La-Ni-Al钙钛矿氧化物中Sr和Ca取代La对甲醇重整的影响

Mixed perovskite oxides with CaxLa1-xNi0.3Al0.7O3-d and SrxLa1-xNi0.3Al0.7O3-d(x=0,0.2,0.5,0.8,and 1.0;d=0.5x)components have been prepared by a sol-gel method.The effects of the partial substitution of La by Ca and Sr in dry CH4 reforming were investigated at 500-800 ℃ and 101 kPa.The resulting oxides were examined by Fourier-transform infrared spectroscopy,X-ray diffraction,temperature-programmed reduction,scanning electron microscopy,energy dispersive X-ray spectrometry,and BET surface area analysis.Studies following the catalytic tests by carbon analysis show some carbon deposition on this catalytic system.The results indicate that all initial salt entered into a propionate structure,and that most of the solid solution has well defined perovskite structure with surface areas between 3.5 and 9.5 m2/g.Most of the catalysts performed well in the dry reforming,with CH4 conversions up to 90%,H2 yields up to 80%,and H2 selectivity up to 90%.Among the samples,Sr0.2La0.8Ni0.3Al0.7O2.9 showed an excellent catalytic performance in CH4 dry reforming,with a H2/CO ratio of 1,whereas Ca0.8La0.2Ni0.3Al0.7O2.6 showed the lowest coke formation(approximately 0.71%).     

流化床中高分散镍基催化剂上甲烷的自热重整和部分氧化

Highly dispersed Ni catalysts on spherical SiO2 were prepared by simple impregnation of Ni（acac）2, [Ni-（NH3）6-n（H2O）n]^2＋, [Ni（en）3]^2＋ and [Ni（EDTA）]^2-. Pulse adsorption of H2 and TEM analysis results confirmed that Ni was dispersed very well on the surface of SiO2 even after calcination （4 h） and reduction （1 h） at high temperature of 800 ℃. These highly dispersed and uniquely sized Ni crystallites were more stable and more reactive for both autothermal reforming and partial oxidation of methane in fluidized reactor.     

镍基钙钛矿型催化剂的结构调控及其在甲烷干重整反应中的应用

钙钛矿材料在催化领域具有广泛的应用,其微观结构的调控对催化性能有显著的影响.我们采用柠檬酸配合法、溶胶凝胶法、燃烧法和浸渍法一系列不同的制备过程对镍基钙钛矿材料的结构进行调控,并将其应用于甲烷干重整反应,研究了制备方法对活性组分Ni的化学形态、Ni与基底的相互作用以及活性氧物种的调控,进而影响其催化活性和抗积碳能力.结果表明,燃烧法可以显著提高催化剂的结晶度,从而提高Ni与基底的相互作用以及表面氧物种的含量,使其具有较强的抗积碳能力.燃烧法合成的Ni基钙钛矿催化剂在CH4∶CO2=1.25∶1,800℃的条件下反应300 h后,积碳量仅为1.0%,而在同样条件下浸渍法合成的催化剂积碳量则高达14.6%.     

Highly Dispersed Ni Nanoparticles on Anhydrous Calcium Silicate (ACS) Nanosheets for Catalytic Dry Reforming of Methane: Tuning the Activity by Different Ways of Ni Introduction

Three kinds of nickel‐loaded anhydrous calcium silicate nanocatalysts (ACS), including Ni‐ACS‐Dop, Ni‐ACS‐Iex and Ni‐ACS‐Im, were prepared by introducing Ni species through doping in the synthesis of calcium silicate hydrate (CSH) nanosheets, ion‐exchange with premade CSH nanosheets and deposition on calcined ACS nanosheets, respectively. Although Ni species were introduced in different ways, all the Ni‐ACS catalysts showed similar chemical compositions and microstructures, where Ni nanoparticles were highly dispersed on the ultrathin ACS nanosheets with a large surface area and good thermal stability. However, the differences in the way of Ni introduction did produce Ni with different electronic states. The Ni‐ACS‐Iex catalyst with “surface Ni” as a dominant form had more electrons enriched on the surface of Ni, which led to the highest activity in the dry reforming of methane (DRM) reaction among the three catalysts, whereas the Ni‐ACS‐Dop catalyst with “lattice Ni” as a dominant form showed an electron‐deficient property and lowest activity. Different from the introduction of a more favourable nanostructure or chemical component to the catalyst system, this work controlled the chemical environment of metal precursors and created metal catalysts with a preferred surface electronic state during synthesis, which could be a new strategy to improve the catalytic activity.     

Ni/La_2O_3/Al_2O_3催化剂上甲烷干重整积炭表征与分析(英文)

用传统的等体积浸渍法或蒸发法制备了Ni/La_2O_3/γ-Al_2O_3与Ni/La_2O_3/α-Al_2O_3催化剂,在没有稀释气体的条件下进行了甲烷干重整反应.采用H_2程序升温还原、N_2吸附脱附、X射线衍射、透射电子显微镜、热重-差示扫描热量以及程序升温加氢等手段对新鲜的与反应后的催化剂以及沉积的碳进行了表征.结果表明,催化剂上有四种含碳物种,以三种形态存在,即无定形碳(聚合态)、丝状碳或石墨碳.这些催化剂上积炭的数量与种类各不相同,依赖于催化剂中金属Ni颗粒的大小与载体的织构特性.丝状碳的形成及其形貌与金属Ni颗粒的大小有着密切的联系.Ni颗粒小于15nm时能抑制丝状碳的形成与沉积.减少积炭的数量,同时能产生较多的活性C_a物种,从而在一定程度上导致催化剂具有较好的活性与稳定性.     

制备高效稳定CO2重整甲烷Ni/ZrO2催化剂的新方法

 用超临界乙醇干燥ZrO(OH)2醇凝胶,可以制备出高效稳定的纳米复合型CO2重整甲烷Ni/ZrO2-AS催化剂; 在常压流动N2中加热处理ZrO(OH)2醇凝胶制备ZrO2前体,同样可以得到高效稳定的纳米复合型Ni/ZrO2-AN催化剂. 在270~650 ℃范围内改变ZrO(OH)2醇凝胶的热处理温度,对最终的Ni/ZrO2-AN催化剂的性能影响不大. 用这种方法制备纳米复合型Ni/ZrO2催化剂避免了复杂的超临界工艺,从而容易获得实际应用.     

碳化镍钼催化剂的制备及其甲烷干气重整活性(英文)

Nickel molybdenum carbide catalysts were prepared and their activities in the CO2 reforming of methane at a low CO2/CH4 reactant ratio were investigated using a microreactor at atmospheric pressure and at 973 K.The effect of the catalyst preparation method and the Ni/Mo ratio on the increase in catalyst life and the promotion of catalytic activity were investigated using N2 adsorption,X-ray diffraction, temperature-programmed carburization,temperature-programmed reaction,and a reforming reaction.The 25Ni75Mo catalyst that was carburized at 813 K exhibited the highest hydrogen formation ability and gave the least carbon deposition.The incomplete carburization of the Mo oxide species in the catalyst that was carburized at a lower temperature gradually gave a more active carburized species.The NiMoOxCy in the catalyst was more active in hydrogen formation during the dry reforming of methane whileβ-Mo2C andη-Mo3C2 were less active.     

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.     

不同方法制备的Ni／ZrO2-CeO2-Al2O3催化剂对CH4-CO2重整反应的催化性能

 采用水热合成法、溶胶凝胶法和共沉淀－负载法制备了相同NiO含量的Ni／ZrO2－CeO2－Al2O3催化剂，考察了它们在CH4－CO2重整反应中的催化性能及稳定性，测定了积碳量．用CO2程序升温脱附方法测试了它们的CO2吸附性能，用H2程序升温脱附方法测试了表面Ni的分散度．结果表明，随温度升高，CH4和CO2转化率降低的顺序是：溶胶凝胶法≈共沉淀－负载法＞水热合成法，并且反应产物中n（CO）／n（H2）比随温度升高而降低．水热法和共沉淀－负载法制备的催化剂稳定性好，且前者的活性比后者高；溶胶凝胶法制得的催化剂活性较高，但易失活．积碳量大小顺序是：水热法＞溶胶凝胶法＞共沉淀－负载法．与其他方法制备的催化剂相比，水热法制备的催化剂对CO2的吸附量更大，\r\n而且积碳主要存在于载体上，从而保证了催化剂的稳定性．     

Promotion Effects of Nickel Catalysts of Dry Reforming with Methane

The promotion effects of nickel catalyst of dry reforming with methane were extensively investigated by means of XRD, SEM, EDX, N₂‐adsorption and H₂‐adsorption. XRD characterization indicated that good dispersion of nickel oxide and MgO promoter is achieved over γ‐Al₂O₃ support. Addition of MgO promoter effectively retards the formation of NiAl₂O₄ phase. SEM and EDX analysis exhibited that the addition of rare‐earth metal oxide CeO₂ effectively promotes the Ni metal dispersion on the surface of the catalysts despite of undesirable self‐dispersion of CeO₂ promoter. Furthermore, the nickel component is gradually dispersed on the surface of the support following the exposure to reaction gas mixture for a period of time. The addition of MgO inhibited the self‐dispersion and promotion effect of CeO₂ on Ni dispersion on the catalysts. H₂ chemisorption revealed that the addition of the alkaline oxide MgO promoter significantly prohibits the metal dispersion on the catalyst. Inappropriate promoter addition can result in sharp decrease of the metal dispersion, N₂‐adsorption indicated that oxide promoter was mostly concentrated on the outer layer of the alumina support while the nickel metal was generally dispersed in the support pores. Addition of promoters contributed to more reduction in mesopore volume.     

Mechanism of Separate Interaction of Oxygen and Methane with the Perovskite Catalyst SrCoO3−x Modified by Alkali Metals

We have studied the initial steps of activation of O₂ and CH₄ on strontium cobaltite, with the perovskite structure and modified by alkali metals, under nonsteady-state conditions using a TAP reactor (TAP = Temporal Analysis of Products). We have established that adsorption of oxygen can be described by a three-step mechanism including intermediate formation of molecularly adsorbed oxygen followed by its dissociation and insertion of atomically adsorbed oxygen into the interior of the catalyst. The kinetics of reaction of methane with the oxidized catalyst is described satisfactorily by a first-order equation.     

甲烷干重整催化剂Ni/Al2O3表面积炭表征与分析

用蒸发法制备了Ni/Al2O3催化剂及浸渍法制备了Ni/α-Al2O3和Ni/γ-Al2O3催化剂, 并与商品天然气水蒸气重整催化剂Z118Y一起进行了甲烷干重整实验, 考察了各催化剂上表面积炭行为. 通过H2程序升温还原(H2-TPR)、BET(Brunauer-Emmett-Teller)比表面积分析、X射线衍射(XRD)、透射电镜(TEM)、热重-差式扫描量热(TG-DSC)、程序升温氢化(TPH)等表征手段对催化剂表面沉积炭的特性进行了表征. 结果表明, 各催化剂上至少存在三种形式的碳物种: 无定形碳、丝状碳及石墨碳. 由于载体性质不同, 各催化剂上沉积炭的种类及其含量有所差别. Z118Y、Ni/Al2O3及Ni/α-Al2O3催化剂上主要沉积丝状炭, 而Ni/γ-Al2O3催化剂上则主要是石墨碳. Ni/γ-Al2O3催化剂中金属Ni颗粒较小(小于15 nm)、粒径分布范围较窄、分散性较好, 能减少催化剂表面炭的沉积, 有效地抑制丝状碳的生长.     

高稳定性Ni/SBA-15催化剂的结构特征及其对二氧化碳重整甲烷反应的催化性能

 采用浸渍法制备了Ni含量为2.5%～20%的系列Ni/SBA-15催化剂,在常压连续流动固定床反应器上考察了催化剂对二氧化碳重整甲烷制合成气的催化性能,并用X射线衍射和N2吸附法研究了Ni/SBA-15催化剂的结构特征. 结果表明, Ni/SBA-15催化剂具有很高的CH4和CO2转化率, 12.5%Ni/SBA-15催化剂在800 ℃反应600 h后活性没有明显下降,但反应710 h后CH4的转化率下降了约50%, CO2的转化率下降了约25%. 其活性下降的主要原因是催化剂积炭. 在高温条件下反应时, SBA-15的介孔结构也没有遭到破坏,分子筛的孔壁能有效阻止活性组分Ni的团聚. SBA-15孔中组装一定量的Ni活性组分后,除了SBA-15的介孔外,还会形成另外一种较小的孔,但这不影响SBA-15的有序介孔结构,只是其孔径、孔容和BET比表面积降低.     

CO2 Reforming of CH4 over Nickel and Cobalt Catalysts Prepared from La—Based Perovskite Precursors

Four perovskite-type complex oxides (LaNiO3, La2NiO4, LaCoO3 and La2CoO4) were successfully prepared using two sol-gel methods, the Pechini method (PC) and the citric acid complexing method (CC). The catalysts were characterized by XRD and TPR. After reduction, the activity of the catalysts in the CO2 reforming of methane was tested. Ni-based catalysts from La2NiO4 precursors were the most active and stable catalyst after calcination above 850 癈, which gave a methane conversion of 0.025 mmol/(g-s) for those prepared by the PC method and 0.020 mmol/(g-s) by the CC method. It was proposed that the well-defined structure and lower reducibility is responsible for the unusual catalytic behavior observed over the pre-reduced La2NiO4 catalyst.     

光热催化甲烷干重整研究进展

随着工业化的推进,化石能源的消耗产生大量温室气体,其中CH₄和CO₂占据温室气体排放的98%以上。将CH₄和CO₂转化为高附加值化学品具有重要的意义,一直受到工业界和学术界广泛关注。传统的热催化甲烷干重整(DRM)可实现将CH₄和CO₂转化为合成气,但该反应过程受热力学限制,需要很高的能量输入,并且由于反应温度较高,催化剂易发生积碳而失活。绿色环保的光催化技术可以使甲烷干重整反应在温和条件下进行,但是存在太阳光利用率和反应转化率较低等问题。最近光热协同催化受到学术界广泛关注。许多研究结果表明,在相对温和的条件下,光热催化DRM可以获得良好的催化效果,可有效实现太阳能转化为化学能。本文简要介绍近期光热催化甲烷干重整反应的研究进展,总结不同金属催化剂在光热催化甲烷干重整中的应用,同时提出了光热催化甲烷干重整存在的一些挑战及展望。     

Carbon Dioxide Reforming of Methane to Synthesis Gas Over Ni/MgO-Al2O3-AlPO4 Catalysts

Carbon dioxide reforming of methane to synthesis gas was studied over Ni/MgO-Al₂O₃-AlPO₄ catalysts. The conventional Ni/Al₂O₃ and Ni/MgO-Al₂O₃ catalysts were included for comparison. These catalysts were characterized by nitrogen adsorption and hydrogen chemisorption. The results show that Ni/MgO-Al₂O₃-AlPO₄ was more active than the other two catalysts especially at high reaction temperatures. MgO-Al₂O₃-AlPO₄ has a large pore diameter with a very uniform pore size distribution. It can overcome the pore diffusion effect under high temperature reaction conditions.     

NiO-MgO固溶体的形成对Ni/MgO-AN催化CO2重整CH4反应活性和稳定性的影响

 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,浸渍Ni(NO3)2后经不同温度焙烧得到Ni含量为8.8%的NiO/MgO样品,还原后制得Ni/MgO-AN催化剂. 采用XRD和TPR技术对NiO和MgO之间形成的NiO-MgO固溶体进行了表征,并将Ni/MgO-AN催化剂用于催化CO2重整CH4反应. 结果表明,在低于650 ℃焙烧时, NiO不能完全溶入MgO中,NiO/MgO样品中存在自由的NiO粒子,还原态Ni/MgO-AN催化剂在CO2重整CH4反应中的稳定性低; 当样品焙烧温度等于或高于650 ℃时,NiO可以完全溶入MgO中形成NiO-MgO固溶体,还原态Ni/MgO-AN催化剂具有高稳定性.     

Ni3Al箔在甲烷重整反应中的催化性能

研究了以冷轧工艺制备的Ni₃Al单晶箔(Ni-24at% Al), 以及表面预处理(873 K下蒸汽氧化后还原处理)后的Ni₃Al箔, 在甲烷重整制氢反应中的催化性能. 首先, 采用逐步升温法研究了873～1173 K下Ni₃Al箔的催化活性与温度的关系; 然后, 采用等温法研究了973 K下Ni₃Al箔的催化稳定性. 根据催化反应和扫描电镜显微观察的结果得出: 未经预处理和经过预处理的Ni₃Al箔, 在反应中均显示出一定的催化活性和稳定性; 表面预处理对Ni₃Al箔的催化活性有显著的增强作用, 原因是经过该预处理后的Ni₃Al箔形成了富Ni表面; Ni₃Al箔在甲烷重整反应的气氛中, Ni原子从Ni₃Al基体向表面的移动, 是维持催化活性的主要原因.     

Study on the Reaction Mechanism for Carbon Dioxide Reforming of Methane over supported Nickel Catalyst

The adsorption and dissociation of methane and carbon dioxide for reforming on nickel catalyst were extensively investigated by TPSR and TPD experiments. It showed that the decomposition of methane results in the formation of at least three kinds of surface carbon species on supported nickel catalyst, while CO2 adsorbed on the catalyst weakly and only existed in one kind of adsorption state. Then the mechanism of interaction between the species dissociated from CH4 and CO2 during reforming was proposed.