助剂MgO、CaO对甲烷水蒸气重整Ni/γ-Al_2O_3催化性能的影响

采用固定床装置,考察了以共浸方式引入的助剂MgO、CaO对Ni/γ-Al2O3催化剂在甲烷水蒸气催化重整中的催化反应性能的影响。结果表明,在H2O/CH4/N2的摩尔比为2.86/1/3.28,GHSV为1 800 h-1,反应温度为700℃下,催化剂Ni-CaO/Al2O3催化性能最好;反应初期甲烷转化率可达到96.95%、CO选择性可达68.93%、H2收率可达73.58%。XRD和H2-TPR结果表明,CaO的存在使催化剂中的活性NiO组分增多,还原性和分散性能较好。利用热分析技术对积炭进行考察发现反应10 h后的Ni-CaO/Al2O3催化剂上并未出现导致催化剂失活的炭物种。     

等离子体引入方式对强化制备二氧化碳重整甲烷反应的Ni/γ-Al2O3催化剂的影响

采用等离子体技术强化制备了Ni/γ-Al2O3催化剂, 以CO2重整CH4为模型反应考察了等离子体引入方式对催化剂性能的影响, 并采用H2-TPR, BET, CO2-TPD, XRD, CO2-TPSR, TGA及XPS技术对催化剂进行了表征. 研究结果表明, 与常规焙烧的催化剂相比, 在氢气还原过程前引入氮气等离子体处理能有效提高催化剂的低温反应活性. N2气等离子体处理使前驱体中的硝酸盐能在温和条件下分解, 并使催化剂具有较强的还原能力和较大的比表面积. 先进行N2气等离子体处理再进行H2气还原的催化剂, 其活性组分的分散度显著提高, 对CO2的吸附量也明显增加, 并且反应后催化剂上的积炭量比常规催化剂上的显著降低, 形成比较单一的碳物种.     

基于改性Ni/γ-Al_2O_3催化剂的电催化甲烷水蒸气重整的研究

提出了电催化作用下甲烷水蒸气催化重整的新工艺。基于工业常规Ni基催化剂,采用等体积浸渍法,以Ni为活性组分,γ-Al_2O_3为载体,MgO、CaO为助剂,制备了Ni/γ-Al_2O_3、Ni-MgO/γ-Al_2O_3和Ni-CaO/γ-Al_2O_3催化剂,考察了电流强度、重整温度、水蒸气与甲烷的物质的量比(水碳比,S/C)对不同催化剂的CH_4转化率、H_2产率、CO选择性和催化剂稳定性的影响。结果表明,电催化工艺有着良好的普适性,电流的引入能够提升CH_4转化率、增加H_2产率,尤其在低温下电流的促进作用显著。在三种催化剂中,Ni-CaO/γ-Al_2O_3催化效果最佳,在电流为4.5 A、S/C为3、重整温度为700℃时,CH_4转化率就高达95%以上。稳定性测试表明,电流的通入还能显著提高催化剂的稳定性,延缓催化剂的积炭失活。通过对催化剂的分析表征,发现电流的通入提升了催化剂中NiO的还原程度,同时抑制了反应过程中NiC_x向石墨炭的转化,从而可延缓催化剂因积炭覆盖反应活性位点而造成的失活。     

不同形貌Ni/γ-Al2O3催化剂催化CO甲烷化反应的研究

采用沉淀法分别以乙二醇、水、乙二醇-聚乙二醇600为修饰剂,制备了形貌分别为棒状（a-NiO）、粒状（b-NiO）和片状（c-NiO）结构的NiO催化剂,然后和γ-Al₂O₃通过研混法制得NiO/γ-Al₂O₃催化剂。采用XRD、TEM及H₂-TPR等技术手段对催化剂进行了表征。TEM观察NiO的形貌分别为棒状、粒状和片状。H₂-TPR结果表明,NiO/γ-Al₂O₃催化剂的氧化中心数量顺序为b-NiO/γ-Al₂O₃＜a-NiO/γ-Al₂O₃＜c-NiO/γ-Al₂O₃。XRD结果表明,NiO/γ-Al₂O₃催化剂还原后的Ni晶粒尺寸大小为b-Ni＞a-Ni＞c-Ni。在连续流动固定床反应装置上考察了Ni/γ-Al₂O₃对CO甲烷化反应的催化活性,研究了混合方法和形貌对CO甲烷化反应的影响。结果表明,研混法制得催化剂的活性及稳定性较好。催化剂形貌对CO甲烷化反应的催化活性顺序为c-Ni/γ-Al₂O₃＞a-Ni/γ-Al₂O₃＞b-Ni/γ-Al₂O₃,常压、593K和2500h^-1反应条件下,w_Ni为15% c-Ni/γ-Al₂O₃催化CO合成CH₄选择性及CO转化率分别达90.80%和99.63%。     

制备方法对甲烷干重整催化剂Ni/La2O3/Al2O3结构及性能的影响

采用浸渍法及蒸发法制备了Ni/La₂O₃/Al₂O₃催化剂,考察了制备方法对其结构及甲烷干重整催化性能的影响。通过XRD、H₂ TPR、BET、TEM、TG-DSC等方法对催化剂进行了表征。结果表明,浸渍法制备的催化剂具有较好的Ni分散性、更均匀的粒径分布,较大的比表面积及更优的孔结构,从而具有更好的Ni抗烧结能力及抗积炭性。浸渍法制备的催化剂平均积炭速率很低,约为0.6737mg/(g_cat·h),相当于蒸发法制备催化剂的21%。活性测试结果表明,浸渍法制备的催化剂上CH₄、CO₂转化率及H₂、CO选择性比蒸发法制备的催化剂分别高约5%、10%及4%、3%,具有更好的稳定性。     

镍负载量对Ni/MgO(111)催化甲烷二氧化碳重整反应性能影响

研究了MgO(111)负载镍基催化剂催化甲烷二氧化碳重整反应性能,针对镍负载量对反应活性和稳定性的影响进行了探讨。结果表明,随着镍负载量从2%增加到10%,催化剂的活性和稳定性均有所提高,但是当镍负载量进一步增加到20%时,催化剂的活性和稳定性略有下降。利用透射电子显微镜、X射线衍射和H₂吸附脱附等手段对催化剂结构进行了表征,利用热重分析、拉曼光谱和透射电镜等手段对反应后回收的催化剂进行了表征。研究发现,随着镍负载量的增大,活性金属镍的颗粒粒径呈现增长趋势,并且在反应过程中显示出不同的失活方式。2%Ni/MgO(111)催化剂的失活原因主要以Ni粒子的氧化为主,而负载量大于2%的Ni/MgO(111)催化剂的失活原因则是以积炭为主。     

加压下Ni/MgO催化剂催化CO2重整CH4反应的特性

 以在流动N2中热处理的Mg(OH)2醇凝胶制得的纳米氧化镁(MgO-AN)为载体,制备了Ni/MgO-AN催化剂. 这种催化剂在常压下的CO2重整CH4反应中表现出了高活性和稳定性,而在加压反应中的催化活性随着反应压力的升高而降低,并呈现出自稳定特性. 采用TG,XRD和TPH技术对催化剂进行了表征. 结果表明,常压反应中催化剂表面的积炭量很少,而在加压反应中催化剂表面有明显的积炭,且积炭量随着反应的进行逐渐增加,并在12 h左右达到一个稳定值. 催化剂的活性组分金属Ni在常压CO2重整CH4反应中不发生烧结长大,而在加压反应中发生明显的烧结. 常压反应中催化剂表面只形成一种积炭物种,而在加压反应中形成两种积炭物种. 因此,Ni/MgO-AN在加压反应中的催化行为与常压反应中的有明显区别.     

等离子体处理制备对甲烷重整Ni基催化剂抗积炭性能的改进

对于甲烷重整反应,Ni基催化剂具有与贵金属催化剂相当的活性,但其易于积炭失活.本文总结了辉光放电等离子体处理制备CO2甲烷重整Ni催化剂以提高催化剂抗积炭性能的研究进展.比较表明,辉光放电等离子体处理制备的Ni催化剂,Ni颗粒较小,分散性更好,密集平面增加,且Ni活性组分与载体相互作用加强.这些变化导致Ni催化剂抗积炭性能改善.     

SiO2和Al2O3负载的Ni基催化剂在甲烷干重整中的催化性能差异

CH₄与CO₂干重整反应对于环境保护和天然气资源的合理利用具有重要意义。SiO₂和Al₂O₃是适用于甲烷干重整反应的两种典型的催化剂载体。为了阐明这两种载体对催化剂性能的影响,本研究采用等体积浸渍法制备了Ni/Al₂O₃和Ni/SiO₂催化剂,并利用BET、TEM、H₂-TPR、XRD、TG和Raman等技术对还原和反应后的催化剂进行了表征。结果表明,由于载体的性质不同,Ni基催化剂在甲烷干重整中的催化性能也不同。Ni/SiO₂催化剂的初始活性较高,但由于其金属-载体相互作用较弱,催化稳定性较差,在800℃下反应15h其催化活性急剧下降;较弱的金属-载体相互作用使得Ni/SiO₂催化剂上的Ni颗粒较大,有利于积炭前驱物种的生成,导致催化剂快速失活。而对于Ni/Al₂O₃催化剂,金属-载体相互作用较强,Ni颗粒较小,但由于Ni与Al₂O₃生成了NiAl_xO_y物种,有效活性位减少,其催化活性相对较低,但催化稳定性较好,干重整反应进行50h其活性保持稳定;Ni与Al₂O₃之间较强的相互作用有利于形成小且稳定的Ni粒子,能减少积炭,因而具有优异的催化稳定性。     

Ni/ZrO2催化剂上甲烷水蒸气重整反应的研究

研究了Ni/ZrO2催化剂对甲烷水蒸气重整制合成气的反应性能。考察了催化剂的还原温度、载体焙烧温度以及反应温度、原料配比和空速等对催化剂性能的影响。利用XRD、TEM、XPS等手段对催化剂的织构形貌进行了表征。研究表明，Ni/ZrO2催化剂用于甲烷水蒸气重整制合成气不仅具有较高的活性，也具有较好的稳定性。水蒸气比增加，CH4转化率增大、CO选择性下降。CH4转化率及CO选择性均随空速增大而下降。使用10%Ni/ZrO2催化剂，在650 ℃、空速1.984×104 h－1、原料气配比H2O∶CH4∶N2=2∶1∶2.67的条件下，获得CH4转化率85%、CO选择性70%的结果。     

Influence of MgO in the CO2 – steam reforming of methane to syngas by NiO/MgO/ α-Al2O3 catalyst

Simultaneous steam and CO₂ reforming of methane to syngas (H₂and CO) over NiO/MgO/a-Al₂O₃ catalyst have been investigated at different MgO wt.%. The catalyst has been characterized by temperature-programmed reduction and XRD techniques. Addition of MgO reduced the carbon deposition and energy consumption. The stability and less coking on MgO-promoted catalysts are attributed to the lewis basicity of MgO.     

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.     

CaO/MgO负载的钙钛矿型氧化物用于甲烷化学链蒸汽重整

甲烷化学链蒸汽重整(Chemical-looping steam methane reforming,CL-SMR)是基于化学链燃烧的概念而提出的一种新颖的技术。在重整反应器中,甲烷与载氧体中的晶格氧发生部分氧化反应生成合成气(H₂/CO物质的量比为2.0),还原后的载氧体进入到水蒸气反应器中,与水蒸气反应恢复晶格氧的同时生成H₂。以钙钛矿型氧化物LaFeO₃为载氧体用于甲烷化学链蒸气重整过程,同时通过碱金属CaO和MgO对LaFeO₃进行负载,以增大载氧体的比表面积、热稳定性和抗积炭能力。通过X射线衍射(XRD)、H₂程序升温还原(H₂-TPR)、BET比表面积分析(BET)和X光电子能谱(XPS)对载氧体进行表征。结果表明,三种载氧体均表现出较高的反应活性和合成气选择性,循环后仍能保持钙钛矿的结构。从反应性能、选择性和抗积炭能力等方面综合考虑,LaFeO₃-CaO的效果最好,五次循环后具有很好的再生性。     

Effect of MgO promoter on Ni-based SBA-15 catalysts for combined steam and carbon dioxide reforming of methane

A series of Ni/SBA-15 catalysts with Ni contents ranging from 5 wt% to 15 wt%, as well as another series of 10%Ni/MgO/SBA-15 catalysts, in which the range of the MgO content was from 1 wt% to 7 wt%, were prepared, and their catalytic performances for the reaction of combined steam and carbon dioxide reforming of methane were investigated in a continuous flow microreactor. The structures of the catalysts were characterized using the XRD, H2-TPR and CO2-TPD techniques. The results indicated that the CO selectivity for this reaction was very close to 100%, and the H2/CO ratio of the product gas could be controlled by changing the H2O/CO2 molar ratio of the feed gas. The simultaneous and plentiful existing of steam and CO2 had a significant influence on the catalytic performance of the 10%Ni/SBA-15 catalyst without modification. After reacting at 850 °C for 120 h over this catalyst, the CH4 conversion dropped from 98% to 85%, and the CO2 conversion decreased from 86% to 53%. However, the 10%Ni/3%MgO/SBA-15 catalyst exhibited a much better catalytic performance, and after reacting for 620 h, the CO2 conversion over this catalyst dropped from 92% to around 77%, while the CH4 conversion was not decreased. Oxidation of the Ni0 species as well as carbon deposition during the reaction were the main reasons for the deactivation of the catalyst without modification. On the other hand, modification by the MgO promoter improved the dispersion of the Ni0 species, and enhanced the CO2 adsorption affinity which in turn depressed the occurring of carbon deposition, and thus retarded the deactivation process.     

La2O3/γ-Al2O3催化剂用于二甲醚二氧化碳重整制氢

采用等体积浸渍法制备了不同负载量的La₂O₃/γ-Al₂O₃催化剂,并考察了负载量和反应温度对催化剂用于二甲醚二氧化碳重整制氢反应的性能影响。结果表明,反应温度为550℃、La₂O₃负载量为15%时,催化剂表现出最好的性能：二甲醚的转化率为100%,二氧化碳的转化率达到85.4%,产物氢气的选择性高达93.3%,一氧化碳的选择性为76.04%,副产物甲烷的选择性仅为6.3%。550 ℃时其平均积炭速率为1.387 5 mg/（g·h）。研究还利用XRD、BET、TEM、TG等方法对催化剂进行了表征。     

Kinetics of methane steam reforming on a Ni on alumina-titania catalyst

The kinetics of methane steam reforming on a nickel on alumina-titania catalyst, was studied in the range of 773–873 K. A Hougen-Watson type model gives good agreement with the experimental rates.     

Carbon deposition on a Ni/α-Al2O3 catalyst

The kinetics of carbon deposition over a Ni/α-Al₂O₃ commercial catalyst, has been studied using CH₄−H₂ gas mixtures in the range of 748–873 K. A Hougen-Watson type model gives good agreement with the experimental rates.     

Effect of Ni Loading and CexZr1-xO2 Promoter on Ni-Based SBA-15 Catalysts for Steam Reforming of Methane

A series of Ni/SBA-15 catalysts with Ni contents ranging from 5wt% to 20wt% as well as 10wt%Ni/10wt?xZn-xO2/SBA-15 (z=0, 0.5, 1) were prepared. The structures of the catalysts were characterized using XRD, TPR, TEM and BET techniques. The catalytic activities of the catalysts for steam reforming of methane were evaluated in a continuous flow microreactor. The results indicated that both the Ni/SBA-15 and the Ni/CexZr1-xO2/SBA-15 catalysts had good catalytic activities at atmospheric pressure. The 10wt%Ni/SBA-15 catalyst exhibited excellent stability at 800癈 for time on stream of 740 h. After the reaction, carbon deposits were not formed on the surface of the catalyst. There existed a regular hexagonal mesoporous structure in the Ni/SBA-15 and the Ni/CexZr1-xO2/SBA-15 catalysts. The nickel species and the CexZr1-xO2 component were all confined in the SBA-15 mesopores. The CexZr1-xO2 could promote dispersion of the nickel species in the Ni/CexZr1-xO2/SBA-15 catalysts.