甲烷快速部分氧化重整试验研究

采用常规浸渍法制备了Rh/α-Al2O3催化剂,建立了甲烷快速部分氧化重整试验体系。通过控制变量法,考察了甲烷快速部分氧化重整反应中反应条件参数(CH4/O2、反应气体预混合温度、空速)变化对反应物的转化率、反应产物及分布的影响。试验结果表明,在试验条件下,CH4的转化率始终大于85%,O2转化率接近100%,CO的选择性为85%左右,H2的选择性为40%～60%。反应过程大致为催化剂入口处的部分氧化反应和下游的水蒸气重整,大部分的CO由部分氧化产生,而H2的产生受水蒸气重整反应的影响较大;随着反应温度的上升,CH4的转化率上升,CO,H2的选择性也上升;随着空速的增大,H2的选择性减小,表明甲烷催化部分氧化反应是一个受传质控制的反应。     

甲烷催化制氢气的研究进展

阐述了甲烷催化制氢技术研究取得的主要进展，对各种制氢工艺方法、催化剂的种类和性能、反应器的类型、催化剂积炭等方面进行了详细的论述。     

甲烷部分氧化制氢机理及方法

就甲烷部分氧化制氢的机理和方法进行了讨论,对甲烷部分氧化制氢各种工艺的研究现状进行了阐述,能对寻找经济性较好的制氢方法有所启发,引发对甲烷部分氧化制氢机理和方法的讨论与研究：     

微细通道内氢气辅助甲烷催化氧化的数值模拟

对微圆管内低浓度氢气、甲烷混合气在铂表面的催化氧化进行了数值模拟,重点研究了添加氢气对甲烷反应的影响机理.结果表明,氧气占据空位活性中心抑制了甲烷的吸附,导致较高的催化着火温度;氢气的掺入可以降低甲烷氧化反应的起始温度和着火温度;在铂催化剂表面,甲烷的催化氧化发生在氢气的燃烧过程中,氢气在燃烧过程中消耗氧气,为甲烷的反应提供必需的空位活性中心(Pt(s));甲烷的着火主要受其自身的激发,甲烷着火以前,壁面活性中心几乎全被氧占据,而甲烷着火以后,O(s)和Pt(s)同为主要壁面组分.     

整体型催化剂上甲烷自热氧化制合成气

用镍金属制备了一整体催化剂并与负载铑和铂比较了甲烷氧化制合成气的性能。结果表明,镍金属催化剂上甲烷转化率、H2和CO的选择性与铑催化剂相当,而且稳定性非常好。反应中加入H2O和CO2的实验表明,产物中H2／CO的比例可以直接调节。     

柴油氧重整及部分氧化重整制氢

以复合氧化物为载体,稀土元素等为催化剂助剂,采用浸渍法制备了铂镧系列催化剂并探索了还原方法;通过柴油氧重整制氢及柴油部分氧化重整制氢试验,研究了催化剂的抗氧化性、活性及稳定性;研究了温度、水碳比、柴油液空速和氧碳比四因素对柴油部分氧化重整制氢的影响;研究了制氢过程的析碳及除碳方法.     

MnO_x/ZSM-5催化剂催化NO氧化性能的研究

为实现快速选择性催化还原(SCR)反应条件,开发低成本NO氧化催化剂,采用浸渍法制备了不同Mn负载量的MnO_x/ZSM-5催化剂,采用电感耦合等离子体(ICP)、X射线衍射(XRD)、扫描电子显微镜(SEM)和N_2吸附/脱附等技术对催化剂特征进行了表征,并考察了其催化NO氧化活性.结果表明:Mn负载量对MnO_x/ZSM-5催化剂催化NO氧化的活性有显著影响,较高的负载量可以提供更多的反应中心,但过高的负载量会导致活性组分在催化剂表面积聚,减小催化剂比表面积和降低表面分散度.Mn负载量为5.2%的样品表现出最佳的NO催化氧化效率,400℃下NO转化率达到50.6%,但低温下催化NO氧化活性较差,还需进一步优化制备条件,以提高MnO_x/ZSM-5催化剂的反应性能.     

甲烷催化燃烧锅炉用催化剂的研究

催化燃烧是一种高效、低排放的新兴技术,可应用于天然气发电。利用共沉淀法制备了系列Ce—Zr复合氧化物,并用XRD和SEM等手段对其进行了表征,测试了其催化甲烷燃烧性能。结果表明,部分铈离子可进入氧化锆晶格中形成锆基固溶体。当游离的CeO2较好地分散在氧化锆基固溶体上时,铈锆催化剂具有较好的催化甲烷燃烧性能。Ce0.6Zr0．4O2催化剂显示了这种协同作用,获得了较低起燃温度（318℃）和完全转化温度（530℃）。     

甲烷在炭黑上催化裂解的热重研究

采用几种商用炭黑作为甲烷催化裂解反应的催化剂并进行了测试,使用热重分析法研究了甲烷裂解反应过程中炭黑样品活性的变化,并用氮气吸附脱附法、X射线衍射仪和扫描电镜分别分析了样品孔结构、晶体结构及微观特征随反应的变化.所测试的样品在1 073～1 173 K的温度下有较强的初始反应活性,随后反应活性随着增重增加而下降,一段时间后,活性降低30%～40%.得到了动力学参数:反应级数为0.5,活化能为213～222 kJ/mol.积炭使炭黑球粒径增长,并降低了比表面积和总表面积.甲烷在炭黑上裂解存在两个反应阶段,两个阶段活性中心的性质不同.     

铜渣催化甲烷二氧化碳重整的热力学及动力学分析

以铜渣作为甲烷二氧化碳重整的催化剂及热源,考察其催化重整活性,并对铜渣进行了XRD,SEM,BET,H2-TPR分析表征。实验结果表明,铜渣在高温段具有较高的催化活性,当铜渣温度为1 200℃时,甲烷、二氧化碳转化率分别为87.5%和85.2%。同时,对铜渣催化甲烷二氧化碳重整进行了热力学及动力学分析,得出铜渣从1 200℃降至600℃过程中余热利用率为22.93%,铜渣催化该重整反应的活化能为213.90 k J·mol~(-1),反应速率常数k=2.19exp(-213.90/RT)。     

Catalyst deactivation in on-board H2 production by fuel dehydrogenation

The production of H₂ for on-board application is a very interesting challenge for industrial and academic researchers. The aim is the application of on-board hydrogen production on the airplanes using kerosene as H₂ source. In this work an in depth study into the partial dehydrogenation (PDH) of two hydrocarbons blends and desulfurized JetA1 fuel has been performed by using 1 wt.%Pt–1 wt.%Sn/γ-Al₂O₃ and 1 wt.%Pt–1 wt.%Sn–0.5%K/γ-Al₂O₃ to find a way to produce H₂ “on-board” for the feeding of the fuel-cell apparatus. The mechanism of deactivation by coke was studied in depth combining Raman spectroscopy and Temperature-programmed oxidation (TPO) analyses. Microstructure analysis of metallic particles in fresh and deactivated catalysts was investigated by HRTEM. Relatively high H₂ partial pressure increases catalyst life by controlling full dehydrogenation coke-forming reaction. By feeding model organic molecules, it was possible to identify the contribution of each class of compounds to the H₂ production as well as the amount and type of coke formed. A relatively complex reaction pathway, which is able to evidence the role of different sites and reactions involved in PDH processes, was proposed.     

Properties and H2 production ability of Pt photodeposited on the anatase phase transition of nitrogen-doped titanium dioxide

The effect of calcination temperature on the properties and H₂ production ability of nitrogen-doped (N-doped) titanium dioxide (TiO₂) photodeposited with 0.2 wt% Pt (platinum) was studied. The increase in crystallinity of pre-calcinated N-doped TiO₂ initiated at temperatures higher than 131 °C transformed the morphology from anomalous nanostructure to texture composed of nanoparticles and enhanced the specific surface areas. At 200-400 °C, the anatase peaks gradually became sharper and the visible light absorption region decreased due to the growth of crystallites and the decrease of N-doping content, respectively. Maximum H₂ production was reached when N-doped TiO₂ was calcined at 200 °C followed by Pt photodeposition. The maximum condition is brought about by the formation of textures consisting of nanoparticles and a broad absorption region, thus creating superior active sites for photocatalytic H₂ production.     

A Study of CH_4 Partial Oxidation Reforming with Detailed Mechanisms

IntotuctriEnergy-efficient refondng Of Cab into syn-gas isof po pehcal impo~ce. Partial oxidationrefondng is a mild exothennic Process, that may be analternative tO steam refoedng or CO, refondng, both,of which are highly endothennic. A theoretical HzlCOProduct ratio of 2 is another advantage of Cd pAnaloaldation refondng, which is more suitable for manydownstream processes. Several investigators haveoffered economic analyses of catalytic pAnal oaldationrefondng for methanol Produchon[']…     

Durability of solid oxide fuel cells using sulfur containing fuels

The usability of hydrogen and also carbon containing fuels is one of the important advantages of solid oxide fuel cells (SOFCs), which opens the possibility to use fuels derived from conventional sources such as natural gas and from renewable sources such as biogas. Impurities like sulfur compounds are critical in this respect. State-of-the-art Ni/YSZ SOFC anodes suffer from being rather sensitive towards sulfur impurities. In the current study, anode supported SOFCs with Ni/YSZ or Ni/ScYSZ anodes were exposed to H₂S in the ppm range both for short periods of 24 h and for a few hundred hours. In a fuel containing significant shares of methane, the reforming activities of the Ni/YSZ and Ni/ScYSZ anodes were severely poisoned already at low H₂S concentrations of ∼2 ppm H₂S. The poisoning effect on the cell voltage was reversible only to a certain degree after exposure of 500 h in the state-of-the-art cell, due to a loss of percolation of Ni particles in the Ni/YSZ anode layers closest to the electrolyte. Using SOFCs with Ni/ScYSZ anodes improved the H₂S tolerance considerably, even at larger H₂S concentrations of 10 and 20 ppm over a few hundred hours.     

The pseudo-catalytic promotion of nitric oxide oxidation by ethane at low temperatures

Experimental work carried out in a flow reactor has shown that, from 700 to 750 K, low concentrations of ethane can act as a virtual catalyst in effecting the oxidation of NO to NO₂. That is, while there is strong promotion of the oxidation of NO, there is very little concurrent degradation of the ethane. This contrasts with other experimental and modeling investigations, in which promotion by the hydrocarbon of NO oxidation has accompanied oxidation of a considerable fraction of the hydrocarbon. The rate of this pseudo-catalytic effect is significantly affected by the concentrations of both ethane and oxygen, which in this study ranged from 0 to 70% for [O₂], 0 to 5000 ppm for [C₂H₆], and 0 to 350 ppm for [NO]. The level of reaction achieved under the various conditions was measured in terms of the rates of formation of NO₂ and C₂H₄. Current kinetic mechanisms, though displaying good accuracy in other temperature regimes, fail to predict this pseudo-catalytic behavior of ethane, indicating that several elementary reactions important at the low temperatures are missing or poorly represented in such mechanisms. Mechanistic modifications are discussed and allow the measurements to be simulated more closely than with existing reaction schemes. It has been shown that the relative rates of the competing reactions C₂H₅ + O₂ → C₂H₄ + HO₂ and C₂H₅ + O₂ (+M) → C₂H₅O₂ + (M) are of critical importance in this situation.     

Hydrogen production by catalytic processing of renewable methane-rich gases

Biomass-derived methane-rich gases such as landfill gas (LFG), biogas and digester gas are promising renewable resources for near-future production of hydrogen. The technical and economical feasibility of hydrogen production via catalytic reforming of LFG and other methane-rich gases is evaluated in this paper. The thermodynamic equilibrium calculations and experimental measurements of reformation of methane-rich CH₄–CO₂ mixtures over Ni-based catalyst were conducted. The problems associated with the catalyst deactivation due to carbon lay down and effects of steam and oxygen on the process sustainability were explored. Two technological approaches distinguished by the mode of heat input to the endothermic process (i.e., external vs autothermal) were modeled using AspenPlus^TM${\mathrm{AspenPlus}}^{\mathrm{TM}}$ chemical process simulator and validated experimentally. A 5 kW_th pilot unit for hydrogen production from LFG-mimicking CH₄–CO₂ mixture was fabricated and operated. A preliminary techno-economic assessment indicates that the liquid hydrogen production costs are in the range of $3.00–$7.00 per kilogram depending upon the plant capacity, the process heat input option and whether or not carbon sequestration is included in the process.     

Combined catalytic partial oxidation and CO2 reforming of methane over ZrO2-modified Ni/SiO2 catalysts using fluidized-bed reactor

Nickel on zirconium-modified silica was prepared and tested as a catalyst for reforming methane with CO₂ and O₂ in a fluidized-bed reactor. A conversion of CH₄ near thermodynamic equilibrium and low H₂/CO ratio (1<H₂/CO<2) were obtained without catalyst deactivation during 10 h, in a most energy efficient and safe manner. A weight loading of 5 wt% zirconium was found to be the optimum. The catalysts were characterized using X-ray diffraction (XRD), H₂-temperature reaction (H₂-TPR), CO₂-temperature desorption (CO₂-TPD) and transmission election microscope (TEM) techniques. Ni sintering was a major reason for the deactivation of pure Ni/SiO₂ catalysts, while Ni dispersed highly on a zirconium-promoted Ni/SiO₂ catalyst. The different kinds of surface Ni species formed on ZrO₂-promoted catalysts might be responsible for its high activity and good resistance to Ni sintering.     

Effect of H2O2 on Pt electrode dissolution in H2SO4 solution based on electrochemical quartz crystal microbalance study

The effect of H₂O₂ on the Pt dissolution in 0.5 mol dm⁻³ H₂SO₄ was investigated using an electrochemical quartz crystal microbalance (EQCM). For the potential cycling at 50 mV s⁻¹, the Pt weight irreversibly decreases in a N₂ atmosphere with H₂O₂, while only a negligible Pt weight-loss is observed in the N₂ and O₂ atmospheres without H₂O₂. The EQCM data measured by the potential step showed that the Pt dissolution in the presence of H₂O₂ depends on the electrode potential and the H₂O₂ concentration. For the stationary electrolysis, the Pt dissolution occurs at 0.61–1.06 and 1.06–1.36 V vs. RHE. It should be noted that the Pt dissolution phenomenon in the presence of H₂O₂ is also affected by the potential scanning time. Based on these results, H₂O₂ is considered not only to contribute to the formation of Pt-oxide causing the cathodic Pt dissolution, but also to participate in the anodic Pt dissolution and the chemical Pt dissolution.     

Reactivity of Ce-ZrO2 (doped with La-, Gd-, Nb-, and Sm-) toward partial oxidation of liquefied petroleum gas: Its application for sequential partial oxidation/steam reforming

Ce-ZrO₂ was found to have useful partial oxidation activity under moderate temperatures. It converted liquefied petroleum gas (LPG) to H₂, CH₄, CO and CO₂ with small amounts of C₂H₆ and C₂H₄ formations depending on the operating temperature and provided significantly greater resistance toward carbon deposition compared to conventional Ni/Al₂O₃. The doping of La, Sm and Gd over Ce-ZrO₂ considerably improved catalytic reactivity, whereas Nb-doping reduced its reactivity. It was found that the impact of doping element is strongly related to the degrees of oxygen storage capacity (OSC) and/or lattice oxygen (O_O^x) of materials. Among all catalysts, La-doped Ce-ZrO₂ was observed to have highest OSC value and was the most active catalyst. Above 850 °C with inlet LPG/O₂ molar ratio of 1.0/1.0, the main products from the reaction over La-doped Ce-ZrO₂ were H₂, CH₄, CO, and CO₂.     

Comparative study on the promotion effect of Mn and Zr on the stability of Ni/SiO2 catalyst for CO2 reforming of methane

The stability of Mn-promoted Ni/SiO₂ catalyst for methane CO₂ reforming was investigated comparatively to that of Zr-promoted Ni/SiO₂. The catalysts were prepared by the same impregnation method with the same controlled promoter contents and characterized by TPR, XRD, TG, SEM, XPS and Raman techniques. The addition of Mn to Ni/SiO₂ catalyst promoted the dispersion of Ni species, leading to smaller particle size of NiO on the fresh Ni–Mn/SiO₂ catalyst and the formation of NiMn₂O₄, which enhanced the interaction of the modified support with Ni species. Thus, the Ni–Mn/SiO₂ catalyst showed higher activity and better ability of restraining carbon deposition than Ni/SiO₂ catalyst. Besides, it exhibited stable activity at reaction temperatures over the range from 600 °C to 800 °C. However, the introduction of Zr increased the reducibility of Ni–Zr/SiO₂, and the catalyst deactivated much more dramatically when the reaction temperature decreased due to its poor ability of restraining carbon deposition, and its activity decreased monotonically with time on stream at 800 °C.