A dense Pd/Ag membrane reactor for methanol steam reforming: Experimental study

This paper focuses on an experimental study of the methanol steam reforming (MSR) reaction. A dense Pd/Ag membrane reactor (MR) has been used, and its behaviour has been compared to the performance of a traditional reactor (TR) packed with the same catalyst type and amount. The parameters investigated are reaction time, temperature, feed ratio and sweep gas flow rate. The few papers dealing with MR applications for the MSR reaction mainly analyse the effect of temperature and pressure on the reaction system. The investigation of new parameters permitted to better understand how the fluid-dynamics of the MR influences the hydrogen separation effect on methanol conversion and product selectivity. The comparison between MR and TR in terms of methanol conversion shows that the MR gives a higher performance than the TR at each operating condition investigated. Concerning hydrogen production, the experiments have shown that the overall selectivity towards hydrogen is identical for both MR and TR. However, the MR produces a free-CO hydrogen stream, which could be useful for direct application in proton exchange membrane fuel cells. A comparison, in terms of methanol conversion versus temperature, with literature data is also included.     

Poly-dimethylsiloxane (PDMS) based micro-reactors for steam reforming of methanol

A miniaturized methanol steam reformer with a serpentine type of micro-channels was developed based on poly-dimethylsiloxane (PDMS) material. This way of fabricating micro-hydrogen generator is very simple and inexpensive. The volume of a PDMS micro-reformer is less than 10 cm³. The catalyst used was a commercial Cu/ZnO/Al₂O₃ reforming catalyst from Johnson Matthey. The Cu/ZnO/Al₂O₃ reforming catalyst particles of mean diameter 50-70 μm was packed into the micro-channels by injecting water based suspension of catalyst particles at the inlet point. The miniaturized PDMS micro-reformer was operated successfully in the operating temperatures of 180-240 °C and 15%-75% molar methanol conversion was achieved in this temperature range for WHSV of 2.1-4.2 h⁻¹. It was not possible to operate the micro-reformer made by pure PDMS at temperature beyond 240 °C. Hybrid type of micro-reformer was fabricated by mixing PDMS and silica powder which allowed the operating temperature around 300 °C. The complete conversion (99.5%) of methanol was achieved at 280 °C in this case. The maximum reformate gas flow rate was 30 ml/min which can produce 1 W power at 0.6 V assuming hydrogen utilization of 60%.     

Performance of microchannel reactor combined with combustor for methanol steam reforming

The microchannel reactor with combustor for methanol steam reforming was fabricated to produce hydrogen for onboard proton exchange membrane (PEM) fuel cell device. A commercial copper-containing catalyst (Cu/ZnO/Al₂O₃) and Pt/ZrO₂ were used as a catalyst for methanol steam reforming and combustion reaction, respectively. It was found that catalyst layer with zirconia sol solution in microchannel showed no crack on the surface of catalyst layer and an excellent adherence to stainless steel microchannel even after reaction. The temperature of combustor could be controlled between 200 and 300 °C depending on the methanol feed rate. The hydrogen flow of 3.9 l h⁻¹ hydrogen was obtained with the reforming feed flow rate of 3.65 ml h⁻¹ at 270 °C.     

Characterization of CuMn-spinel catalyst for methanol steam reforming

CuMn-spinel oxide (CuMn(S)) and non-spinel CuMn (CuMn(NS)) oxide have been obtained by calcining the same precursor at 900 °C and 300 °C, respectively. CuMn(S) was composed of Cu_1.5Mn_1.5O₄ spinel and Mn₃O₄, while CuMn(NS) consisted of CuO and Mn₃O₄. XRD, EXAFS, and TEM measurements of the samples reduced in hydrogen revealed that both CuMn(S) and CuMn(NS) were reduced to Cu metal dispersed on MnO and that the particle size of Cu metal from the CuMn(S) was smaller than that from CuMn(NS). In methanol steam reforming, the spinel derived catalyst showed higher activity than the non-spinel due to the higher dispersion of the Cu metal.     

Hydrogen production from methanol by oxidative steam reforming carried out in a membrane reactor

The aim of this work is to study from an experimental point of view the oxidative steam reforming of methanol by investigating the behaviour of a dense Pd/Ag membrane reactor (MR) in terms of methanol conversion as well as hydrogen production. The main parameters considered are the operating temperature and the O₂/CH₃OH feed ratio. This is a pioneer work in the application of MR to this kind of reaction, whose goal should be to produce a CO-free hydrogen stream suitable for hydrogen fuel cell applications. The experimental results show that the MR gives methanol conversions higher than traditional reactors (TRs) at each temperature investigated, confirming the good potential of the membrane reactor device for this interesting reaction system.     

RuAg/TiO2-C催化剂的制备及对甲醇的电催化氧化性能

采用改性溶胶凝胶法和水热合成法制备了掺C多孔纳米TiO2,并以其为载体制备了一种RuAg/TiO2-C甲醇催化剂。采用X射线衍射（XRD）、透射电镜（TEM）、X射线能谱（EDS）和X射线光电子能谱（XPS）等对催化剂进行了表征,测定了其对甲醇的电催化氧化性能。实验结果表明,RuAg的负载和C的掺杂能提高TiO2对甲醇的电催化性能,RuAg/TiO2-C对甲醇电催化的循环伏安曲线中未见甲醇氧化中间产物的氧化峰,0.544 V处有一个较大的甲醇氧化峰,其峰电流密度5.8 mA/cm2,RuAg/TiO2-C比商用PtRu/C催化剂具有更高的催化活性和抗毒性,RuAg合金的负载以及RuAg合金与掺C多孔纳米TiO2载体之间较强的相互作用是其对甲醇催化性能提高的主要因素。     

Hydrogen production by methanol steam reforming carried out in membrane reactor on Cu/Zn/Mg-based catalyst

The methanol steam reforming (MSR) reaction was studied by using both a dense Pd-Ag membrane reactor (MR) and a fixed bed reactor (FBR). Both the FBR and the MR were packed with a new catalyst based on CuOAl₂O₃ZnOMgO, having an upper temperature limit of around 350 °C. A constant sweep gas flow rate in counter-current mode was used in MR and the experiments were carried out by varying the water/methanol feed molar ratio in the range 3/1–9/1 and the reaction temperature in the range 250–300 °C. The catalyst shows high activity and selectivity towards the CO₂ and the H₂ formation in the temperature range investigated. Under the same operative conditions, the MR shows higher conversions than FBR and, in particular, at 300 °C and H₂O/CH₃OH molar ratio higher than 5/1 the MR shows complete methanol conversion.     

NC501型甲醇合成催化剂使用小结

介绍了NC 5 0 1型甲醇合成催化剂的使用情况 ,认为NC 5 0 1具有以下特点 :( 1)升温还原平稳 ,低温出水集中 ;( 2 )低温活性好 ;( 3)甲醇产量明显提高 ;( 4)具有较好的选择性及抗毒性等。并就催化剂的使用说明及原料气中CO2 的含量等提出了建议     

甲醇水蒸汽重整制氢反应的热力学分析

针对甲醇水蒸汽重整制氢反应体系,通过理论计算研究了化学平衡常数随温度的变化规律,指出该反应适宜的反应温度。选取自行开发的CuZnZrAlO催化剂作为研究对象,比较了反应体系中理论平衡组成和实际组成之间的差别,研究了体系中两个独立反应——甲醇分解和水蒸汽变换的反应进度受温度影响的敏感度。通过比较实际反应性能和理论平衡极限的差别,为CuZnZrAlO催化剂的进一步改进提供了研究方向。     

催化活性分布对甲醇水蒸气重整制氢的影响

为了强化微通道中甲醇水蒸气重整制氢,考察了催化表面活性分布对该反应过程的影响。利用计算流体力学软件FLUENT中的通用有限速率模型对微通道中甲醇水蒸气重整进行了二维数值研究。计算表明,在相同的反应条件下,通过微通道壁面上催化活性的合理分布可以提高反应器出口甲醇的转化率,这一效果在低进口温度和高速度下更为明显,在进口温度为453 K、进口速度为1.0 m/s下转化率最大提高46%。合理的活性分布应是进口处活性较低,沿着反应通道活性逐渐增加。这种催化活性分布还可降低反应通道中的冷点温差。     

Methanol steam reforming over paper-like composites of Cu/ZnO catalyst and ceramic fiber

Copper–zinc oxide catalyst powders were successfully prepared into paper-like composites, called catalyst paper in this study, using ceramic fibers as the carrier matrix of the catalyst. A papermaking technique with a dual polyelectrolyte retention system was used. Catalyst particles were supported on the ceramic fiber networks tailored in the catalyst paper having various types of pores. Pieces of catalyst paper were subjected to methanol steam reforming (MSR) to produce hydrogen gas for fuel cell applications. They demonstrated a higher performance for methanol conversion and hydrogen production in the MSR reaction than commercial Cu/ZnO catalyst pellets, exhibiting an efficacy equivalent to that of the original catalyst powders. The concentration of carbon monoxide, which acts as a catalytic poison for fuel electrode catalysts, decreased remarkably, without any carbon monoxide reduction system. Moreover, the porous structure of catalyst paper influenced the MSR efficiency. It was assumed that the macropores ca. 20 μm in diameter greatly contributed to the MSR performance, rather than the mesopores on the catalyst surfaces. Thus, the porous, flexible and easy-to-handle catalyst paper is a promising material for practical MSR applications.     

Preparation and characterization of Ir-based catalysts on metallic supports for high-temperature steam reforming of methanol

Ir-based catalysts on heat-resisting foil supports with different washcoats were investigated for hydrogen production by high-temperature steam reforming of methanol. Al₂O₃, Ce_0.8Zr_0.2O₂–Al₂O₃, Ce_0.8Zr_0.2O₂/Al₂O₃ and Ce_0.8Zr_0.2O₂ coatings were prepared on the metallic supports and iridium was deposited on them as the active component. The samples were characterized by X-ray powder diffraction (XRD), ultrasonic vibration test, scanning electron microscope (SEM) and temperature-programmed reduction (TPR). The performance of the catalysts for steam reforming of methanol was evaluated with a fixed-bed reactor. It was found that the phase structure, the shape of the surface particles and the coating adherence were different from each other for the four kinds of coatings. The activities, selectivities and stabilities of these Ir-based catalysts on metallic supports were compared to select the optimal one for use in high-temperature methanol steam reforming. The results indicated that the Ir/Ce_0.8Zr_0.2O₂/Al₂O₃/FeCrAl catalyst showed better performance than the other catalysts, which is a promising candidate for hydrogen production via the methanol steam reforming process in Pd membrane reactors.     

Steady-state isotopic transient kinetic analysis of steam reforming of methanol over Cu-based catalysts

Mechanistic aspects of steam reforming of methanol were studied via steady-state isotopic transient kinetic analysis over three copper-based catalysts, namely combustion-synthesized Cu-Ce-O and Cu-Mn-O, and commercial Cu-ZnO-Al₂O₃. The “C-path” and “O-path” for the production of CO₂ via steam reforming of methanol was analysed with the following step changes in the feed: ¹²CH₃OH/H₂O/Ar/He → ¹³CH₃OH/H₂O/He and CH₃OH/H₂¹⁶O/Ar/He → CH₃OH/H₂¹⁶O/H₂¹⁸O/He. The presence of CH₃¹⁸OH in the products after the switch to ¹⁸O-labeled water indicates that a major path of the reaction is the one involving a methyl formate intermediate. This appears to be the main path over the Cu-Mn-O catalyst, while parallel paths via dioxomethylene and methyl formate intermediates appear to be operative over Cu-Ce-O and Cu-ZnO-Al₂O₃ catalysts.     

Pt-rich shell coated Ni nanoparticles as catalysts for methanol electro-oxidation in alkaline media

The Pt-rich shell coated Ni nanoparticles in size of 8.9–12.1 nm were synthesized by chemical deposition via successive reduction of NiCl₂ and H₂PtCl₆, respectively, in an ethylene glycol solution and characterized by TEM, XPS, ICP–AES, and XRD techniques. The electrochemical evaluation showed that as-prepared core–shell structural nanoparticles, as a catalyst for methanol electro-oxidation in alkaline media, not only exhibited better catalytic activity and resistance to carbonaceous intermediate poison than pure solid Pt nanoparticles but also decreased wastage of expensive Pt.     

仿蜂巢微通道分叉结构的甲醇重整制氢

针对甲醇蒸汽的微通道重整催化反应过程,建立了三维稳态多组分传输反应模型;利用数值模拟分析,分别研究了平行阵列微通道和仿蜂巢分叉微通道在Zn_Cr/CeO₂/ZrO₂催化剂下的反应情况。通过双速率模型考察这两种流道中操作条件对甲醇蒸汽重整制氢输运规律的影响,发现这两种微通道反应器均可促进甲醇转化率和氢气产率的提高。与常规平行微通道的比较发现,仿蜂巢分叉微通道内反应气流动所需的泵功较小;在相同的加热面积下所能吸收的热量更大,而且更有利于反应器内温度的均匀分布,从而提高甲醇的转化率、减小出口CO的含量。研究结果表明,仿蜂巢分叉微通道结构具有较好的重整制氢综合性能,并可改善氢气产出的品质。     

A comparison of auto-thermal and conventional methanol synthesis reactor in the presence of catalyst deactivation

This study proposed a one-dimensional dynamic plug flow model to analyze and compare the performance of an auto-thermal and a conversional methanol synthesis reactor in the presence of catalyst deactivation. An auto-thermal two-stage industrial methanol reactor type is a system with two catalyst beds instead of one single catalyst bed. In the first catalyst bed, the synthesis gas is partly converted to methanol in a water-cooled reactor. In the second bed which is a gas-cooled reactor, the reaction heat is used to preheat the feed gas to the first bed. To analyze the effect of important control variables on the rector performance, steady state and dynamic simulations are utilized to investigate effect of operating parameters on the performance of reactors. The simulation results show that there is a favorable profile of temperature along the two-stage auto-thermal reactor type in comparison with conventional single stage reactor type. In this way the catalysts are exposed to less extreme temperatures and, catalyst deactivation via sintering is reduced. Overall, this study resulted in beneficial information about the performance of the reactor over catalyst life-time.     

Hydrogen production by oxidative methanol reforming with various oxidants over Cu-based catalysts

In order to improve the start-up property of a small hydrogen producer with a micro methanol reformer, oxidative methanol reforming (OMR) with various oxidants over copper-based catalysts was examined. The addition of Fe to a Cu/ZnO/Al₂O₃ catalyst resulted in higher catalyst durability, with a slight improvement in catalytic activity, for OMR with air. However, the addition of larger amounts of Fe inhibited further improvement of catalytic performance, possibly due to the formation of less active CuFe₂O₄ spinel in the catalyst. The production of hydrogen by OMR with hydrogen peroxide as an alternative oxidant, which has the potential to provide concentrated hydrogen without nitrogen dilution, was also considered. It was found that hydrogen peroxide is an effective oxidant for OMR over copper-based catalysts due to its ability to suppress CO formation and its improving effect on methanol conversion.     

Reactor design limitations for the steam reforming of methanol

In this paper the limiting mechanisms in the methanol-steam reformation process are analyzed theoretically and compared experimentally as to determine each contribution and limitation to the overall process. Experimental data from steam reformers are presented and analyzed. Models of each mechanism are provided to quantify theoretical times necessary for each process to occur. While the models in this paper are not precise representations of all steam reforming processes, the models do provide enough evidence to conclude that heat transfer is the dominant limiting mechanism in methanol-steam reformation. Further studies quantifying the experimental effects of heat transfer should be pursued with the ultimate goal of properly sizing steam reformers.     

甲醇合成催化剂技术的发展与展望

总结了近年来国内外甲醇合成催化剂技术的发展情况,并对今后的研究趋向作了展望。