Effects of sol-gel method and lanthanum addition on catalytic performances of nickel-based catalysts for methane reforming with carbon dioxide

The nickel-based catalysts were prepared by the sol-gel method and used for the CH4 reforming with CO2. The effects of the sol-gel method on the specific surface area, catalytic activity, desorption, and reduction performances of catalysts were investigated with BET, TPR, and TPD. Compared with the catalyst prepared by the impregnation method, the results indicated that the catalysts prepared by the sol-gel method had larger specific surface area, showing higher catalytic activities and exhibiting perfect desorption and reduction performances. In addition, the modification effects of adding La were studied, and it was found that the 0.75NLBT catalyst constituted of 5wt.%Ni-0.75wt.%La was optimal.

Methane Decomposition into Carbon Fibers over Coprecipitated Nickel-Based Catalysts

Decomposition of methane in the presence of coprecipitated nickel-basedcatalysts to produce carbon fibers was investigated. The reaction was studied in the temperaturerange of 773 K to 1073 K. At 1023 K, the catalytic activities of three catalysts kept high at theinitial period and then decreased with the reaction time. The lifetimes of Ni-Cu-Al and Ni-La-Alcatalysts are longer than that of Ni-Al catalyst. With three catalysts, the yield of carbon fiberswas very low at 773 K. The yield of carbon fibers for Ni-La-Al catalyst was more than those forNi-Al and Ni-Cu-Al catalysts. For Ni-La-Al catalyst, the elevation of temperature from 873 K up to1073 K led gradually to an increase in the yield of carbon fibers. XRD studies on the Ni-La-Alcatalyst indicate that La_2NiO_4 was formed. The formation of La_2NiO_4 is responsible for theincrease in the catalytic lifetime and the yield of carbon fibers synthesized on Ni-La-Al at773-1073 K. Carbon fibers synthesized on Ni-Al catalyst are thin, long carbon nanotubes. There arebamboo-shaped carbon fibers synthesized on Ni-Cu-Al catalyst. Carbon fibers synthesized on Ni-La-Alcatalyst have large hollow core, thin wall and good graphitization.

Autothermal Reforming of Methane over Ni Catalysts Supported on CuO-ZrO_2-CeO_2-Al_2O_3

Ni catalysts supported on various mixed oxides of Al2O3 with rare earth oxide and transitional metal oxides were synthesized. The studies focused on the measurement of the autothermal reforming of methane to hydrogen over Ni catalysts supported on the mixed oxide ZrxCe30-xAl70Oδ （x-=5, 10, 15）. The catalytic performance of Ni/Zr10Ce20Al70Oδ was better than that of other catalysts. XRD results showed that the addition of Zr to Ni/Ce30Al70Oδ prevented the formation of NiAl2O4 and facilitated the dispersion of NiO. Effects of CuO addition to Zr10Ce20Al70Oδ were also investigated. The activity of Ni catalyst supported on CuO-ZrO2-CeO2-Al2O3 was somewhat affected and the Ni/Cu5Zr10Ce20Al65Oδ showed the best catalytic performance with the highest CH4 conversion, yield of H2, selectivity for H2 and H2/CO production ratio in operation temperatures ranging from 650 to 750 ℃.

Steam reforming of acetic acid over Ni-Ba/Al2O3 catalysts:Impacts of barium addition on coking behaviors and formation of reaction intermediates

The influence of barium addition to a Ni/Al2O3 catalyst on the reaction intermediates formed,the activity,resistance of the catalyst to coking,and properties of the coke formed after acetic acid steam reforming were investigated in this study.The results showed the drastic effects of barium addition on the physicochemical properties and performances of the catalyst.The solid-phase reaction between alumina and BaO formed BaAl2O4,which re-constructed the alumina structure,resulting in a decrease in the specific surface area and an increase in the resistance of metallic Ni to sintering.The addition of barium was also beneficial for enhancing the catalytic activity,resulting from the changed catalytic reaction network.The in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) study of the acetic acid steam reforming indicated that barium could effectively suppress the accumulation of the reaction intermediates of carbonyl,formate,and C=C functional groups on the catalyst surface,attributed to its relatively high ability to cause the gasification of these species.In addition,coking was considerably more significant over the Ba-Ni/Al2O3 catalyst.Moreover,the Ba-Ni/Al2O3 catalyst was more stable than the Ni/Al2O3catalyst,owing to the distinct forms of coke formed (carbon nanotube form over the Ba-Ni/Al2O3 catalyst,and the amorphous form over the Ni/Al2O3 catalyst).

Synthesis and Crystal Structure of a New Nickel(II) Complex with Unsymmetric Quadridentate Schiff Base Containing Oxime

The title complex, C18H15N3NiO3, has been prepared and characterized by X-ray diffraction analysis. It crystallizes in the monoclinic system, space group Cc with a = 10.939(2), b = 22.909(5), c = 6.907(1) ?, β = 116.75(3)°, V = 1545.7(5) ?, Z = 4, Mr = 380.04, F(000) = 784, Dc = 1.633 g/cm3 and μ(MoKα) = 1.279 mm–1. The structure was refined to R = 0.0472 and wR = 0.0893 for 2571 observed reflections with I > 2σ(I). The absolute structure Flack parameter X is 0.01(2). In this crystal structure, strong face-to-face π-π stacking interactions between adjacent molecules lead to a one-dimensional chain structure.

Effect of CeO_2 and CaO Promoters on Ignition Performance for Partial Oxidation of Methane over Ni/MgO-Al_2O_3 Catalyst

The effect of CeO2 and CaO promoters on the ignition performance over Ni/MgO-Al2O3 catalyst for the partial oxidation of methane （POM） to synthesis gas was investigated. It was found that the POM reaction could not be ignited over lwt%Ni/MgO-Al2O3 catalyst without the promoters in the temperature range from 773 K to 1073 K. CeO2 and CaO promoters enhanced the ignition performance and the POM reactivity of lwt%Ni/MgO-Al2O3 catalyst remarkably. Moreover, the improving effect became greater with the increase of the promoter content under the investigated reactiorrconditions. The modification effects of CeO2 and CaO promoters were closely related to the concentration and reducibility of the surface and bulk oxygen species.

Improved catalytic performance of Ni catalysts for steam methane reforming in a micro-channel reactor

Milliseconds process to produce hydrogen by steam methane reforming （SMR） reaction, based on Ni catalyst rather than noble catalyst such as Pd, Rh or Ru, in micro-channel reactors has been paid more and more attentions in recent years. This work aimed to further improve the catalytic performance of nickel-based catalyst by the introduction of additives, i.e., MgO and FeO, prepared by impregnation method on the micro-channels made of metal-ceramic complex substrate. The prepared catalysts were tested in the same micro-channel reactor by switching the catalyst plates. The results showed that among the tested catalysts Ni-Mg catalyst had the highest activity, especially under harsh conditions, i.e., at high space velocity and/or low reaction temperature. Moreover, the catalyst activity and selectivity were stable during the 12 h on stream test even when the ratio of steam to carbon （SIC） was as low as 1.0. The addition of MgO promoted the active Ni species to have a good dispersion on the substrate, leading to a better catalytic performance for SMR reaction.

Ethanol steam reforming over Ni-Cu/Al_2O_3-M_yO_z (M = Si, La, Mg,and Zn) catalysts

Ni-based catalysts doped with copper additives were studied on their role in ethanol steam reforming reaction. The effects of Cu content, support species involving Al2O3-SIO2, Al2O3-MgO, Al2O3-ZnO, and Al2O3-La2O3, on the catalytic performance were studied. Characterizations by TPR, XRD, NH3-TPD, XPS, and TGA indicated that catalysts 30Ni5Cu/Al2O3-MgO and 30Ni5Cu/Al2O3-ZnO have much higher H2 selectivity than 30Ni5Cu/Al2O3-SiO2, as well as good coke resistance. H2 selectivity for 30Ni5Cu/Al2O3-MgO catalyst was 73.3% at 450 ℃ and increased to 94.0% at 600℃, whereas for 30Ni5Cu/Al2O3-ZnO catalyst, the H2 selectivity was 63.6% at 450 ℃ and 95.2% at 600℃. TheseAl2O3-MgO and Al2O3-ZnO supported Ni-Cu bimetallic catalysts may have important applications in the production of hydrogen by ethanol steam reforming reactions.

Kinetics modeling for the mixed reforming of methane over Ni-CeO_2/MgAl_2O_4 catalyst

Kinetics model was developed for the mixed （steam and dry） reforming of methane, which is useful for the control of H2/CO ratio. The equilibrium constants of reaction rate were determined using the experimental equilibrium data at different reaction temperatures, while the forward reaction rate constants were estimated using the experimental data under non-equilibrium （high inert fraction and high space velocity） conditions. The comparison between calculated and experimental data clearly showed that the developed model described satisfactorily, and further analysis using the parametric sensitivity determined the wall temperature and CO2 fraction in the feed gas as effective parameters for the manipulation of CH4 conversion and H2/CO ratio of synthesis gas under the equilibrium condition. Meanwhile, the inert fraction, rather than the residence time, was selected as additional parameter under non-equilibrium condition.

3D-Ni_(3)S_(2)微球电催化尿素氧化辅助制氢研究

电催化尿素氧化(UOR)替代动力学缓慢的析氧反应(OER)为高效制氢提供了新的思路。本研究通过简单的二次水热法制备了三维Ni_(3)S_(2)/NF微球催化剂(3D-Ni_(3)S_(2)/NF),由于独特的3D结构为UOR提供了高度开放的活性区域,并加快了电荷转移速率,3D-Ni_(3)S_(2)/NF表现出明显优于1D,2D-Ni_(3)S_(2)/NF电催化氧化尿素的活性。在1 mol L^(-1)KOH+0.33 mol L^(-1)尿素电解质溶液,3D-Ni_(3)S_(2)/NF电催化尿素氧化达到100 mA cm^(-2)的电流密度的电位仅需1.38 V vs.RHE,比OER电位减少了250 mV,同时在24 h稳定性测试中表现出良好的耐久性。此外,全尿素辅助制氢只需1.66 V即可达到50 mA cm^(-2),表现出比传统电解水(1.86 V)更低的电位。

偏三甲苯液相空气氧化制偏苯三酸Ni-Mn-Br-Zr催化剂的研究

针对Co-Mn-Br-Zr催化剂氧化性强导致副产多的问题,以氧化性稍弱的Ni-Mn-Br-Zr为催化剂探究催化剂各组分摩尔比对偏三甲苯液相空气氧化生成偏苯三酸反应的影响,同时与Co-Mn-Br-Zr催化剂在相同条件下进行比较。结果表明,随着Ni、Mn摩尔分数的增大,偏三甲苯的转化率、偏苯三酸摩尔收率都有所提高,同时副产物苯二甲酸和均苯四酸的收率也随之增加;随着Br摩尔分数的增大,偏三甲苯转化率迅速增大,但偏苯三酸摩尔收率仅有略微增大;Zr摩尔量变化对反应几乎没有影响。在200℃、2.0 MPa、Ni(Co)∶Mn∶Br∶Zr摩尔比为1∶1∶1∶0.05、反应时间为80 min的条件下,Ni基催化剂下偏苯三酸的摩尔收率达到了56.60%,杂质酸收率为3.16%;优于Co基催化剂下偏苯三酸的摩尔收率54.85%和杂质酸收率3.66%。

天然气-二氧化碳-水蒸气-氧转化制合成气的研究——稀土助剂的作用

研究了稀土氧化物 (CeO2 和La2 O3)改性的镍基催化剂中助剂的作用 ,并考察了催化剂对天然气 二氧化碳 水蒸气 氧转化制合成气反应的活性 .结果表明 ,La2 O3 改性的镍基催化剂具有较高的CH4 转化率和H2 选择性 ;经CeO2 改性的镍基催化剂具有较高的CO选择性 .量子化学计算和XRD研究结果表明 ,La2 O3 助剂的加入 ,可使还原后催化剂表面Ni(111)晶面衍射峰的强度减小 ,较好地符合吸附活化CH4 分子的“尺寸效应”和能量要求 .添加CeO2 助剂的催化剂 ,其Ni(111)晶面衍射峰强度较大 ,而Ni(110 )晶面含量最小 ,不利于CH4 的离解 .同时 ,助剂RE2 O3(尤其是CeO2 )和MgO提高了Ni的d电子密度 ,因而一定程度上加强了Nid电子向CO2 空反键π轨道的迁移 ,促进CO2 分子的活化 。

非负载镍催化剂的2-乙基蒽醌加氢活性及其氢吸脱附性质

分别制备了金属镍粉、兰尼镍、Ni B非晶态合金及镧掺杂的Ni B非晶态合金 (Ni B La)催化剂 ,研究了催化剂的氢吸附和脱附性质以及对 2 乙基蒽醌加氢反应的催化性能 .结果表明 ,金属镍粉、兰尼镍和Ni B催化剂表面均具有两种氢吸附位 :弱吸附位和强吸附位 .Ni B La催化剂表面只有氢的强吸附位 ,其强吸附氢量与兰尼镍相当 .推测只有氢的强吸附位是 2 乙基蒽醌加氢反应的活性中心 ,并且Ni B La催化剂上的强吸附氢较兰尼镍上的更活泼 ,因而Ni B La非晶态合金催化剂对加氢反应的催化活性高于兰尼镍 .

等离子体技术制备Ni/α-Al_2O_3催化剂

采用射频辉光放电等离子体技术制备了用于天然气部分氧化制合成气反应的α Al2 O3担载金属Ni催化剂。考察了该催化剂的反应活性、稳定性 ,并与常规方法制备的催化剂进行了比较。结果表明 ,采用等离子体技术制备的催化剂 ,具有操作简便、工艺流程短、催化剂变化过程直观易控、催化剂活性高、稳定性好等优点 ,在 850℃反应时可获得 98 2 %天然气转化率 ,97 3%H2 选择性和 96 5%CO选择性 ,并且反应 1 5h后催化剂活性几乎未下降。XRD和TPR实验结果表明 ,采用等离子体技术制备的催化剂的晶相组成和还原性能与常规催化剂有很大差别。

热处理对高硫化氢合成气一步法制甲硫醇K2MoO4-NiO/SiO2催化剂结构及性能的影响

在不同焙烧温度和焙烧气氛下对共浸渍法制备的K2MoO4-NiO/SiO2催化剂进行热处理,并采用X射线衍射、热重-差示扫描量热、氢气程序升温还原、拉曼光谱和电子自旋共振波谱等手段对催化剂进行了表征,同时考察了催化剂催化高硫化氢合成气一步法制甲硫醇的性能.结果表明,由于催化剂中所含柠檬酸氧化放热,空气中焙烧的催化剂发生严重烧结.随着焙烧温度的升高,八面体配位的Mo(Oh)逐渐向四面体配位的Mo(Td)转变,导致催化剂的还原能力降低,配位不饱和Mo(CO吸附位)减少,因而CO转化率降低.甲硫醇的生成与Mo–S–K相密切相关,而MoS2晶相表面主要生成烃类.与氮气中焙烧的催化剂相比,空气中焙烧的催化剂表面的MoS2相较多,而Mo–S–K相较少,因此具有更高的烃类选择性和更低的甲硫醇选择性.

无模板剂一锅法合成介孔Ni-CaO-ZrO_2催化剂及其在CH_4-CO_2重整反应中的应用研究

通过无模板剂一锅法制备出一种具有较大比表面积和孔容的介孔Ni-CaO-ZrO2催化剂,并将其用于CH4-CO2重整反应过程。利用N2吸附-脱附(BET)、SEM、TEM、X射线粉末衍射(XRD)、程序升温还原(H2-TPR)以及热重(TG)等手段对催化剂进行了表征。结果表明,该催化剂具有较强的金属-载体相互作用,这种强金属-载体相互作用(SMSI)使Ni与载体紧密接触,有利于吸附物种在界面进行快速反应,使催化剂在反应过程中具有较高的反应活性和稳定性。虽然反应后的催化剂表面有一定量的积炭生成,但这些积炭多以丝状碳为主,并不会覆盖催化剂的活性位点。

乙烯齐聚合成线性α-烯烃镍系催化剂

利用SHOP型工艺由乙烯齐聚制备线性α-烯烃不仅具有工业应用价值,而且具有很高的学术意义。SHOP型工艺的工业化引起了人们对基于P∩O配位型及其他配位型镍催化剂的广泛的研究兴趣。镍系催化剂具有活性高、选择性好、产品分布可调、反应条件温和等优良性能。本文介绍了镍系催化剂的类型和性能等,并对影响催化性能的因素进行了分析。

Ni/La_2O_3/α-Al_2O_3中的高温脱附氢促进CH_4/CO_2重整反应的初活性

通过H2程序升温脱附实验,在H2还原的Ni/La2O3/-αAl2O3催化剂上可以明显观察到高温脱附氢(高温氢).动力学实验结果表明,随催化剂上高温氢含量的增加,CH4/CO2重整反应的初始活性升高,同时高温氢也可在重整反应过程中原位生成,并使重整反应的活性最终达到稳定.脉冲实验结果表明,随催化剂上高温氢含量的增加,CH4解离后生成的活性中间体CHx物种的x值也增大,进而降低了CHx与CO2反应的活化能,提高了CHx与CO2反应的速率.La2O3助剂的添加提高了Ni/La2O3/-αAl2O3催化剂上逆水气变换反应的速率,并且对CO2的活化也有促进作用.La2O3助剂的加入对于CH4/CO2重整反应的重要作用是使高温氢的数量增多且稳定性提高,有利于保持CHx物种中较高的x值,促进重整反应.

BaTiO_3-BaAl_2O_4-Al_2O_3复合载体的制备、表征及其Ni基催化剂催化CH_4/CO_2重整反应性能

以十六烷基三甲基溴化胺为结构导向剂,采用溶胶-凝胶法制备了BaTiO3-BaAl2O4-Al2O3复合载体,采用X射线衍射、红外光谱、N2吸附-脱附、透射电子显微镜和H2程序升温还原等技术对复合载体进行了表征,并以CH4/CO2重整制合成气为探针反应,考察了不同Ni/BaTiO3-BaAl2O4-Al2O3催化剂的性能.结果表明,BaTiO3-BaAl2O4-Al2O3复合载体具有多孔织构特性和较高的比表面积,BaTiO3和BaAl2O4以晶粒状态分布在复合载体的内外表面,晶粒尺寸在20～50nm的范围,复合载体孔径为10～20nm.复合载体上BaTiO3和BaAl2O4的引入,适度削弱了Ni/BaTiO3-BaAl2O4-Al2O3催化剂中Ni物种与γ-Al2O3间的强相互作用,抑止了NiAl2O4尖晶石的生成;当载体中Ba(Ti)含量为17.33%时,其负载的Ni催化剂上CH4/CO2重整制合成气反应的活性和稳定性最高.

水蒸气浓度对合成气制甲烷Ni/γ-Al_2O_3催化剂稳定性影响

通过改变反应体系中水蒸气浓度,考察了不同水蒸气浓度对γ-Al2O3负载的镍基催化剂上合成气制代用天然气(SNG)的反应活性和稳定性。采用X射线衍射、扫描电镜、N2吸附-脱附等技术对催化剂进行了表征。结果表明,催化剂的稳定时间与反应体系中水蒸气的浓度成反比。影响催化剂稳定性的主要因素可能是在高水蒸气浓度的合成气制SNG的反应条件中,γ-Al2O3的水合反应及其引起的γ-Al2O3相变。