.     

Ru/CNFs 催化剂催化氨分解制氢

 研究了鱼骨式碳纤维 (CNFs) 和管式碳纤维 (CNTs) 负载 Ru 催化剂的氨分解反应活性. 结果表明, Ru/CNFs 催化剂上氨分解活性高于 Ru/CNTs 催化剂. 通过改变 Ru 负载量或载体表面的含氧基团来调节 Ru 的粒径. Ru 的活性位随着 Ru 颗粒尺寸的增大而增加. CNFs 上的含氧基团对 Ru 颗粒的氨分解活性影响很大. 在相同粒径的 Ru 颗粒上, CNFs 表面的含氧基团增加了 Ru 的活性.     

Sm修饰的Ni-MgO催化剂制备碳纳米管的研究

Carbon nanotubes (CNTs) have been synthesized over Ni-MgO and Ni-Sm-MgO catalysts by decomposition of CH₄ at 650 ℃. The addition of Sm into Ni-MgO catalyst not only promotes the catalytic activity and lifetime of the catalyst, but also improves the graphitization and heat stability of carbon nanotubes. The yield of CNTs obtained over the Ni-10Sm-MgO catalyst reaches 33 g C·(g Ni)^-1, being more than 5 times higher than that of the Ni-MgO catalyst. XRD and TPR results of the catalysts indicate that there is a remarkable interaction of Ni with Sm species, which facilitates the reduction of nickel and restrains the Ni particles from agglomerating.     

用于甲烷分解和甲烷二氧化炭重整的碳材料催化剂研究进展

The decomposition and CO2 reforming of methane,respectively,are promising alternatives to industrial steam methane reforming. In recent years,research has been focused on the development of catalysts that can operate without getting deactivated by carbon deposition,where,in particular,carbon catalysts have shown positive results. In this work,the role of carbon materials in heterogeneous catalysis is assessed and publications on methane decomposition and CO2 reforming of methane over carbon materials are reviewed. The influence of textural properties(BET surface area and micropore volume,etc.) and oxygen surface groups on the catalytic activity of carbon materials are discussed. In addition,this review examines how activated carbon and carbon black catalysts,which are the most commonly used carbon catalysts,are deactivated. Characteristics of the carbon deposits from methane are discussed and the influence of the reactivity to CO2 of fresh carbon and carbonaceous deposits for high and steady conversion during CO2 reforming of CH4 are also considered.     

Production of COx-Free Hydrogen and Few-Layer Graphene Nanoplatelets by Catalytic Decomposition of Methane over Ni-Lignin-Derived Nanoparticles

Nickel (Ni)-lignin nanocomposites were synthesized from nickel nitrate and kraft lignin then catalytically graphitized to few-layer graphene-encapsulated nickel nanoparticles (Ni@G). Ni@G nanoparticles were used for catalytic decomposition of methane (CDM) to produce COx-free hydrogen and graphene nanoplatelets. Ni@G showed high catalytic activity for methane decomposition at temperatures of 800 to 900 °C and exhibited long-term stability of 600 min time-on-stream (TOS) without apparent deactivation. The catalytic stability may be attributed to the nickel dispersion in the Ni@G sample. During the CDM reaction process, graphene shells over Ni@G nanoparticles were cracked and peeled off the nickel cores at high temperature. Both the exposed nickel nanoparticles and the cracked graphene shells may participate the CDM reaction, making Ni@G samples highly active for CDM reaction. The vacancy defects and edges in the cracked graphene shells serve as the active sites for methane decomposition. The edges are continuously regenerated by methane molecules through CDM reaction.     

载体对甲烷在镍催化剂上分解反应的影响

开发洁净廉价的燃料替代石油已成为各国竞相研究的热点。从环境友好的观点出发 ,Ｈ2 气是一种理想的洁净燃料 ,其燃烧产物只有Ｈ2 Ｏ ,对环境无任何污染 ,Ｈ2 气将成为未来人类主要的能源。因此 ,近年来各国竞相开发大规模廉价的制氢和储氢技术。目前 ,碳及碳氢化合物制合成气法[1 ,2 ] 以其成本低和技术成熟已成为当前大规模制氢最常用的方法 ,包括碳氢化合物的水蒸气重整、ＣＯ2 重整、催化部分氧化法和自热重整[1～ 4] 。近年来又兴起了甲烷催化分解制氢[5,6] 。以上各方法均包含甲烷在镍催化剂上的分解过程[7,8] 。Ｒｏｓｔｒｕｐ Ｎｉ…     

甲烷催化制氢气的研究进展

氢气作为二次能源将成为未来主要能源之一。用甲烷作原料制备氢气有重要意义。本文论述了目前国内外甲烷制氢技术的研究进展,分别对制氢的各种技术方法、反应器的分类、所用催化剂的种类及性能,以及目前解决催化剂结炭问题的研究成果等方面进行了详尽的论述。     

稀土钙钛矿型过氧化氢分解催化剂研究

柠檬酸盐热分解法合成了一系列稀土钙钛矿型过氧化氢分解催化剂，90％和30％H2O2实验表明，点火延迟时间主要取决于催化剂的润湿程度，而催化剂活性则主要取决于催化剂化学组成；所合成催化剂的活性顺序是LaNiO3〈〈LaCoO3〈LaMnO3〈LaMn0．5Co0．5O3〈LaMn0．8Co0.2O3〈La0．7Sr0．3Mn0．8Co0．2O3。为了制备商用催化剂，将30％的La0．7Sr0．3Mn0．8Co0.2O3浸渍在γ—Al2O3微球上；模拟发动机试验表明，在大于5g·cm^-2·s的较高床载荷下，催化分解89．6％的推进剂级过氧化氢的寿命达到4000s以上。     

催化剂组成和反应条件对W-Fe-MgO催化分解甲烷制备单壁碳纳米管的影响

 采用“柠檬酸法”制备的W-Fe-MgO催化剂,在小型流化床反应器中分别以Ar和H2为载气在1073～1373 K下催化甲烷分解制单壁碳纳米管(SWCNTs). 实验结果表明,用H2作载气制备SWCNTs的最佳温度为1373 K,在Fe∶Mg摩尔比≤10∶100时,催化剂上的碳产率随其W载量的增加而显著增大,产物中的SWCNTs含量也保持在较高水平,最高碳产率可达55%(相对于催化剂的质量分数). 而使用Ar载气时最佳反应温度为1073 K, 用W∶Mg摩尔比为1∶100的催化剂可制得SWCNTs含量较高的产物,而W∶Mg摩尔比超过1∶100的催化剂上产物中的SWCNTs含量显著下降. 根据XRD和XPS实验结果推测了W-Fe-MgO催化剂上生长SWCNTs的活性相.     

贵金属铂对镍基催化剂上萘转化性能的影响

 在常压连续流动固定床反应器上，以萘作为生物质气化气中焦油的模型化合物，研究了Pt对Ni／Al2O3催化剂上萘的转化率、CO和H2的选择性及收率的影响，比较了Ni－Pt／Al2O3和Ni／Al2O3两种催化剂上萘的水蒸气转化所产生的积碳量和副产物的种类，并初步考察了Ni－Pt／Al2O3催化剂上萘的水蒸气转化反应的动力学．     

用不同前驱体制备的Co/SiO2催化剂的结构及其CO2/CH4重整反应性能

 分别采用硝酸钴、醋酸钴、硫酸钴和氯化钴为前驱体制备了Co／SiO2催化剂,用XRD,TPR,SEM和H2－TPD等实验技术考察了钴盐前驱体对催化剂结构和二氧化碳重整甲烷反应性能的影响,重点考察了硝酸钴和醋酸钴的作用．结果表明,由醋酸钴制备的Co／SiO2催化剂有最佳的催化活性和稳定性,它在钴物种的存在状态、金属－载体相互作用、钴金属晶粒度及抗烧结、抗积炭能力等方面,均与由硝酸钴制备的Co／SiO2催化剂存在显著的差别．Co／SiO2催化剂的反应活性和稳定性分别与其金属分散度和抗烧结、抗积炭能力密切相关．     

Production of High Purity Multi-Walled Carbon Nanotubes from Catalytic Decomposition of Methane

Acid-based purification process of multi-walled carbon nanotubes (MWNTs) produced via catalytic decomposition of methane with NiO/TiO2 as a catalyst is described. By combining the oxidation in air and the acid refluxes, the impurities, such as amorphous carbon, carbon nanoparticles, and the NiO/TiO2 catalyst, are eliminated. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images confirm the removal of the impurities. The percentage of the carbon nanotubes purity was analyzed using thermal gravimetric analysis (TGA). Using this process, 99.9 wt% purity of MWNTs was obtained.     

Studies on the Adsorption and Dissociation of Methane and Carbon Dioxide on Nickel Catalysts

The adsorption and dissociation of methane and carbon dioxide for reforming on nickel catalysts were extensively investigated by TPSR, TPD, XPS and pulse reaction methods. These studies showed that the decomposition of methane results in the formation of at least three kinds of surface carbon species on supported nickel catalysts. Carbidic Cα, carbonaceous Cβ and carbidic clusters C-γ surface carbon species formed by the decomposition of methane demonstrated different surface mobility, thermal stability and reactivity. Carbidic Cα is a very active and important intermediate in carbon dioxide reforming with methane, and the carbidic clusters Cγ species might be the precursor of surface carbon deposition. The partially dehydrogenated Cβ species can react with H2 or CO2 to form CH4 or CO. On the other hand, it was proven that CO2 can be weakly adsorbed on supported nickel catalysts, and only one kind of CO2 adsorption state is formed. The interaction mechanism between the species dissociated from CH4     

W-Fe-MgO催化分解CH4制备单壁碳纳米管

使用“柠檬酸法”制备了一系列较高比表面的W-Fe-MgO催化剂,在较易放大的流化床反应器中,1 100 ℃ H2气流中分解CH4,制得SWCNTs管束,单管直径在1～3 nm,最高碳产率36 mg/100 mg催化剂.经TEM、微区Raman、程序升温氧化(TPO)测量表明,产物中无定形碳、MWCNTs均较少,为纯度较高、缺陷较少的SWCNTs.从EDAX结果并参考W-Fe相图推测SWCNTs生长的催化剂活性相可能为W、Fe的金属间化合物或富Fe的固溶体.     

水合肼分解产氢催化剂研究进展

氢气作为21世纪最具发展前景的清洁能源,一直备受关注.寻找安全高效的储氢材料以转型到氢能社会是当前面临的最大挑战之一.水合肼(N2H4·H2O)具有高含氢量(w=8.0％),完全分解产氢副产物仅为氮气和水,被视为一种极具应用潜力的液相化学储氢材料.开发高效、高选择性的催化剂以催化水合肼完全分解,是研究水合肼分解产氢的关...     

Rh/H-BEA催化剂上甲烷和二氧化碳的碳交换反应

 13C原位魔角旋转固体核磁共振光谱研究发现,573 K时甲烷和二氧化碳在Rh/H-BEA催化剂上发生碳交换反应. 原位红外光谱检测到HnCO(n=1,2,3)中间体,说明甲烷与二氧化碳在Rh/H-BEA上可以发生低温活化. 提出了发生碳交换反应的可能途径.     

氧化钡促进的Co/SiO2催化剂的还原性能和分解甲烷活性

 利用等体积浸渍法制备了氧化硅负载钴催化剂．通过程序升温还原、氢化学吸附、氧滴定和催化活性评价等手段研究了氧化钡对Co／SiO2的还原性能、钴分散度和颗粒度、分解甲烷活性及其稳定性等的影响．研究结果表明，氧化钡明显地影响Co／SiO2的还原性能；添加2％氧化钡提高了Co／SiO2在中温（450℃）条件下的还原度；氧化钡的还原对Co／SiO2还原的诱导、氧化钡与氧化硅及与氧化钴之间的相互作用是导致Co／SiO2还原性能变化的原因．氧化钡提高了Co／SiO2的初活性和钴的分散度，降低了钴的颗粒度；添加0．5％～1．5％氧化钡有利于提高Co／SiO2的稳定性．钴的分散度和颗粒度影响Co／SiO2的活性和稳定性；氧化钡的强供电效应也是提高Co／SiO2活性和稳定性的重要因素．甲烷分解生成的碳物种覆盖了钴活性中心，导致Co／SiO2初活性下降；但大部分碳物种并不沉积在钴活性中心上，可能形成了碳纤维生长在载体和钴活性中心之间．     

Growth of Aligned Carbon Nanotubes on Large Scale by Methane Decomposition with Deactivation Inhibitor

The effects of additives containing iron or nickel during chemical vapor deposition(CVD)on the growth of carbon nanotubes(CNTs)by methane decomposition on Mo/MgO catalyst were investigated. Ferrocene and nickel nitrate were introduced as deactivation inhibitors by in-situ evaporation during CVD. The precisely controlled in-situ introduction of these inhibitors increased the surface renewal of catalyst, and therefore prevented the catalyst from deactivation.Using this method,aligned multi-walled CNTs with parallel mesopores can be produced on a large scale.