Ni基重整催化剂失活机理研究进展

H₂是一种清洁、绿色的燃料和能源载体。目前工业上应用较为成熟的生产工艺是重整反应制氢。其中,Ni基重整催化剂由于其高储量、高活性和低成本的优点而受到研究人员的广泛关注,但在反应过程中存在易因烧结、积炭和中毒等原因而失活的问题。因此,如何提高Ni基重整催化剂的反应稳定性是一个急需解决的问题。本文介绍了上述三种引起Ni基重整催化剂失活的主要原因,并从调控金属Ni粒子粒径、增强金属-载体相互作用、形成晶格氧或表面氧物种以及Ni粒子纳米结构调控四个方面阐述了近年来在抑制失活并提高Ni基重整催化剂反应性能和稳定性领域所取得的研究进展,并且提出优化反应条件、调变化学组成和调控Ni粒子纳米结构将是提高Ni基催化剂在重整反应过程中的稳定性的有效方法。     

Ni基甲烷二氧化碳重整催化剂研究进展

由于甲烷二氧化碳重整将两种温室气体甲烷和二氧化碳转化为可利用的合成气,因此近二十年以来引起了越来越多研究者的关注。其中,Ni基催化剂由于其较高的活性和较低的成本得到了广泛的研究。本文将甲烷二氧化碳重整Ni基催化剂分为负载型和非负载型两大类分别综述了它们的研究进展。针对反应条件下的Ni基催化剂因积炭和烧结引起的失活问题,本文介绍了引起这两个问题的原因,并概括了抑制失活并提升Ni基催化剂活性和稳定性的5条途经,包括选择性钝化活性金属、增强Ni颗粒分散性、控制催化剂的酸碱性、减小Ni颗粒的尺寸以及提高Ni颗粒稳定性。最后指出,设计和制备颗粒小而且稳定的催化剂是同时解决催化剂积炭和烧结两大问题的关键。     

用于甲烷二氧化碳重整反应的Ni基催化剂的研究进展

对用于甲烷二氧化碳重整反应的Ni基催化剂的研究进展进行了概述,详细分析了Ni金属结构形态、载体、助剂及制备方法等方面对Ni基催化剂活性、稳定性及抗积碳性能的影响。     

二氧化碳重整甲烷过程中催化剂积炭现象的探讨

二氧化碳重整甲烷制合成气的研究已逐渐成为国内外催化界研究的热点，由于二氧化碳和甲烷的分子结构及其反应特点，决定了该体系必然存在严重的积炭问题，本文对近年来在二氧化碳重建甲烷反应中有关积炭方面的研究结果进行了综述，其中包括：形成积炭的原因及抑制积炭的工艺条件选择、催化剂的设计、ＣＯ２和ＣＨ４的活化过程及反应机理等。     

Ni基催化剂在甲烷水蒸气重整中的抗积碳研究

采用等体积浸渍法制备镁铝尖晶石结构载体的Ni基催化剂,通过浸渍水解不同质量分数的（3-氨丙基）三乙氧基硅烷制备具有SiO₂包覆层的Ni基催化剂,并加入La助剂,对比SiO₂包覆层及添加La助剂对催化剂性能的影响。利用XRD、N₂-物理吸附、H₂-TPR、TEM、TG等技术对催化剂进行表征。结果表明,SiO₂包覆层可以有效阻止高温条件下催化剂表面积碳的生成,在温度为750℃、n（H₂O）/n（CH₄）=1.0的严苛条件下,相较未进行包覆处理的催化剂,添加La助剂的10%SiO₂包覆催化剂积碳速率降低90%以上。     

Ni基催化剂上乙酸水蒸汽重整研究

为降低生物质裂解过程中副产物乙酸含量,避免对设备的高腐蚀性,通过湿法浸渍制备Ni基催化剂,在此催化剂上进行乙酸水蒸汽重整反应,考察了原料比例和反应温度对乙酸转化率的影响,结果表明,在乙酸与水体积比为1:12、反应温度为600℃下,获得了100%的乙酸转化率。Mg助剂的加入能够有效提高催化剂的抗积炭性能,在长达600min的寿命实验中活性一直维持在100%乙酸转化率。     

Rh添加剂对Ni基催化剂上CH_4干重整的活性研究

甲烷和二氧化碳是2种主要的温室气体,它们的大量排放导致了全球气候变暖、冰川融化、海平面水位上升等一系列严重的环境问题,但同时这2种气体也是重要的碳氢资源,对世界新能源开发利用有着极大地作用。利用CH-4/CO_2重整制取合成气是同时解决这2种气体排放问题的有效方法。文中主要对Ni基催化剂上CH_4/CO_2重整制取合成气的催化活性进行了研究。采用浸渍法制备了一系列的Ni基催化剂,对催化剂的制备方法、反应条件等的影响进行了一系列的分析探讨,并对催化剂进行了BET,SEM,XRD和TG表征分析。结果表明,活性组分Ni和助剂Rh的最佳负载量(质量分数)分别为10%和0.1%,当反应条件为常压、600℃、空速4 500 h~(-1)及n(CO_2)/n(CH_4)=1时,催化剂质量分数0.1%Rh-10%Ni/γ-Al_2O_3上的CH_4,CO_2的转化率分别可达96.69%和88.57%,合成气比例n(H_2)/n(CO)≈1。     

甲烷与二氧化碳重整制合成气Ni与Co基催化剂的研究进展

综述了助剂、载体与催化剂制备方法对Ni基催化剂、Co基催化剂、Ni-Co基催化剂上甲烷与二氧化碳重整制合成气催化性能的影响,以及甲烷与二氧化碳重整催化反应机理的研究,展望了催化剂未来的发展方向。     

甲烷二氧化碳重整镍基催化剂的研究

采用浸渍法制备不同组成催化剂Ni-M/γ-Al₂O₃（M=Zr、Co、Mg、Nd）,通过固定床反应装置考察不同助剂、助剂含量和反应温度对催化剂活性的影响,并对催化剂进行X射线衍射表征。结果表明,14Ni-5Mg/γ-Al₂O₃的催化活性较好,随着反应温度的升高,甲烷转化率和CO收率均升高,反应温度升至800 ℃时,甲烷转化率达97.54%。采用共沉淀法制备载体、浸渍法制备的催化剂14Ni/MgO-Al₂O₃,在反应温度800 ℃、压力1.013 kPa、n(CO₂)∶n(CH₄)=1.2和催化剂用量0.5 g条件下,CO收率高于14Ni-5Mg/γ-Al₂O₃催化剂,但甲烷转化率略低。     

Catalytic test of supported Ni catalysts with core/shell structure for dry reforming of methane

Supported nickel catalysts with core/shell structures of Ni/Al₂O₃ and Ni/MgO-Al₂O₃ were synthesized under multi-bubble sonoluminescence (MBSL) conditions and tested for dry reforming of methane (DRM) to produce hydrogen and carbon monoxide. A supported Ni catalyst made of 10% Ni loading on Al₂O₃ and MgO-Al₂O₃, which performed best in the steam reforming of methane (97% methane conversion at 750 °C) and in the partial oxidation of methane (96% methane conversion at 800 °C), showed also good performance in DRM and excellent thermal stability for the first 150 h. The supported Ni catalysts Ni/Al₂O₃ and Ni/MgO-Al₂O₃ yielded methane conversions of 92% and 92.5%, respectively and CO₂ conversions of 95.0% and 91.8%, respectively, at a reaction temperature of 800 °C with a molar ratio of CH₄/CO₂ = 1. Those were near thermodynamic equilibrium values.     

Simulation of dry reforming of methane in a conventional downfired reformer

A model for industrial top‐fired dry reforming of methane (DRM) and for combined dry reforming and steam reforming of methane was developed for the first time. The model calculates and gives predictions on the temperature profiles for fuel gas, tube walls, and process gas, as well as the process gas composition profiles over the length of the tubes. Radiative heat transfer is modeled by Hottel Zone method. Material and energy balances are solved numerically using Newton‐Raphson solver. Kinetic models for two different DRM catalysts are applied in the model for comparison. Simulation results show that water–gas shift reaction is important in DRM and addition of steam in the feed of process gas is beneficial for industrial production. © 2016 American Institute of Chemical Engineers AIChE J, 63: 2060–2071, 2017     

The effects of stoichiometry on the properties of exsolved Ni-Fe alloy nanoparticles for dry methane reforming

The dry reforming of methane has received notable attention as a chemical process to convert natural gas into value-added chemicals and fuels. Ni-based exsolution catalysts using perovskite oxides supports have been used for their attractive sinter-resistance and coke-resistance properties. The perovskite oxide in itself has unique defect chemistry that can be used to manipulate and control the properties of the catalyst nanoparticles exsolved on the surface, therefore influencing both the nanoparticle and support characteristics. In this study, the La:Fe ratio of Ni-doped LaFeO₃ was used to manipulate and control the properties of exsolved Ni-Fe alloy nanoparticles. The Ni-Fe nanoparticles consisted of different sizes ranging from 10 to 380 nm. Temperature programmed surface reaction studies along with materials characterization with SEM, STEM-HAADF, XRD, and BET showed that the Ni-Fe nanoparticles from different solid precursors have the same active sites for methane activation but differ in performance and stability because of size effects, metal-support strength, composition and support basicity. A mechanism is proposed to decipher the merits of the Ni-Fe nanoparticles with the best activity, selectivity, and stability in this study.     

Nano‐engineered nickel catalysts supported on 4‐channel α‐Al2O3 hollow fibers for dry reforming of methane

A nickel (Ni) nanoparticle catalyst, supported on 4‐channel α‐Al₂O₃ hollow fibers, was synthesized by atomic layer deposition (ALD). Highly dispersed Ni nanoparticles were successfully deposited on the outside surfaces and the inside porous structures of hollow fibers. The catalyst was employed to catalyze the dry reforming of methane (DRM) reaction and showed a methane reforming rate of 2040 Lh^?1gNi^?1 at 800°C. NiAl₂O₄ spinel was formed when Ni nanoparticles were deposited on alpha‐alumina substrates by ALD, which enhanced the Ni‐support interaction. Different cycles (two, five, and ten) of Al₂O₃ ALD films were applied on the Ni/hollow fiber catalysts to further improve the interaction between the Ni nanoparticles and the hollow fiber support. Both the catalyst activity and stability were improved with the deposition of Al₂O₃ ALD films. Among the Al₂O₃ ALD coated catalysts, the catalyst with five cycles of Al₂O₃ ALD showed the best performance. © 2018 American Institute of Chemical Engineers AIChE J, 64: 2625–2631, 2018     

MCM-41 supported PdNi catalysts for dry reforming of methane

A series of bimetallic PdNi catalysts supported on mesoporous MCM-41 with different Ni content (Ni/Si ratio of 0.2–0.4) was synthesized. The effect of Pd addition to Ni-containing catalysts as well as the effect of the Ni content on the surface and catalytic properties of the catalysts was studied. The samples were characterized using various techniques, such as energy-dispersive X-ray spectroscopy, N₂ adsorption–desorption isotherms, X-ray diffraction, thermogravimetric and differential analyses, X-ray photoelectron spectroscopy, high resolution transmission electron microscopy and temperature-programmed reduction. Reforming of methane with carbon dioxide was used as a test reaction. The results indicated that the addition of a small amount of Pd (0.5%) to Ni-containing catalysts leads to formation of small nano-sized, easy reducible NiO particles. Agglomeration of NiO as well as of metallic nickel phase over PdNi samples increased with increasing the Ni content. Formation of filamentous carbon over surface of spent monometallic Ni and bimetallic PdNi catalyst was observed. In spite of filamentous carbon deposition, the catalytic activity and stability of bimetallic PdNi catalysts are higher than those of monometallic Ni one. Within bimetallic system, the PdNi catalyst with Ni/Si ratio of 0.3 revealed the best performance and stability caused by presence of small nickel particles well dispersed on the catalyst surface.     

C-H-O三元热力学图在甲烷重整积炭研究中的研究进展

从热力学的角度对甲烷重整过程中的积炭现象进行了综述研究,分析了C-H-O三元素组分的积炭三角图以及不同甲烷重整形式的非积炭区域,包括了SMR、CDR、POM、TRM以及甲烷在燃料电池电化学阳极室中的重整过程。最后提出了热力学视角下缓解积炭的措施是联合重整能有效地减少积炭,而采用阳极注氧能够改善甲烷燃料电池的积炭现象。     

Dry reforming of methane to synthesis gas over supported molybdenum carbide catalysts

The dry reforming of methane at elevated pressure over supported molybdenum carbide catalysts, prepared from oxide precursors using ethane TPR, has been studied. The relative stability of the catalysts is Mo₂C/Al₂O₃>Mo₂C/ZrO₂>Mo₂C/SiO₂>Mo₂C/TiO₂, and calcination of the oxide precursor for short periods was found to be beneficial to the catalyst stability. Although the support appears to play no beneficial role in the methane dry reforming reaction, the alumina-supported material was stable for long periods of time; this may be important for the production of pelletised industrial catalysts. The evidence suggests that the differences in the stabilities may be due to interaction at the precursor stage between MoO₃ and the support, while catalyst deactivation is due to oxidation of the carbide to MoO₂, which is inactive for methane dry reforming.