面向氢能源、燃料电池和二氧化碳减排的制氢途径的选择

对氢气的多种制造途径加以探讨,也涉及到氢能的利用、燃料电池以及二氧化碳的减排。需要指出的是氢气并非能源,而只是能量的载体。 所以氢能的发展首先需要制造氢气。对于以化石燃料为基础的制氢过程,如煤的气化和天然气重整,需要开发更经济和环境友好的新过程,在这些新过程中要同时考虑二氧化碳的有效收集和利用问题。对于煤和生物质,在此提出了一种值得进一步深入研究的富一氧化碳气化制氢的概念。对于以氢为原料的质子交换膜燃料电池系统,必须严格控制制备的氢气中的一氧化碳和硫化氢;对于以烃类为原料的固体氧化物燃料电池,制备的合成气中的硫也需严格控制。然而,传统的脱硫方法并不适宜于这种用于燃料电池的极高深度的氢气和合成气的脱硫。氢能和燃料电池的发展是与控制二氧化碳排放紧密相关的。     

一种适用于生物油低温制氢的碳纳米纤维促进的镍催化剂

氢气作为一种高热值的清洁能源广泛地应用于工业中. 研究证明: 生物质通过化学过程可以转化为多种气体燃料(氢气), 液体燃料以及高附加值的化学品. 生物质作为一种环境友好型再生洁净能源, 其研究越来越受到关注. 本文旨在探讨利用生物油为原料, 通过水蒸汽重整方法制备富氢合成气的过程. 利用均匀浸渍的方法制备了一种高分散的碳纳米纤维促进的镍(Ni/CNFs)催化剂, 并将普通的Al₂O₃作为载体的Ni/Al₂O₃催化剂和Ni/CNFs作对比. 研究了重整温度以及水蒸汽和碳摩尔比(n_S/n_C)对生物油水蒸汽重整制氢的影响. 结果表明: 碳纳米纤维作为载体用于生物油水蒸汽重整制氢的效果要远优于普通的Al₂O₃载体, 利用22% Ni/CNFs 催化剂时, 在实验温度范围内(350-550℃), 最高生物油转化率和氢气产率分别达到了94.7%和92.1%, 通过研究重整条件以及对催化剂进行表征探讨了生物油在水蒸汽重整过程中催化剂的构效关系.     

Ceramic microreactors for on-site hydrogen production from high temperature steam reforming of propane

The steam reforming of hydrocarbon fuels is a promising method for the production of hydrogen for portable electrical power sources. A suitable reactor for this application, however, must be compatible with temperatures above 800 degrees C to avoid coking of the catalytic structures during the reforming process. Here, ceramic microreactors comprising high surface area, tailored macroporous SiC porous monoliths coated with ruthenium (Ru) catalyst and integrated within high-density alumina reactor housings were used for the steam reforming of propane into hydrogen at temperatures between 800 and 1000 degrees C. We characterized these microreactors by studying C3H8 conversion, H2 selectivity, and product stream composition as a function of the total inlet flow rate, steam-to-carbon ratio (S/C), and temperature. As much as 18.2 sccm H2, or 3.3 x 104 sccm H2 per cm3 of monolith volume, was obtained from a 3.5 sccm entering stream of C3H8 at a S/C of 1.095 and temperatures greater than 900 degrees C. Operating at a S/C close to 1 reduces the energy required to heat excess steam to the reaction temperature and improves the overall thermal efficiency of the fuel processor. Kinetic analysis using a power law model showed reaction orders of 0.50 and -0.23 with respect to propane and steam, respectively, indicating that the rate limiting step in the steam reforming reaction is the dissociative adsorption of propane on the Ru catalyst. The performance of the microreactor was not affected after exposure to more than 15 thermal cycles at temperatures as high as 1000 degrees C, and no catalyst deactivation was observed after more than 120 h of continuous operation at 800 degrees C, making these ceramic microreactors promising for efficient on-site hydrogen production from hydrocarbons for use in polymer electrolyte membrane (PEM) fuel cells.     

Highly Active Steam Reforming Catalyst for Hydrogen and Syngas Production

Toyo Engineering Corporation developed a steam reforming catalyst, which is four times as active as conventional catalysts, for hydrogen and syngas production from light natural gas. The catalyst has over three years experience in 1500 t/d class NH₃ plant. Benefits, such as fuel saving, etc., by the developed catalyst are discussed.     

Hydrogen Production by Catalytic Reforming of Gaseous Hydrocarbons (Methane &; LPG)

Hydrogen has been attracting great interest as a major energy source in near future. The lack of an infrastructure has led to a research effort to develop fuel processing technology for production of hydrogen. In this review, we are reporting the catalytic reforming of gaseous hydrocarbons carried out in our research group, covering dry-reforming of CH₄, tri-reforming of CH₄, the electrocatalytic reforming of CH₄ by CO₂ in the SOFC (solid oxide fuel cell) system and steam reforming of LPG. Especially, we have focused on our work, though the related work from other researchers is also discussed wherever necessary. It was found that tri-reforming of CH₄ over NiO–YSZ–CeO₂ catalyst was more desirable than dry-reforming of CH₄ due to higher reforming activity and less carbon formation. The synthesis gas produced by tri-reforming of CH₄ can be used for the production of dimethyl ether, Fischer–Tropsch synthesis fuels and high valued chemicals. To improve the problem of deactivation of catalyst due to carbon formation in the dry reforming of CH_4, the internal reforming of CH₄ by CO₂ in SOFC system with NiO–YSZ–CeO₂ anode catalyst was suggested for cogeneration of a syngas and electricity. It was found that Rh-spc-Ni/MgAl catalyst showed long term stability for 1,100 h in the steam reforming of LPG under the tested conditions. The addition of Rh to spc-Ni/MgAl catalyst restricted the deactivation of catalyst due to carbon formation in the steam reforming of LPG and diesel under the tested conditions. The result suggested that the developed reforming catalysts can be used in the reforming process of CH₄, LNG and LPG for application to hydrogen station and fuel processor system.     

Ni/Al2O3改性催化剂催化重整生物油模拟物制氢研究

制备了Ni/Al₂O₃、Ni-Cu/Al₂O₃、Ni-Co/Al₂O₃和Ni-Co-Cu/Al₂O₃催化剂,研究了Co和Cu对生物油水蒸气催化重整的影响。实验表明,Co 能促进水汽变换(WGS)反应,提高氢气的产率,Cu能抑制反应中焦炭的形成,提高催化剂的稳定性。对催化剂Ni-Co-Cu/Al₂O₃进行工艺条件考察,当900 ℃、水油比为6 g/g、质量空速(WHSV)为1 h^-1时,碳选择性达到87.5%,氢气产率达到84.2%,潜在氢气产率达到92.4%。     

甲烷三重整制合成气

甲烷三重整是利用CO₂-H₂O-O₂ 同时重整甲烷的过程。该工艺既可以生产H₂/CO 为1.5 —2.0的合成气,又可以缓解甚至消除催化剂的积炭,适合于更廉价地生产用于合成甲醇、二甲醚以及清洁燃料等下游产品的合成气。本文重点评述了近年来国内外甲烷三重整制合成气在热力学、催化剂、反应器、动力学等方面的研究进展,指出甲烷三重整反应在电厂烟气、煤层气、天然气综合利用方面具备良好前景,但要通过该过程实现廉价合成气的生产,仍需研制高活性、抗积炭性能强的催化剂,并对反应器进行改进,以及进行反应机理和反应动力学的深入研究。     

Methane oxidation at redox stable fuel cell electrode La0.75Sr0.25Cr0.5Mn0.5O(3-delta)

Because of its widespread availability, natural gas is the most important fuel for early application of stationary fuel cells, and furthermore, methane containing biogases are one of the most promising renewable energy alternatives; thus, it is very important to be able to efficiently utilize methane in fuel cells. Typically, external steam reforming is applied to allow methane utilization in high temperature fuel cells; however, direct oxidation will provide a much better solution. Recently, we reported good electrochemical performance for an oxide anode La0.75Sr0.25Cr0.5Mn0.5O3 (LSCM) in low moisture (3% H2O) H2 and CH4 fuels without significant coking in CH4. Here, we investigate the catalytic activity of this oxide with respect to its ability to utilize methane. This oxide is found to exhibit fairly low reforming activity for both H2O and CO2 reforming but is active for methane oxidation. LSCM is found to be a full oxidation catalyst rather than a partial oxidation catalyst as CO2 production dominates CO production even in CH4-rich CH4/O2 mixtures. X-ray adsorption spectroscopy was utilized to confirm that Mn was the redox active species, clearly demonstrating that this material has the oxidation catalytic behavior that might be expected from a Mn perovskite and that the Cr ion is only present to ensure stability under fuel atmospheres.     

Hydrogen Production by Catalytic Reforming of Liquid Hydrocarbons

In this review, we are reporting the catalytic reforming of liquid hydrocarbon fuels carried out in our research group, covering the catalytic reforming of iso-octane and toluene as surrogate of gasoline, gasoline fuel processor system and steam reforming of n-hexadecane and decahydronaphthalene, main constituents of diesel. The commercial ICI reforming catalyst is prone to be poisoned by sulfur contained in iso-octane. We investigated various supported transition metal formulations and developed Ni/Fe/MgO/Al₂O₃ (KIST-5) catalyst with prolonged catalytic stability (>760 h), higher activity and sulfur tolerance ability over commercial ICI and HT catalysts for ATR reaction of iso-octane. We found that the concentration of CO can be reduced to <1,800 ppm by the gasoline fuel processor system charged with KIST-5 reforming catalyst, commercial HTS catalyst and KIST Pt–Ni/CeO₂ LTS catalyst. The addition of Rh metal to spc-Ni/MgAl catalyst as promoter was found to be very effective in inhibiting the deactivation of spc-Ni/MgAl catalyst by sintering of reduced Ni metal at high temperature during steam reforming of n-hexadecane. A 0.3 wt% Rh loading on spc-Ni/MgAl catalyst was optimized to have the best performance for steam reforming of n-hexadecane among the prepared catalysts. The addition of Rh to spc-Ni/MgAl catalyst also restricted the deactivation of the catalyst due to carbon formation at high reaction temperature. In view point of prolonged stability and higher activity, these developed reforming catalysts have a good scope in the reforming process of gasoline and diesel for hydrogen station and fuel processor system applications.     

Catalysis in high-temperature fuel cells

Catalysis plays a critical role in solid oxide fuel cell systems. The electrochemical reactions within the cell--oxygen dissociation on the cathode and electrochemical fuel combustion on the anode--are catalytic reactions. The fuels used in high-temperature fuel cells, for example, natural gas, propane, or liquid hydrocarbons, need to be preprocessed to a form suitable for conversion on the anode-sulfur removal and pre-reforming. The unconverted fuel (economic fuel utilization around 85%) is commonly combusted using a catalytic burner. Ceramic Fuel Cells Ltd. has developed anodes that in addition to having electrochemical activity also are reactive for internal steam reforming of methane. This can simplify fuel preprocessing, but its main advantage is thermal management of the fuel cell stack by endothermic heat removal. Using this approach, the objective of fuel preprocessing is to produce a methane-rich fuel stream but with all higher hydrocarbons removed. Sulfur removal can be achieved by absorption or hydro-desulfurization (HDS). Depending on the system configuration, hydrogen is also required for start-up and shutdown. Reactor operating parameters are strongly tied to fuel cell operational regimes, thus often limiting optimization of the catalytic reactors. In this paper we discuss operation of an authothermal reforming reactor for hydrogen generation for HDS and start-up/shutdown, and development of a pre-reformer for converting propane to a methane-rich fuel stream.     

固体氧化物燃料电池LSCM-CeO_2/Ni-ScSZ复合阳极制备及性能表征

采用双层流延法制备Ni-ScSZ阳极支撑层-ScSZ电解质复合膜.在烧结的Ni-ScSZ阳极支撑层表面丝网印刷一层LSCM-CeO2阳极催化层,得到LSCM-CeO2/Ni-ScSZ功能梯度层阳极.研究表明,LSCM/CeO2比为1:3(bymass)的功能梯度层阳极Ni-ScSZ13具有较佳的性能.单电池在850℃以H2和乙醇蒸气作燃料的最大功率密度分别为710和669mW/cm2,而LSCM/CeO2为1:0(bymass)的功能梯度层Ni-ScSZ10作阳极的单电池,最大功率密度分别为521和486m W/cm2.两种阳极单电池,分别在700℃于乙醇蒸气中作长时间运行实验,X-射线能量散射分析表明Ni-ScSZ13阳极比Ni-ScSZ10阳极具有较好的抗碳沉积性能.     

Mesoporous Nickel–Alumina Catalysts for Hydrogen Production by Steam Reforming of Liquefied Natural Gas (LNG)

Recent progress on the mesoporous nickel–alumina catalysts for hydrogen production by steam reforming of liquefied natural gas (LNG) was reported in this review. A number of mesoporous nickel–alumina composite catalysts were prepared by a single-step surfactant-templating method using cationic, anionic, and non-ionic surfactant as structure-directing agents for use in hydrogen production by steam reforming of LNG. For comparison, nickel catalysts supported on mesoporous aluminas were also prepared by an impregnation method. The effect of preparation method and surfactant identity on physicochemical properties and catalytic activities of mesoporous nickel–alumina catalysts in the steam reforming of LNG was investigated. Regardless of preparation method and surfactant identity, nickel oxide species were finely dispersed on the surface of mesoporous nickel–alumina catalysts through the formation of surface nickel aluminate phase. However, nickel dispersion and nickel surface area of mesoporous nickel–alumina catalysts were strongly affected by the preparation method and surfactant identity. It was found that nickel surface area of mesoporous nickel–alumina catalyst served as one of the important factors determining the catalytic performance in hydrogen production by steam reforming of LNG. Among the catalysts tested, a mesoporous nickel–alumina composite catalyst prepared by a single-step non-ionic surfactant-templating method exhibited the best catalytic performance due to its highest nickel surface area.     

Design of Multiple Metal Doped Ni Based Catalyst for Hydrogen Generation from Bio-oil Reforming at Mild-temperature

A new kind of multiple metal (Cu, Mg, Ce) doped Ni based mixed oxide catalyst, synthesized by the co-precipitation method, was used for efficient production of hydrogen from bio-oil reforming at 250-500 oC. Two reforming processes, the conventional steam reforming (CSR) and the electrochemical catalytic reforming (ECR), were performed for the bio-oil reforming. The catalyst with an atomic mole ratio of Ni:Cu:Mg:Ce:Al=5.6:1.1:1.9:1.0:9.9 exhibited very high reforming activity both in CSR and ECR processes, reaching 82.8% hydrogen yield at 500 oC in the CSR, yield of 91.1% at 400 oC and 3.1 A in the ECR, respectively. The influences of reforming temperature and the current through the catalyst in the ECR were investigated. It was observed that the reforming and decomposition of the bio-oil were significantly enhanced by the current. The promoting effects of current on the decomposition and reforming processes of bio-oil were further studied by using the model compounds of bio-oil (acetic acid and ethanol) under 101 kPa or low pressure (0.1 Pa) through the time of flight analysis. The catalyst also shows high water gas shift activity in the range of 300-600 oC. The catalyst features and alterations in the bio-oil reforming were characterized by the ICP, XRD, XPS and BET measurements. The mechanism of bio-oil reforming was discussed based on the study of the elemental reactions and catalyst characterizations. The research catalyst, potentially, may be a practical catalyst for high efficient production of hydrogen from reforming of bio-oil at mild-temperature.     

生物油水溶性组分的水蒸气催化重整制氢实验研究

利用固定床反应器对生物油水溶性组分重整制氢反应进行了考察,研究了温度、吸收剂的加入对反应过程的影响。结果表明,在常压条件下生物油水溶性组分的最佳重整温度为800℃,此时H2体积分数为60%、CO体积分数为10%。加入CO₂吸收剂后,H₂体积分数提高了25%,H₂产率提高了10%。在常压条件下,以CaO作为吸收剂时,最佳的反应温度为600℃,此时H₂体积分数最高可达85%。650℃时CaO对CO₂的吸收能力减弱导致其对生成H₂反应的促进作用急剧降低。     

Gas chromatography method for the characterization of ethanol steam reforming products

Ethanol steam reforming is a promising reaction for producing fuel cell hydrogen. Depending on catalyst and reaction conditions, mixtures of condensable hydrocarbons and organic and inorganic gases are produced. This paper proposes an economic and effective solution for separating and detecting these compounds employing a gas chromatograph equipped with two columns, two 6-way valves, and two detectors.     

镍基整体式催化剂上生物质粗燃气重整调变的特性研究

采用浸渍法制备了Ni基整体式催化剂,考察了不同条件(温度、时间、空速、水蒸气添加等)对催化剂上生物质粗燃气重整反应性能的影响。结果表明,催化剂在较低温度下(≤500 ℃)只具有CO加氢反应活性,随着反应温度的升高粗燃气重整反应逐渐进行,在800 ℃以上,CH₄和C₂转化率均高达95 %以上,CO₂转化率达到92%,但随着反应空速和水蒸气添加量的增加,CH₄和CO₂等转化率呈现缓慢降低的趋势。此外,通过改变水蒸气添加量可对合成气中H₂/CO体积比在0.85~4.00进行较好调节。结合XRD表征发现,Ni基整体式催化剂中Ni°的生成可较好地促进重整反应的进行。     

The potential of proton exchange membrane–based electrolysis technology

Hydrogen is an important chemical feedstock for many industrial applications, and today, more than 95% of this feedstock is generated from fossil fuel sources such as reforming of natural gas. In addition, the production of hydrogen from fossil fuels represents most carbon dioxide emissions from large chemical processes such as ammonia generation. Renewable sources of hydrogen such as hydrogen from water electrolysis need to be driven to similar production costs as methane reforming to address global greenhouse gas emission concerns. Water electrolysis has begun to show scalability to relevant capacities to address this need, but materials and manufacturing advancements need to be made to meet the cost targets. This article describes specific needs for one pathway based on proton exchange membrane electrolysis technology.     

Catalytic Transformation of Oxygenated Organic Compounds into Pure Hydrogen

The continual growth in transportation fuels and more strict environmental legislations have led to immense interest in developing green biomass energy. In this work, a proposed catalytic transformation of oxygenated organic compounds (related to bio-oil) into pure hydrogen was desighed, involving the catalytic reforming of oxygenated organic compounds to hydrogen-rich mixture gas followed by the conversion of CO to CO₂ via the water gas reaction and the removal of CO₂. The optimization of the different reforming catalyst, the reaction conditions as well as various sources of oxygenated organic compounds were investigated in detail. The production of pure hydrogen, with the H₂ content up to 99.96% and the conversion of 97.1%, was achieved by the integrated catalytic transformation. The reaction pathways were addressed based on the investigation of decomposition, catalytic reforming, and the water gas reaction.     

介孔Ni/MgO催化剂催化水蒸气重整生物质油制氢

采用水热法制备了介孔MgO作为催化剂的载体,并制备了介孔Ni/MgO催化剂。利用N_2吸附-脱附、XRD、H_2-TPR等对样品进行表征,并考察了介孔Ni/MgO催化水蒸气重整糠醛、生物质油模型物和两种商用生物质油制氢的活性。结果表明,在介孔Ni/MgO催化剂催化水蒸气重整糠醛制氢反应中,随着反应温度的提高,水蒸气重整糠醛中糠醛的转化率、氢气的产率和氢气的选择性,都呈现递增的趋势。在反应温度提高到600℃时,糠醛的转化率和氢气的产率分别达到94.9%和83.2%。Ni/MgO催化水蒸气重整二组分模拟生物质油,糠醛/乙酸、糠醛/羟基丙酮制氢的反应中,氢气的产率分别达到87.3%和86.8%,均高于水蒸气重整糠醛反应中氢气的产率。由此表明,乙酸或羟基丙酮的存在,提高了模拟生物质油中主要有机物组分糠醛的转化率,并相应地提高了氢气的产率。在水蒸气重整商用生物质油制氢反应中,随着反应物水碳比(S/C(molar ratio)=5、10、15、20、25)的提高,主要有机物的转化率、氢气的产率和选择性呈现出增加的趋势。在水碳比为20时,两种生物质油的主要有机物组分(糠醛、乙酸和羟基丙酮)的转化率均可达90%以上,氢气的产率也达到81.0%以上。由此可知,Ni催化剂对于水蒸气重整商用生物质油也具有较高的催化活性。     

共沉淀镍催化剂用于膜反应器中高碳烃类燃料水蒸气重整反应

 采用共沉淀法制备了NiO/La-Al2O3催化剂,利用低温N2物理吸附、程序升温还原、 H2-O2化学吸附和X射线衍射对催化剂进行了表征,并将该催化剂应用于Pd膜反应器中高碳烃类燃料水蒸气重整反应. 结果表明,催化剂中NiO与载体间存在较强的相互作用. 与常规固定床反应器相比,在膜反应器中,由于高渗透性能的Pd金属复合膜能选择分离氢气,结果氢气产率得到了明显的提高,甲烷的生成得到了有效抑制,并且在接近实用的反应条件下,依然能够得到高的氢气产率和回收率. 高碳烃类燃料水蒸气重整反应制氢的过程可以在一个膜反应器中,利用一种催化剂在反应温度低于823 K的温和条件下实现.