铈钴复合氧化物催化甲烷裂解制氢及两步法制合成气实验研究

采用共沉淀法制备了铈钴摩尔比为1：1的复合氧化物催化剂。在固定床反应器中进行了甲烷催化裂解实验,并用空气进行了催化剂失活／活化再生循环实验,利用XRD分析手段对催化剂进行了表征。结果表明,铈钴复合氧化物催化剂对甲烷裂解和积炭选择性氧化都有良好的催化性能。600℃甲烷裂解转化率达到43％,并能在280min的时间内保持活性。用空气能有效地活化已失活的催化剂,并且再生前30min积炭可被高选择性（91％）地氧化为CO,通过控制再生过程中的空气流量可以将再生后期尾气中的CO和CO2有效分离,从而分别得到较高纯度的CO和CO2。XRD结果显示,多次裂解／再生循环过程,对催化剂晶体结构没有明显破坏。     

Ni对Cu/ZnO基甲醇裂解催化剂的促进机制

通过XRD,BET,In-situ XPS等表征技术对Cu/ZnO基甲醇裂解制氢催化剂进行 了详细的研究。XRD结果表明,Cu-Zn合金的生成是Cu/ZnO基催化剂在反应初期快速 失活的主要原因;XRD,BET和N_2O滴定实验结果表明,Ni助剂可能是通过提高 Cu~0活性物种的分散度并维持Cu~0活性物种在催化反应过程中的稳定性而使 Cu/Zn/Ni催化剂的活性及稳定性大幅度提高。In-situ XPS结果表明,Ni助剂的加 入可以诱导Cu/Zn/Ni催化剂表面在甲醇裂解反应过程中出现Cu~+,从而由 Cu~0/Cu~+共同构成催化剂的活性中心,并最终导致Cu/Zn/Ni催化剂的高活性。     

流化床中甲烷裂解制氢与催化剂再生过程研究

对流化床中甲烷裂解制氢与催化剂再生过程进行了研究。选用25Ni/CuAl2O3和75Ni/CuAl2O3两种催化剂，分别在500℃和650℃进行甲烷裂解制氢与催化剂再生，反应与再生过程的温度与时间保持相同，催化剂再生时采用空气进行再生，气体流量均为370mL/min（STP）。实验结果表明,镍质量分数较低时催化剂表现出较好的稳定性，温度增加催化剂的稳定性降低。甲烷转化率随操作周期呈下降趋势，在500℃制氢与再生操作达到第五周期时，甲烷转化率趋于稳定。对切换时间的影响研究表明，切换时间存在一个最佳值，即切换5min时甲烷裂解制氢效率最高。对生成碳产品进行了XRD和TEM表征，并对实验结果进行了讨论。     

Ni/Al2 O3 催化剂上甲烷的分解温度和时间对积炭的影响

用在线质谱法研究了Ni/Al2O3催化剂上甲烷分解温度和时间对积炭的影响。实验结果表明：在600～800℃内甲烷在还原的Ni/Al2O3催化剂上可分解为表面碳物种（即NiXC）和氢气,这种表面碳物种在较低的温度下可扩散进入体相,在高温下可逐步转化为低活性的碳物种。在800℃下由于表面碳物种不能扩散进入体相,金属镍中心迅速被表面碳物种覆盖,导致甲烷分解反应失活。     

六铝酸盐SrNiAl11O19-δ催化二氧化碳重整甲烷制合成气反应研究

本文通过品格取代作用,制备了以Ni为活性组分的六铝酸盐复合氧化物催化剂SrNiAl11O19-δ并通过XRD,XPS,TPR等实验技术,对催化剂的结构和性质进行了表征.结果表明,六铝酸盐SrNiAl11O19-δ对二氧化碳重整甲烷制合成气反应具有良好的催化活性和稳定性,在780℃反应2小时,CH,和CO2转化率分别为95.0%和93.4%,没有发现活性组分Ni高温烧结和催化剂失活.     

Cu/Zn、Cu/Zn/Ni催化剂甲醇部分氧化制氢

研究了甲醇在Cu/Zn及Cu/Zn/Ni催化剂上部分氧化热耦合裂解制氢的反应,系 统地考察了不同O2/CH3OH比及反应温度下催化剂性能.当O2/CH3OH=0.2时,催化剂的性能最 佳.在同样条件下, Cu/Zn催化剂对CO的选择性较Cu/Zn/Ni催化剂低,更具优势. Cu/Zn催化 剂用于甲醇部分氧化反应时,甲醇转化率在150 h寿命实验中基本保持在90％左右. XRD谱图 表明Cu/Zn合金的生成是导致Cu/Zn系催化剂在甲醇裂解反应中快速失活的主要原因,而在部 分氧化反应中, O2的存在可抑制Cu/Zn合金的生成,使Cu/Zn催化剂表现出高度的稳定性.     

Ni晶粒粒径对Ni/SiO_2催化月桂酸甲酯脱氧制烃性能的影响

采用等体积浸渍-干燥-还原法及等体积浸渍-干燥-焙烧-还原法制备了3种具有不同Ni晶粒粒径的Ni/SiO2催化剂,利用H2-TPR、XRD、TEM、H2-TPR、NH3-TPD及TGA技术对其及前驱体进行了表征,并在固定床反应器上评价了其催化月桂酸甲酯脱氧制十一烷(C11)和十二烷(C12)的性能,分析了Ni晶粒粒径对其脱氧性能的影响。结果表明,采用等体积浸渍-干燥-还原法制备的催化剂中Ni晶粒粒径较小,提高还原温度可以促进Ni晶粒长大。随Ni晶粒粒径增大,月桂酸甲酯的转换频率提高,而C11和C12总选择性、C11/C12物质的量比及裂解产物选择性降低,Ni/SiO2催化剂上月桂酸甲酯脱氧为结构敏感反应。此外,还考察了重时空速对Ni/SiO2催化剂脱氧性能的影响,随重时空速提高,月桂酸甲酯转化率、C11和C12总选择性、C11/C12物质的量比及裂化产物选择性降低。月桂酸甲酯通过脱羰/脱羧反应路径生成的CO/CO2几乎全部加氢转化为CH4,表明Ni/SiO2催化剂具有很高的甲烷化活性。研究还发现,较小Ni晶粒烧结、有机物种吸附及积炭会导致催化剂失活。     

甲烷在稀土助剂修饰的Ni/α-Al2O3催化剂上的解离

采用脉冲－色谱法，考察了甲烷在La2O3、CeO2修饰的Ni/α-Al2O3催化剂上的解离，并用TPR、XRD等方法对催化剂进行了表征。结果表明，添加La2O3，能促进甲烷的解离，并可使解离产生的碳保持较高的活性；CeO2的添加对甲烷的解离积炭有一定的抑制作用；La2O3和CeO2均能抑制镍晶粒的聚集。甲烷在Ni基催化剂上的解离，具有一定的结构敏感性。     

二甲基二硫醚对Ni/Al_2O_3催化剂加氢性能的影响

考察了二甲基二硫醚(CH3SSCH3)对Ni/Al2O3催化剂上苯、环己烯和苯乙烯加氢活性的影响,并采用BET、XRD、H2-TPR、XPS、SEM和EA等手段对催化剂进行表征。实验结果表明,在CH3SSCH3存在下,Ni/Al2O3催化剂对苯和环己烯加氢迅速失活,且环己烯加氢对CH3SSCH3的耐硫性要略强于苯加氢,而苯乙烯中共轭烯烃的加氢转化率则维持100%长时间不变。CH3SSCH3的影响顺序为芳环单烯烃共轭烯烃。此外,通过设计实验研究了CH3SSCH3对催化剂的毒化机理,发现CH3SSCH3分子首先吸附在催化剂的表面,并发生氢解生成甲烷随尾气逸出,故CH3SSCH3分子中碳对催化剂的失活影响较小,而留下的硫原子则与镍活性组分发生相互作用,毒化催化剂。     

甲烷干重整反应用Ni-Ru/MgAl类水滑石催化剂的研究

采用焙烧记忆法分别制备Ni/Mg Al O和NiRu/Mg Al O类水滑石催化剂用于甲烷干重整反应.利用XRD、TPR、TG、XPS、CO2-TPD、TEM等表征催化剂的结构及失活特征,发现在Ni/Mg Al O中添加Ru,有利于增加催化剂表面Ni含量,并促进Ni2+的还原.不同Mg/Al比双金属催化剂中,7Ni-0.15Ru/Mg2.5Al催化剂具有较高的催化活性,这归结为该催化剂适宜的碱性、较高表面Ni含量以及小尺寸的Ni0物种.添加Ru明显抑制Ni/Mg Al O催化剂表面的丝状碳的形成.而7Ni-0.15Ru/Mg2.5Al较强的抗积碳性能与其较小Ni0晶粒尺寸及适宜催化剂碱性有关.     

Ni/Al2O3催化甲烷裂解

分别通过浸渍法和共沉淀法制备了不同Ni负载量的Ni/Al2O3催化剂。考察了Ni负载量、制备方法以及反应温度对Ni/Al2O3催化甲烷裂解性能的影响。结果表明,在550℃,浸渍法制备的Ni/Al2O3催化剂,当Ni负载量为20%(质量分数)、Ni金属平均粒径为11.25 nm时,具有最佳的甲烷催化裂解效果,其每摩尔Ni的氢气产量和每克Ni碳产量分别为164 mol和15.30 g。催化剂制备方法对Ni/Al2O3甲烷催化裂解反应有显著影响,相同Ni负载量共沉淀法制备的Ni/Al2O3甲烷催化裂解总体效果要好于浸渍法制备的Ni/Al2O3,而且反应过程中生成的碳纤维较长,管径也较均一。550℃时,共沉淀法制备的Ni负载量为41.2%(质量分数)的Ni/Al2O3催化剂在反应至350 min时,仍保持着30%以上的转化率。     

COx-Free Hydrogen and Carbon Nanofibers Produced from Direct Decomposition of Methane on Nickel-Based Catalysts

Direct decomposition of methane was carried out using a fixed-bed reactor at 700℃for the production of COx-free hydrogen and carbon nanofibers. The catalytic performance of NiO-M/SiO2 catalysts (where M=AgO, CoO, CuO, FeO, MnOx and MoO) in methane decomposition was investigated. The experimental results indicate that among the tested catalysts, NiO/SiO2 promoted with CuO give the highest hydrogen yield. In addition, the examination of the most suitable catalyst support, including Al2O3, CeO2, La2O3, SiO2, and TiO2, shows that the decomposition of methane over NiO-CuO favors SiO2 support. Furthermore, the optimum ratio of NiO to CuO on SiO2 support for methane decomposition was determined. The experimental results show that the optimum weight ratio of NiO to CuO fell at 8:2 (w/w) since the highest yield of hydrogen was obtained over this catalyst.     

Decomposition of methane over alumina supported Fe and Ni–Fe bimetallic catalyst: Effect of preparation procedure and calcination temperature

Catalytic decomposition of methane has been studied extensively as the production of hydrogen and formation of carbon nanotube is proven crucial from the scientific and technological point of view. In that context, variation of catalyst preparation procedure, calcination temperature and use of promoters could significantly alter the methane conversion, hydrogen yield and morphology of carbon nanotubes formed after the reaction. In this work, Ni promoted and unpromoted Fe/Al₂O₃ catalysts have been prepared by impregnation, sol–gel and co-precipitation method with calcination at two different temperatures. The catalysts were characterized by X-ray diffraction (XRD), N₂ physisorption, temperature programmed reduction (TPR) and thermogravimetric analysis (TGA) techniques. The catalytic activity was tested for methane decomposition reaction. The catalytic activity was high when calcined at 500 °C temperature irrespective of the preparation method. However while calcined at high temperature the catalyst prepared by impregnation method showed a high activity. It is found from XRD and TPR characterization that disordered iron oxides supported on alumina play an important role for dissociative chemisorptions of methane generating molecular hydrogen. The transmission electron microscope technique results of the spent catalysts showed the formation of carbon nanotube which is having length of 32–34 nm. The Fe nanoparticles are present on the tip of the carbon nanotube and nanotube grows by contraction–elongation mechanism. Among three different methodologies impregnation method was more effective to generate adequate active sites in the catalyst surface. The Ni promotion enhances the reducibility of Fe/Al₂O₃ oxides showing a higher catalytic activity. The catalyst is stable up to six hours on stream as observed in the activity results.     

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.     

甲烷在Ni/TiO2催化剂表面的活化

考察了Ni/TiO2催化剂甲烷部分氧化和二氧化碳重整制合成气的反应活性,实验表明,以TiO2为载体的镍系催化剂对于甲烷部分氧化制合成气反应具有较好的活性,尤其对H2的选择性较高,对二氧化碳重整制合成气反应具有较好的低温反应活性.采用脉冲-质谱在线分析等技术,在无气相氧条件下向Ni/TiO2催化剂脉冲CH4,发现甲烷在催化剂表面的活化（转化）及其氧化产物的选择性与金属催化剂表面氧的浓度密切相关.CH4与Ni/TiO2催化剂作用过程中存在明显的氢溢流和氧溢流现象,可能是这种溢流效应使得Ni/TiO2催化剂具有良好的反应活性和抗积碳性能.     

甲烷在Ni/TiO_2催化剂表面的活化

考察了Ｎｉ／ＴｉＯ２催化剂甲烷部分氧化和二氧化碳重整制合成气的反应活性,实验表明,以ＴｉＯ２为载体的镍系催化剂对于甲烷部分氧化制合成气反应具有较好的活性,尤其对Ｈ２的选择性较高,对二氧化碳重整制合成气反应具有较好的低温反应活性．采用脉冲－质谱在线分析等技术,在无气相氧条件下向Ｎｉ／ＴｉＯ２催化剂脉冲ＣＨ４,发现甲烷在催化剂表面的活化（转化）及其氧化产物的选择性与金属催化剂表面氧的浓度密切相关．ＣＨ４与Ｎｉ／ＴｉＯ２催化剂作用过程中存在明显的氢溢流和氧溢流现象,可能是这种溢流效应使得Ｎ／ＴｉＯ２催化剂具有良好的反应活性和抗积碳性能．     

流化床中 CH4/C3H8 自热重整制合成气

 在流化床反应器中, 考察了 Ni/SiO2 催化剂上 CH4 或 CH4-C3H8 临氧 CO2 重整 (自热重整) 制合成气反应性能. 结果表明, 在 CH4-C3H8 混合气自热重整反应中, Ni 粒径较小催化剂的活性和抗积炭性能较高, CH4 和 CO2 转化率分别达 75.5% 和 72.6%. C3H8 比 CH4 更易解离及被氧化, 部分 C3H8 解离出来的中间产物 CHx 物种可与吸附 H 结合为 CH4, 因而降低了 CH4 的表观转化率; CHx 也可与吸附的 CO2 物种反应生成 H2 与 CO, 从而促进了 CO2 的转化.     

Catalytic decomposition of CH4 over Ni-Al2O3-SiO2 catalysts: Influence of pretreatment conditions for the production of H2

This article reports the production of COx free hydrogen and carbon nanofibers by the catalytic decomposition of methane over Ni-Al2O3-SiO2 catalysts. The influence of reaction temperature, pretreatment temperature, and effect of reductive pretreatment on the decomposition of methane activity is investigated. The physico-chemical characteristics of fresh and deactivated samples were characterized using BET-SA, XRD, TPR, SEM/TEM, CHNS analyses and correlated with the methane decomposition results obtained. The Ni-Al-Si （4 ： 0.5 ： 1.5） catalyst reduced with hydrazine hydrate produced better H2 yields of ca. 1815 mol H2/mol Ni than the catalyst reduced with 5% H2/N2.     

Enhanced methane decomposition over transition metal-based tri-metallic catalysts for the production of COx free hydrogen

In this study, COx-free hydrogen production via methane decomposition was studied over Cu–Zn-promoted tri-metallic Ni–Co–Al catalysts. The catalysts have been prepared by the constant pH co-precipitation method, and the nominal Ni metal loading was fixed at 50 wt % along with other metals at 10 wt% each. The catalyst activity for methane decomposition reaction was examined in a reactor between 400 °C and 700 °C and at atmospheric pressure. Different techniques such as N₂-physisorption, X-ray diffraction, H₂-TPR SEM, TEM, ICP-MS, TGA, and Raman spectroscopy were applied to characterize the catalysts. The relation between the catalyst composition and their catalytic activity has been investigated. The controlled synthesis has resulted in a series of catalysts with a high surface area. Ni–Co–Cu–Zn–Al was the most active and productive catalyst. Various characterizations indicate that the promotional effects of Cu–Zn interaction were the critical factor in catalysts' activity and stability. Ni–Co–Cu–Zn catalyst gave the highest methane conversion of 85% at 700 °C. Zn addition improves the stability of the catalyst by retaining the active metal size during the decomposition reaction. The catalyst was active for 80 h of stability study. The rapid deactivation of the Ni–Co catalyst was due to the sintering of the catalyst at 650 °C. Moreover, carbon species accumulated during the methane decomposition reaction depend on the catalysts' composition. Zn promotes the growth of reasonably long and thin carbon nanotubes, whereas the diameter of carbon nanotubes on unpromoted catalysts was large.