Hydrogen production from oxidative steam reforming of ethanol in a palladium-silver alloy composite membrane reactor

In this investigation, we studied the oxidative steam reforming reaction of ethanol in a Pd-Ag/PSS membrane reactor for the production of high purity hydrogen. Palladium and silver were deposited on porous stainless steel (PSS) tube via the sequential electroless plating procedure with an overall film thickness of 20 μm and Pd/Ag weight ratio of 78/22. An ethanol-water mixture (n_water/n_ethanol = 1 or 3) and oxygen (n_oxygen/n_ethanol = 0.2, 0.7 or 1.0) were fed concurrently into the membrane reactor packed with Zn-Cu commercial catalyst (MDC-3). The reaction temperatures were set at 593-723 K and the pressures at 3-10 atm. The hydrogen flux in the permeation side increased proportionately with increasing pressure; however, it reduced slightly when increasing oxygen input. This is probably due to the fast oxidation reaction that consumes hydrogen before the onset of the steam reforming reaction. The effect of oxygen plays a vital role on the ethanol oxidation steam reforming reaction, especially for a Pd-Ag membrane reactor in which a higher flux of hydrogen is required. The selectivity of CO₂ increased with increasing flow rate of oxygen, while the selectivity of CO remained almost the same.     

Catalytic monoliths for ethanol steam reforming

Cordierite monoliths coated with Co/ZnO catalysts were prepared by washcoating, urea, and sol–gel techniques and characterized by confocal microscopy, scanning electron microscopy (SEM), transmission electron microscopy, X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR), and adherence tests. The performance of the catalytic monoliths for practical application in the production of hydrogen through ethanol steam reforming (ESR) and water gas shift (WGS) reactions was evaluated. Monoliths prepared by the urea method exhibited excellent dispersion and adherence of catalyst coatings and performed better for the reforming of ethanol. 5.6 mol H₂/mol C₂H₅OH were obtained from a C₂H₅OH:H₂O = 1:6 gaseous mixture at 723 K and 0.33 mL min⁻¹ of C₂H₅OH. Under these conditions and total ethanol conversion the composition of the effluent stream was 73.9% H₂, 23.7% CO₂, 1.2% CO, and 1.0% CH₄. The amount of CO was kept low due to the activity of monoliths for the WGS reaction under ethanol steam reforming conditions.     

负载型金属催化剂在乙醇水蒸气重整制氢中的应用

系统地阐述了近年来对乙醇水蒸气重整制氢催化剂的研究进展;对影响催化剂性能的因素及对策进行了分析与讨论;展望了乙醇水蒸气制氢催化剂的研究方向.     

Oxidative steam reforming of ethanol over PtRu/ZrO2 catalysts modified with sodium and magnesium

This paper reports the catalytic performance of a PtRu/ZrO₂ catalyst modified with Na and Mg in an oxidative steam reforming of ethanol (OSRE) reaction tested in the temperature range of 300–400 °C. The results show that the PtRuMg₁/ZrO₂ catalyst requires higher temperatures (T_R ~ 400 °C) to achieve complete conversion than either the PtRuNa₁/ZrO₂ or PtRu/ZrO₂ catalysts (T_R ~ 300 °C). Also, an apparent coke deposit is found on the PtRuMg₁/ZrO₂ catalyst. The preferential PtRuNa₁/ZrO₂ catalyst shows active at temperatures as low as 300 °C and produces less CO (< 0.2%) at temperatures lower than 340 °C.     

Production of hydrogen for fuel cells by steam reforming of ethanol over supported noble metal catalysts

The catalytic performance of supported noble metal catalysts for the steam reforming (SR) of ethanol has been investigated in the temperature range of 600–850 °C with respect to the nature of the active metallic phase (Rh, Ru, Pt, Pd), the nature of the support (Al₂O₃, MgO, TiO₂) and the metal loading (0–5 wt.%). It is found that for low-loaded catalysts, Rh is significantly more active and selective toward hydrogen formation compared to Ru, Pt and Pd, which show a similar behavior. The catalytic performance of Rh and, particularly, Ru is significantly improved with increasing metal loading, leading to higher ethanol conversions and hydrogen selectivities at given reaction temperatures. The catalytic activity and selectivity of high-loaded Ru catalysts is comparable to that of Rh and, therefore, ruthenium was further investigated as a less costly alternative. It was found that, under certain reaction conditions, the 5% Ru/Al₂O₃ catalyst is able to completely convert ethanol with selectivities toward hydrogen above 95%, the only byproduct being methane. Long-term tests conducted under severe conditions showed that the catalyst is acceptably stable and could be a good candidate for the production of hydrogen by steam reforming of ethanol for fuel cell applications.     

Catalytic performance and characterization of Pt-Ni bimetallic catalysts for oxidative steam reforming of methane

Effects of methane oxygen mixture addition to steam reforming of methane and subsequent removal of the methane oxygen mixture from the oxidative steam reforming of methane on catalytic performance were investigated using monometallic Ni and Pt catalysts and two Pt-Ni bimetallic catalysts. Hysteresis with respect to the addition and removal of the methane oxygen mixture was observed clearly on a Pt-Ni bimetallic catalyst prepared by co-impregnation method and the Ni catalyst. In contrast, no hysteresis was observed for a Pt-Ni catalyst that was prepared by sequential impregnation method. Combined with characterization results obtained using EXAFS analysis and FTIR of CO adsorption, Pt-Ni catalyst was prepared by sequential impregnation is formed Pt-Ni alloy particles, where Pt atoms are segregated on the surface, enhances the reducibility of Ni drastically and this is related to the behavior without hysteresis.     

Ni catalysts with Mo promoter for methane steam reforming

NiO/Al₂O₃ catalyst precursors were prepared by simultaneous precipitation, in a Ni:Al molar ratio of 3:1, promoted with Mo oxide (0.05, 0.5, 1.0 and 2.0 wt%). The solids were characterized by adsorption of N₂, XRD, TPR, Raman spectroscopy and XPS, then activated by H₂ reduction and tested for the catalytic activity in methane steam reforming.The characterization results showed the presence of NiO and Ni₂AlO₄ in the bulk and Ni₂AlO₄ and/or Ni₂O₃ and at the surface of the samples.In the catalytic tests, high stability was observed with a reaction feed of 4:1 steam/methane. However, at a steam/methane ratio of 2:1, only the catalyst with 0.05% Mo remained stable throughout the 500 min of the test.The addition of Mo to Ni catalysts may have a synergistic effect, probably as a result of electron transfer from the molybdenum to the nickel, increasing the electron density of the catalytic site and hence the catalytic activity.     

Synthesis gas production by steam reforming of ethanol

A two-layer fixed-bed catalytic reactor for syngas production by steam reforming of ethanol has been proposed. In the reactor, ethanol is first converted to a mixture of methane, carbon oxides and hydrogen over a Pd-based catalyst and then this mixture is converted to syngas over a Ni-based catalyst for methane steam reforming. It has been shown that the use of the two-layer fixed-bed reactor prevents coke formation and provides the syngas yield closed to equilibrium.     

Novel circulating fast fluidized-bed membrane reformer for efficient production of hydrogen from steam reforming of methane

The coupling of steam reforming and oxidative reforming of methane for the efficient production of hydrogen is investigated over Ni/Al₂O₃ catalyst in a novel circulating fast fluidized-bed membrane reformer (CFFBMR) using a rigorous mathematical model. The removal of product hydrogen using palladium hydrogen membranes “breaks” the thermodynamic equilibrium barrier exists among the reversible reactions. Oxygen can be introduced into the adiabatic CFFBMR for oxidative reforming by direct oxygen (or air) feed and through dense perovskite oxygen membranes. The simulations show that high productivity of hydrogen can be obtained in the CFFBMR. The combination of these two different processes does not only enhance the hydrogen productivity but also save the energy due to the exothermicity of the oxidative reforming. Based on the preliminary investigations, four parameters (number of hydrogen membranes, number of oxygen membranes, direct oxygen feed rate and steam-to-carbon feed ratio) are carefully chosen as main variables for the process optimization. The optimized result shows that the hydrogen productivity (moles of hydrogen produced per hour per m³ of reactor) in the novel CFFBMR is about 8.2 times higher than that in typical industrial fixed-bed steam reformers.     

国内外蒸汽转化制氢催化剂及工艺进展

本文分别对烃类蒸汽转化制氢技术中涉及的原料、工艺、设备及催化剂等方面的国内外进展进行了讨论，评述了烃类蒸汽转化制氢技术的发展趋势并提出有关建议。     

Co/CeO2-ZrO2 catalysts prepared by impregnation and coprecipitation for ethanol steam reforming

Co/CeO₂-ZrO₂ catalysts for the ethanol steam reforming were prepared by wet incipient impregnation and coprecipitation methods. These catalysts were characterized by nitrogen adsorption, TEM-EDX, XRD, H₂-TPR, and CO chemisorption techniques. It was found that the catalyst reducibility was influenced by the preparation methods; catalysts with different reduction behaviors in the pre-reduction showed different catalytic activities toward hydrogen production. The H₂-TPR studies suggested the presence of metal–support interactions in Co/CeO₂-ZrO₂ catalysts during their hydrogen pre-reduction, a necessary treatment process for catalysts activation. These interactions were influenced by the preparation methods, and the impregnation method is a favorable method to induce a proper metal–support effect that allows only partial reduction of the cobalt species and leads to a superior catalytic activity for the hydrogen production through ethanol steam reforming. At 450 °C, the impregnated catalyst gives a hydrogen production rate of 147.3 mmol/g-s at a WHSV of 6.3 h⁻¹ (ethanol) and a steam-to-carbon ratio of 6.5.     

Carbon formation and its influence on ethanol steam reforming over Ni/Al2O3 catalysts

Ethanol steam reforming was studied over Ni/Al₂O₃ catalysts. The effect of support (- and γ-Al₂O₃), metal loading and a comparison between conventional H₂ reduction with an activation method employing a CH₄/O₂ mixture was investigated. The properties of catalysts were studied by N₂ physisorption, X-ray diffraction (XRD) and temperature programmed reduction (TPR). After activity tests, the catalysts were analyzed by scanning electron microscopy (SEM) and thermogravimetric analysis (TG/DTA). Ni supported on γ-Al₂O₃ was more active for H₂ production than the catalyst supported on -Al₂O₃. Metal loading did not affect the catalytic performance. The alternative activation method with CH₄/O₂ mixture affected differently the activity and stability of the Ni/γ-Al₂O₃ and the Ni/-Al₂O₃ catalyst. This activation method increased significantly the stability of Ni/-Al₂O₃ compared to H₂ reduction. SEM and TG/DTA analysis indicate the formation of filamentous carbon during the CH₄/O₂ activation step, which is associated with the increasing catalyst activity and stability. The effect of temperature on the type of carbon formed was investigated; indicating that filamentous coke increased activity while encapsulating coke promoted deactivation. A discussion about carbon formation and the influence on the activity is presented.     

Reaction path of ethanol and acetic acid steam reforming over Ni–Zn–Al catalysts. Flow reactor studies

Ethanol steam reforming (ESR) experiments have been performed in dilute conditions over a NiZnAl catalyst. Experiments have been performed by varying catalyst surface area, reactants flow rate, contact time, reactants feed composition and temperature. Acetic acid steam reforming experiments have also been performed. The data suggest that adsorbed acetaldehyde and acetic acid play an important role as intermediates of ESR, while also acetone may have a role in the ESR reaction. The key step for high hydrogen yield during ESR is represented by the evolution of acetate species, either towards decomposition giving rise to methane + CO_x, or to steam reforming to CO₂ and H₂. At high temperature hydrogen production depends on approaching methane steam reforming and reverse water gas shift equilibria. Ethylene end dimethylether are parallel products found at low conversion. With excess water acetaldehyde is not found among the products, and hydrogen yields as high as 95% have been obtained at 853 K.     

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.     

Catalytic performance and QXAFS analysis of Ni catalysts modified with Pd for oxidative steam reforming of methane

Pd–Ni bimetallic catalysts prepared by co-impregnation and sequential impregnation methods were compared in the catalytic performance in oxidative steam reforming of methane. The sequential impregnation was more effective to the suppression of hot spot formation. According to the structural analysis by in situ quick-scanning X-ray absorption fine structure (QXAFS) during the temperature programmed reduction, the sequential impregnation method gave the bimetallic particles with higher Pd surface composition because of the low possibility of the Pd–Ni bond formation. Higher surface composition of Pd with higher reducibility than Ni is connected to the enhancement of the catalyst reducibility and the suppression of the hot spot formation.     

Pd/ZnO催化剂上甲醇水蒸气重整制氢

研究了并流共沉淀法制备的Pd/ZnO催化剂上的甲醇水蒸气重整制氢反应.考察了钯含量、还原温度、反应温度、重时空速（WHSV）和水-甲醇摩尔比（水醇比）对反应的影响.研究结果表明,当钯质量分数为15.9%,反应温度为523～573 K,还原温度为523～573 K,水醇比为1.0～1.2,WHSV=17.2 h^-1时,反应具有较好的CH3OH转化率、CO₂选择性、H₂产率及较低的出口CO摩尔分数.与铜基催化剂相比,Pd/ZnO催化剂表现出较好的稳定性.     

Enhanced oxygen mobility and reactivity for ethanol steam reforming

This article describes a strategy for increasing oxygen storage capacity (OSC) of ethanol steam reforming (ESR) catalysts. Sintering and carbon deposition are major defects of nickel‐based catalysts for ESR; tuning oxygen mobility (OM) of CeO₂‐based supports can overcome these drawbacks and promote H₂ production. We have successfully increased OSC and OM by adding Mg into the lattice of Ni/CeO₂ to promote H₂ production in ESR. The insertion of Mg into the CeO₂ lattice efficiently promotes the reduction of Ce⁴⁺ according to X‐ray powder diffraction (XRD) and temperature‐programmed reduction (TPR) analysis. Mg‐modified Ni/CeO₂ catalysts have larger OSC and smaller nickel crystallite size compared with bare Ni/CeO₂. The optimal Mg addition is 7 mol % (Ni/7MgCe) with the best OM. We also present evidence indicating that Mg addition significantly promotes ethanol conversion and H₂ production in ESR, and that Ni/7MgCe yields the best performance due to the high OM of the support. These Mg‐modified catalysts also produce less carbon deposition compared with Ni/CeO₂, and the amount of deposited carbon decreases with increasing Mg addition. Ni/7MgCe has the best resistance to carbon deposition owing to the excellent OM. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

Yolk-shell structured Pt-CeO2@Ni-SiO2 as an efficient catalyst for enhanced hydrogen production from ethanol steam reforming

A novel Pt-CeO₂@Ni-SiO₂ yolk-shell catalyst was fabricated through modified Stöber method and was applied to the ethanol steam reforming reaction. The catalyst structure was characterized by scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectrometry, X-ray diffraction, nitrogen adsorption-desorption and X-ray photoelectron spectroscopy. Compared with the mechanically mixed catalyst, the yolk-shell catalyst exhibited excellent catalytic performance and stability in ethanol steam reforming. The selection of hydrogen reached as high as 66%, and the conversion reached nearly 100% at 400 °C for 28 h.     

Z402/Z405G高抗炭性烃类蒸汽转化催化剂的性能和工业应用

介绍了高抗炭性烃类蒸汽转化催化剂Z402/Z405G的抗炭机理、催化性能、还原条件及使用方法,并报道了其工业应用实例。