Li助剂对Co/AC催化剂上CO加氢制直链混合伯醇反应性能的影响

采用CO加氢反应、X射线衍射、程序升温还原和CO程序升温脱附等技术研究了Li助剂对活性炭负载的Co催化剂(Co/AC)上CO加氢反应性能的影响.结果表明,Li的添加抑制了气态烃的生成,提高了C5+和直链混合伯醇的选择性,但催化剂活性下降.这可能源于Li的加入抑制了Co2+物种的还原,降低了反应速控步骤—强吸附CO的解离...     

不同MgO担体对Ba-Ru/MgO氨合成催化剂物化性质和反应性能的影响

采用不同沉淀剂制备了MgO材料,以其为载体制备了Ba-Ru/MgO氨合成催化剂,考察了沉淀剂种类和BaO助剂对其氨合成性能的影响.通过X射线衍射(XRD)、N2物理吸附、X射线荧光光谱(XRF)、透射电镜(TEM)、H2程序升温还原(H2-TPR)、CO2程序升温脱附(CO2-TPD)、H2程序升温脱附(H2-TPD)和N2程序升温脱附(N2-TPD)表征手段,对不同沉淀剂影响Ba-Ru/MgO催化剂氨合成性能的原因进行了探索.结果表明:采用(NH4)2CO3作沉淀剂制备的Ba-Ru/MgO催化剂表面Ru物种易于在低温下还原,催化剂表面在低温区具有较多数量的弱碱性吸附位,在450℃、5.0 MPa和5 000 h-1条件下,由(NH4)2CO3做沉淀剂制备的Ba-Ru/MgO催化剂活性最高,出口氨浓度为3.74%.BaO助剂的加入大大减少了Ba-Ru/MgO催化剂表面吸附氢的数量,增大表面脱附氮的数量,从而易于N2解离吸附,提高氨合成反应速率.     

钴和钾对Pt/γ-Al2O3上CO选择性氧化的助催化作用

 添加Co或/和K助催化剂可在不同程度上改善Pt/γ-Al2O3催化剂对富氢气氛下CO选择性氧化的性能. 利用H2-TPR,CO-TPD和FT-IR等表征手段,探讨了不同助催化剂的作用机理. 结果表明,Co/Pt/γ-Al2O3能显著降低富氢气氛下CO选择性氧化的温度,主要原因是Co与Pt的相互作用使Pt的电子性能发生了改变,从而削弱了Pt对CO的吸附,使催化剂表面CO的线式吸附消失; Co的添加还促进了易分解的碳酸氢盐物种的生成,同时未完全还原的CoOx物种可提供活性氧促进CO的转化. 助催化剂K一方面促进了Pt向CO反馈电子,从而活化吸附的CO,提高了催化剂的低温活性;另一方面促进了难分解的甲酸盐物种的生成,从而抑制了部分活性位,需要更高的反应温度,而较高温度下会发生氢气氧化反应的竞争,使CO选择性氧化反应的活性和选择性受到影响. 同时添加K和Co的催化剂中,K可促进CoOx的还原,使Co与Pt的相互作用变弱,即减弱了Co对Pt的助催化作用, 因此虽然其选择性有所改善,但活性介于单独添加Co或K的催化剂之间.     

Ni/La2O3/α-Al2O3中的高温脱附氢促进CH4/CO2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/α-Al2O3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/α-Al2O3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.     

钴基费-托合成催化剂上CO、H_2的吸附行为

采用程序升温脱附及FT-IR技术考察了CO、H2在钴基催化剂上的吸附行为.H2-TPD表明,Co/SiO2催化剂有两类脱附氢,引入锆助剂后,低温脱附氢量明显增加,高温吸附氢量下降.CO-TPD及吸附态CO的红外光谱表明锆助剂使CO在钴催化剂上的吸附强度减弱,但其吸附量增大.钴基催化剂的费-托合成反应性能可以用吸附态物种的变化来解释.     

CeO2和Co3O4助剂对镍基催化剂上CH4积碳和CO2消碳性能的影响

采用脉冲微反技术研究了添加CeO2和Co3O4助剂对镍基催化剂上CH4积碳和CO2消碳性能的影响,并用BET,TGA,XPS及CO2-TPSR等技术对催化剂进行了表征. 结果表明,添加CeO2可以提高活性原子Ni0中d电子的密度; Ni0原子中d电子密度的增加在一定程度上抑制了CH4分子中C-H键σ电子向d轨道的迁移,降低了CH4裂解积碳性能; 同时加强了Ni0原子d轨道向CO2空反键π轨道的电子迁移,促进了CO2分子的活化,提高了CO2的消碳活性. 助剂Co3O4的添加则促进CH4的裂解积碳,抑制了CO2的消碳.分析表明,活性金属与半导体助剂之间存在的金属-半导体相互作用是影响这种机制的主要因素.     

Co/SiO2催化剂催化费托合成中CeO2助剂的作用

 在Co/SiO2催化剂中加入少量CeO2助剂, 能够提高其催化费托(FT)反应的活性和液态烃(Ｃ5+)的选择性,特别是可以生成优质的高附加值柴油及润滑油基础油(C12+), 但助剂CeO2对Co/SiO2催化剂的作用目前仍存在争议. 本文利用X射线衍射、程序升温还原、程序升温脱附、程序升温表面反应、 X射线光电子能谱、扫描电镜和同位素脉冲反应结合H-D同位素交换等方法对催化剂进行了表征,并采用微反评价考察了催化剂的催化性能. 表征结果表明,少量CeO2助剂的添加提高了活性组分Co在催化剂表面的分散度,降低了催化剂表面Co的晶粒度,使催化剂对CO和H2的吸附性能发生了改变. 同位素脉冲反应结合H-D交换实验表明, CeO2的添加减弱了Co的金属性,提高了其吸附解离氢的能力和CO吸附量,增大了催化剂表面活性碳物种的浓度和聚合趋势,使FT合成的碳链增长几率增大至0.90, 产物中液态烃选择性和重质烃含量明显增加,说明CeO2的加入有利于生成高附加值的柴油和润滑油基础油.     

Effects of Li Promoter on the Performance of Co/AC Catalysts for CO Hydrogenation to Mixed Linear a-Alcohols

采用CO加氢反应、X射线衍射、程序升温还原和CO程序升温脱附等技术研究了Li助剂对活性炭负载的Co催化剂(Co/AC)上CO加氢反应性能的影响.结果表明,Li的添加抑制了气态烃的生成,提高了C5+和直链混合伯醇的选择性,但催化剂活性下降.这可能源于Li的加入抑制了Co2+物种的还原,降低了反应速控步骤—强吸附CO的解离能力.另外,Li也促进了Co2C物种的生成,使得产物中混合醇的比例增加.     

Pt,Ru和Pd助剂对F-T合成中Co/γ-Al2O3催化剂性能的影响

 采用浸渍法制备了添加贵金属Pt,Ru和Pd助剂的Co/γ-Al2O3催化剂,并考察了它们在F-T合成反应中的催化性能. 结果表明,添加贵金属助剂可以显著提高Co/γ-Al2O3催化剂的催化活性. XRD和TPR表征结果表明,贵金属助剂不但可以使催化剂的金属分散度增加,而且可以通过氢溢流促进催化剂表面活性相的Co3O4以及与载体Al2O3有相互作用的非活性相钴氧化物物种的还原,从而改善催化剂的还原性能. TPSR结果进一步表明,添加贵金属助剂后催化剂对CO的吸附解离能力增强,从而使吸附态CO的加氢活性提高.     

K改性的Pt/Al2O3催化剂上CO氧化反应：反应动力学和红外光谱研究

CO氧化不仅具有重要的实用价值,而且在基础研究中被用于考察反应机理及催化剂结构敏感性等一些重要问题,因此,该反应在催化领域中具有重要意义. Pt基催化剂被广泛应用于CO氧化反应.其催化活性取决于催化剂的制备方法.其中,碱金属如Na、K等助剂的添加可有效促进催化活性,红外光谱证据表明,其促进作用在于碱金属的添加可降低CO与表面Pt原子的相互作用.尽管如此,催化剂上反应动力学证据却十分缺乏.反应动力学的研究可以提供一些本证反应信息如反应基元步骤、反应速率表达式以及反应机理等.通过对比不同催化剂之间的反应动力学行为,可以进一步解释碱金属对催化剂结构以及反应行为的影响.因此在本工作中,我们制备了一系列以K为助剂的Pt/Al2O3催化剂,并进行了CO氧化的反应动力学研究,考察了助剂对CO反应级数和反应活化能的影响.结合原位红外光谱表征,进一步揭示了助剂在反应中的作用.通过对比不同Pt和K含量的催化剂上CO氧化反应活性,我们发现, K的添加能促进反应活性,且随着催化剂中K含量的增加,促进程度越明显.例如,0.42K-2Pt/Al2O3上T50温度比对应的2Pt/Al2O3降低了30oC.不同催化剂上CO氧化的反应动力学实验表明,反应速率随着CO的分压的增加而降低;但随着O2分压的增加而增大.幂函数反应速率表达式推导得到的反应级数发现,对于含K的催化剂其CO的反应级数(约为–0.2)明显比不含K的催化剂(约为–0.5)中高,说明K的添加减弱了CO与表面Pt原子之间的吸附能力.但对O2的反应级数影响较小.例如：在0.42K-2.0Pt/Al2O3上反应速率表达式为r =6.55′10–7pco–0.22po20.63;而在2.0Pt/Al2O3上为r =2.56′10–7pco–0.53po20.70.表观反应活化能的计算表明,含K的催化剂上表观反应活化能较低,进一步说明K的添加有利于反应进行.根据反应速率表达式,我们进行了基元步骤的推导,并计算了反应动力学参数.结果发现,与不含K的催化剂相比,含K的催化剂中本征反应速率常数明显增加,而CO吸附平衡常数降低了一半,表明K的存在使CO在Pt表面上的覆盖度降低.我们还通过原位红外光谱对比了催化剂上CO吸附行为的差异.数据表明,与不含K的催化剂相比, K的添加一方面降低了CO在催化剂表面的吸附量(峰面积变小);另一方面显著降低了CO在Pt表面上的脱附温度,说明两者之间的相互作用力减弱.综上所述,通过反应动力学和红外光谱实验,我们认为K助剂与表面Pt原子相互作用后生成了较为稳定的Pt–O–K物种.尽管该物种的具体结构目前还不明确,但我们的实验证据表明,该物种的存在可以有效减弱CO与表面Pt原子之间的相互作用,降低CO的表面覆盖度并有利于O2在Pt表面的竞争吸附,从而降低了表面吸附的CO与O2之间反应的能垒,促进了反应性能.     

Studies on Carbon Deposition on Hexaaluminate LaNiAl11O19 Catalysts during CO2 Reforming of Methane

The amount of carbon deposited on hexaaluminate LaNiAl₁₁O₁₉ catalyst in CH₄ decomposition and CO₂ reforming of methane was determined by means of thermogravimetric analysis (TGA). The properties of carbon formed on the catalysts were characterized by X-ray photoelectron spectroscopy (XPS), temperature-programmed CO₂ reaction (TPR-CO₂), and temperature-programmed oxidation (TPO) techniques. The experimental results showed that hexaaluminate LaNiAl₁₁O₁₉ catalyst possessed high resistance to carbon deposition in CO₂ reforming of methane to synthesis gas at high temperatures, and CO₂ played an important role in eliminating carbon during the reaction. At least two forms of the deposited carbon, graphite and carbide, were produced during methane reforming with CO₂.     

CO2预处理操作条件对Ni-Co双金属催化剂性能与结构的影响

与传统H₂预处理方法相比,新型H₂+CO₂预处理方法（HCD）能显著提升Ni-Co双金属催化剂的沼气重整活性及抗积碳性能. 考察了HCD预处理操作条件对催化剂性能与结构的影响. 较好的HCD预处理操作条件是在催化剂经H₂处理之后,再用175-200 mL·min^-1的原料气CH₄/CO₂（比例为0：10）在780-800 ℃下还原0.5-1h. 在优化预处理操作条件下对催化剂进行了511 h的耐久性考察,并运用X射线衍射（XRD）、热重-差示扫描量热（TG-DSC）、透射电子显微镜（TEM）等手段对耐久性测试后的催化剂进行了表征. 在511 h 的稳定性实验内,CH₄、CO₂转化率,H₂、CO选择性及H₂/CO体积比分别高达96%、97%,98%、99%及0.98. 催化剂在测试期间的平均积碳速率仅为0.2 mg·g^-1·h^-1. 在该预处理操作参数下,催化剂拥有最好的综合性能和良好的耐久性.     

Carbon dioxide reforming of methane over Ni/Mo/SBA-15-La2O3 catalyst: Its characterization and catalytic performance

The Ni/Mo/SBA-15 catalyst was modified by La2O3 in order to improve its thermal stability and carbon deposition resistance during the CO2 reforming of methane to syngas. The catalytic performance, thermal stability, structure, dispersion of nickel and carbon deposition of the modified and unmodified catalysts were comparatively investigated by many characterization techniques such as N2 adsorption, H2-TPR, CO2-TPD, XRD, FT-IR and SEM. It was found that the major role of La2O3 additive was to improve the pore structure and inhibit carbon deposition on the catalyst surface. The La2O3 modified Ni/Mo/SBA-15 catalyst possessed a mesoporous structure and high surface area. The high surface area of the La2O3 modified catalysts resulted in strong interaction between Ni and Mo-La, which improved the dispersion of Ni, and retarded the sintering of Ni during the CO2 reforming process. The reaction evaluation results also showed that the La2O3 modified Ni/Mo/SBA-15 catalysts exhibited high stability.     

Ni/MgO catalyst prepared using atmospheric high-frequency discharge plasma for CO2 reforming of methane

A new type of Ni/MgO catalyst was prepared using atmospheric high-frequency discharge cold plasma. The influences of conventional method, plasma method, and plasma plus calcination method on the catalytic activity were studied and the CO2 reforming of methane was chosen as the probe reaction. The catalysts were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), X-ray photoelectron spectroscopy, and CO2 temperature-programmed surface reaction techniques. The results suggested that the nickel-based catalyst prepared by plasma plus calcination method possessed a smaller particle size and a higher dispersion of active component, better low-temperature activity and enhanced anti-coking ability. The conversion of CO2 and CH4 was 90.70% and 89.37%, respectively, and the reaction lasted for 36 h without obvious deactivation under 101.325 kPa and 750°C with CO2/CH4 = 1/1.     

Methane Activation by Platinum: Critical Role of Edge and Corner Sites of Metal Nanoparticles

Complete dehydrogenation of methane is studied on model Pt catalysts by means of state‐of‐the‐art DFT methods and by a combination of supersonic molecular beams with high‐resolution photoelectron spectroscopy. The DFT results predict that intermediate species like CH₃ and CH₂ are specially stabilized at sites located at particles edges and corners by an amount of 50–80 kJ mol^?1. This stabilization is caused by an enhanced activity of low‐coordinated sites accompanied by their special flexibility to accommodate adsorbates. The kinetics of the complete dehydrogenation of methane is substantially modified according to the reaction energy profiles when switching from Pt(111) extended surfaces to Pt nanoparticles. The CH₃ and CH₂ formation steps are endothermic on Pt(111) but markedly exothermic on Pt₇₉. An important decrease of the reaction barriers is observed in the latter case with values of approximately 60 kJ mol^?1 for first C? H bond scission and 40 kJ mol^?1 for methyl decomposition. DFT predictions are experimentally confirmed by methane decomposition on Pt nanoparticles supported on an ordered CeO₂ film on Cu(111). It is shown that CH₃ generated on the Pt nanoparticles undergoes spontaneous dehydrogenation at 100 K. This is in sharp contrast to previous results on Pt single‐crystal surfaces in which CH₃ was stable up to much higher temperatures. This result underlines the critical role of particle edge sites in methane activation and dehydrogenation.     

镍前驱体对非负载型镍催化剂上甲烷分解活性的影响

 分别以硝酸镍和乙酸镍为前驱体, 采用沉淀法制备了非负载型 Ni 催化剂, 运用 X 射线衍射、H2-程序升温还原及 CH4 程序升温表面反应对催化剂进行了表征, 并考察了 Ni 催化剂上 CH4 分解反应活性. 结果表明, 以乙酸镍为前驱体制得的 NiO 样品粒子尺寸较小, 较易被还原, 还原后得到的催化剂催化 CH4 分解活性和稳定性较高; 而以硝酸镍为前驱体制得的 NiO 样品粒子尺寸较大, 较难被还原, 还原后催化剂上 CH4 分解活性和稳定性较低. 制备过程中乙酸镍与溶剂乙二醇所形成的配合物是获得尺寸较小 NiO 样品的关键.     

Dry Reforming of Methane on a Highly‐Active Ni‐CeO2 Catalyst: Effects of Metal‐Support Interactions on C−H Bond Breaking

Ni‐CeO₂ is a highly efficient, stable and non‐expensive catalyst for methane dry reforming at relative low temperatures (700 K). The active phase of the catalyst consists of small nanoparticles of nickel dispersed on partially reduced ceria. Experiments of ambient pressure XPS indicate that methane dissociates on Ni/CeO₂ at temperatures as low as 300 K, generating CH_x and CO_x species on the surface of the catalyst. Strong metal–support interactions activate Ni for the dissociation of methane. The results of density‐functional calculations show a drop in the effective barrier for methane activation from 0.9 eV on Ni(111) to only 0.15 eV on Ni/CeO_2?x(111). At 700 K, under methane dry reforming conditions, no signals for adsorbed CH_x or C species are detected in the C 1s XPS region. The reforming of methane proceeds in a clean and efficient way.     

CO2 reforming of methane over zirconia-supported nickel catalysts, I. Catalytic specificity

CO₂ reforming of methane is performed over zirconia-supported nickel catalysts. The catalysts show high activity toward CH₄ and CO₂ conversions. Over the high Ni loading catalyst, long-term performances without significant deactivations have been achieved at 1023 K for 30 h and 1123 K for 20 h, respectively. The effects of reduction and calcination temperatures on the catalytic activities are also examined.     

The Order of Product Formation in the Partial Oxidation of Methane to Syngas

The partial oxidation of methane to syngas is studied in the presence of Pt- and Ni-containing catalysts. The process kinetics does not provide unequivocal information on the order of formation of products (including carbon oxides) when either methane–oxygen or methane–oxygen–CO₂ mixtures are used. Experiments with ¹³C-labeled carbon dioxide added show the difference in the behavior of the catalysts. In the presence of Pt/ZrO₂, there is no noticeable transfer of the isotopic label to the CO molecules. On the nickel catalyst, ¹³CO is formed in substantial amounts, which can probably be explained by the redox reaction of ¹³CO₂ with metallic nickel under oxygen-free conditions behind the zone of the main reaction of methane oxidation.     

Computational fluid dynamics study of the dry reforming of methane over Ni/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst in a membrane reactor. Coke deposition

This work investigates the dry reforming of CH₄ as an important process for the conversion of greenhouse gases to synthesis gas. The mixture of methane and CO₂ is readily available in the greenhouse gas which makes realization of dry reforming of methane process more convenient. The paper is an attempt to numerically analyse by computational fluid dynamics (CFD) the coking and gasification mechanisms in the lab-scale membrane module with a fixed-bed supported nickel catalyst (Ni/Al₂O₃). The concentrations and molar fluxes obtained by the simulation are compared with the experimental profiles to validate the CFD model. It was found that working in a catalytic fixed-bed membrane reactor, in the case of the dry reforming of methane and under specific conditions, was not critical, from the point of view of catalyst deactivation.