Production of hydrogen by steam reforming of bio-oil over Ni/Al2O3 catalysts: Effect of addition of promoter and preparation procedure

Catalytic steam reforming of bio-oil was investigated in a fixed bed tubular reactor for production of hydrogen. Two series of nickel/alumina (Ni/Al₂O₃) supported catalysts promoted with ruthenium (Ru) and magnesium (Mg) were prepared. Each catalyst of the first series (Ru–Ni/Al₂O₃) was prepared by co-impregnation of nickel and ruthenium on alumina. They were examined to investigate the effect of adding ruthenium on the performance of the catalysts for hydrogen production. The effect of the temperature, the most effective parameter in the steam reforming of bio-oil, on the activity of the catalysts was also investigated. Each catalyst of the second series (Ni–MgO/Al₂O₃) was prepared by consecutive impregnation using various preparation procedures. They were tested to determine the effect of adding magnesium as well as the effect of the preparation procedure on the outlet gas concentrations. It was shown that in both series, the catalysts were more efficient in hydrogen production as well as carbon conversion than Ni/Al₂O₃ catalysts. The highest hydrogen yield was 85% which was achieved over Ru–Ni/Al₂O₃ at 950 °C. It was also found that the effect of adding a small amount of ruthenium was superior to that of nickel on the yield of hydrogen when the nickel content was equal to or greater than 10.7%.     

Steam reforming of methanol using Cu-ZnO catalysts supported on nanoparticle alumina

Methanol steam reforming was studied over several catalysts made by deposition of copper and zinc precursors onto nanoparticle alumina. The results were compared to those of a commercially available copper, zinc oxide and alumina catalyst. Temperature programmed reduction, BET surface area measurements, and N₂O decomposition were used to characterize the catalyst surfaces. XRD was used to study the bulk structure of the catalysts, and XPS was used to determine the chemical states of the surface species. The nanoparticle-supported catalysts achieved similar conversions as the commercial reference catalyst but at slightly higher temperatures. However, the nanoparticle-supported catalysts also exhibited a significantly lower CO selectivity at a given temperature and space time than the reference catalyst. Furthermore, the turnover frequencies of the nanoparticle-supported catalysts were higher than that of the commercial catalyst, which means that the activity of the surface copper is higher. It was determined that high alumina concentrations ultimately decrease catalytic activity as well as promote undesirable CH₂O formation. The lower catalytic activity may be due to strong Cu-Al₂O₃ interactions, which result in Cu species which are not easily reduced. Furthermore, the acidity of the alumina support appears to promote CH₂O formation, which at low Cu concentrations is not reformed to CO₂ and H₂. The CO levels present in this study are above what can be explained by the reverse water-gas-shift (WGS) reaction. While coking is not a significant deactivation pathway, migration of ZnO to the surface of the catalyst (or of Cu to the bulk of the catalyst) does explain the permanent loss of catalytic activity. Cu₂O is present on the spent nanoparticle catalysts and it is likely that the Cu⁺/Cu⁰ ratio is of importance both for the catalytic activity and the CO selectivity.     

生物油水蒸气催化重整制氢研究进展

氢气作为重要的清洁能源和化工原料,目前主要来源于化石燃料,而生物质经快速热解制得生物油用于水蒸气催化重整制氢被认为是一种高效、环保、经济的可再生能源制氢途径。本文首先综述了近年来生物油水蒸气催化重整制氢相关反应原料;然后重点讨论了生物油水蒸气催化重整反应催化剂研究近况;总结了生物油水蒸气重整反应机理与动力学分析;最后列举了重整反应器等方面的研究进展。相比于生物油,生物油模型化合物因结构简单、转化率与氢气收率高,得到广泛研究;以Ni为代表的活性金属组分催化活性高,金属间协同作用强;不同类型的载体可增强催化剂的稳定性,碱性载体还可吸收CO₂、提高催化剂抗积炭、防烧结等方面的性能;不同结构的反应器在性能方面表现各异,主要以固定床反应器为主。研制高活性、稳定性强的催化剂,提高重整反应的循环稳定性,并总结最符合动力学规律的反应机理,以及研发高效的反应器是今后生物油水蒸气催化重整制氢研究的重点。     

Influence of molybdenum and tungsten additives on the properties of nickel steam reforming catalysts

An introduction of small amounts of molybdenum and tungsten compounds into the nickel catalyst of the steam reforming of methane considerably reduces the detrimental effect of carbon deposit formation, while entailing no change in the catalyst activity.     

Hydrogen production by oxidative steam reforming of methanol using ceria promoted copper–alumina catalysts

The performance of different Cu/CeO₂/Al₂O₃ catalysts of varying compositions is investigated for the oxidative steam reforming of methanol (OSRM) in order to produce the hydrogen selectively for polymer electrolyte membrane (PEM) fuel cell applications. All the catalysts were prepared by co-precipitation method and characterized for their surface area, pore volume and oxidation–reduction behavior. The effect of various operating parameters studied are as follows: reaction temperature (200–300 °C), contact-time (W/F = 3–15 kg_cat s mol^− 1) and oxygen to methanol (O/M) molar ratio (0–0.5). The steam to methanol (S/M) molar ratio = 1.5 and pressure = 1 atm were kept constant. Among all the catalysts studied, catalyst Cu–Ce–Al:30–20–50 exhibited 100% methanol conversion and 179 mmol s^− 1 kg_cat^− 1 hydrogen production rate at 280 °C with carbon monoxide formation as low as 0.19%. The high catalytic activity and hydrogen selectivity shown by ceria promoted Cu/Al₂O₃ catalysts is attributed to the improved specific surface area, dispersion and reducibility of copper which were confirmed by characterizing the catalysts through temperature programmed reduction (TPR), CO chemisorption, X-ray diffraction (XRD) and N₂ adsorption–desorption studies. Reaction parameters were optimized in order to produce hydrogen with carbon monoxide formation as low as possible. The time-on-stream stability test showed that the Cu/CeO₂/Al₂O₃ catalysts were quite stable.     

Stable carbon dioxide reforming of methane over modified Ni/Al2O3 catalysts

CO₂ reforming of methane was studied over modified Ni/Al₂O₃ catalysts. The metal modifiers were Co, Cu, Zr, Mn, Mo, Ti, Ag and Sn. Relative to unmodified Ni/Al₂O₃, catalysts modified with Co, Cu and Zr showed slightly improved activity, while other promoters reduced the activity of CO₂ reforming. Mn-promoted catalyst showed a remarkable reduction in coke deposition, while entailing only a small reduction in catalytic activity compared to unmodified catalyst. The catalysts prepared at high calcination temperatures showed higher activity than those prepared at low calcination temperature. The Mn-promoted catalyst showed very low coke deposition even in the absence of diluent gas and the activity changed only slightly during 100 h operation. This revised version was published online in July 2006 with corrections to the Cover Date.     

Hydrogen production via catalytic steam reforming of fast pyrolysis bio-oil in a two-stage fixed bed reactor system

Hydrogen production was prepared via catalytic steam reforming of fast pyrolysis bio-oil in a two-stage fixed bed reactor system. Low-cost catalyst dolomite was chosen for the primary steam reforming of bio-oil in consideration of the unavoidable deactivation caused by direct contact of metal catalyst and bio-oil itself. Nickel-based catalyst Ni/MgO was used in the second stage to increase the purity and the yield of desirable gas product further. Influential parameters such as temperature, steam to carbon ratio (S/C, S/CH₄), and material space velocity (W_BHSV, GHSV) both for the first and the second reaction stages on gas product yield, carbon selectivity of gas product, CH₄ conversion as well as purity of desirable gas product were investigated. High temperature (> 850 °C) and high S/C (> 12) are necessary for efficient conversion of bio-oil to desirable gas product in the first steam reforming stage. Low W_BHSV favors the increase of any gas product yield at any selected temperature and the overall conversion of bio-oil to gas product increases accordingly. Nickel-based catalyst Ni/MgO is effective in purification stage and 100% conversion of CH₄ can be obtained under the conditions of S/CH₄ no less than 2 and temperature no less than 800 °C. Low GHSV favors the CH₄ conversion and the maximum CH₄ conversion 100%, desirable gas product purity 100%, and potential hydrogen yield 81.1% can be obtained at 800 °C provided that GHSV is no more than 3600 h^− 1. Carbon deposition behaviors in one-stage reactor prove that the steam reforming of crude bio-oil in a two-stage fixed bed reaction system is necessary and significant.     

Characterization of Sn doped Ni/Al2O3 steam reforming catalysts by XPS

XPS measurements have shown that tin oxides are more readily reduced to metallic tin by hydrogen in Ni/Al₂O₃ systems than on pure Al₂O₃. During the reductive activation of Sn doped Ni/Al₂O₃ catalysts, surface segregation of the dopant was observed. This finding may explain that tin enhances the selectivity of the steam reforming catalysts only when added in very low concentrations and that it acts as a poison at higher loadings.     

苯酚低温催化水蒸气重整制氢

以Raney Ni为催化剂,在温和条件下(523～723 K)实现了苯酚催化水蒸气重整制氢反应。研究表明,反应温度、液体空速和原料浓度等反应条件是影响苯酚转化率和H₂选择性的重要因素,较高的反应温度和较低的液体空速有利于提高苯酚转化率,但不利于提高H₂选择性。对比苯酚水相重整制氢过程发现,尽管水蒸气重整反应温度相对较高,且需要汽化原料使反应在气相中进行,但该过程具有比水相重整更高的H₂选择性(93%～100%)。此外,Raney Ni催化剂上苯酚水蒸气重整反应与现有的文献结果比较还具有反应条件温和、催化剂稳定性好(60h)以及CO含量低(CO/CO₂摩尔比为0.01～0.2)等优点。将该技术应用于工业含酚有机废水的资源化处理制备的H₂可以直接作为氢源使用。     

Influence of preparation method on performance of Cu(Zn)(Zr)-alumina catalysts for the hydrogen production via steam reforming of methanol

The selective production of hydrogen via steam reforming of methanol (SRM) was performed using prepared catalysts at atmospheric pressure over a temperature range 200–260^∘C. Reverse water gas shift reaction and methanol decomposition reactions also take place simultaneously with the steam reforming reaction producing carbon monoxide which is highly poisonous to the platinum anode of PEM fuel cell, therefore the detailed study of effect of catalyst preparation method and of different promoters on SRM has been carried out for the minimization of carbon monoxide formation and maximization of hydrogen production. Wet impregnation and co-precipitation methods have been comparatively examined for the preparation of precursors to Cu(Zn)(Al₂O₃) and Cu(Zn)(Zr)(Al₂O₃). The catalyst preparation method affected the methanol conversion, hydrogen yield and carbon monoxide formation significantly. Incorporation of zirconia in Cu(Zn)(Al₂O₃) catalyst enhanced the catalytic activity, hydrogen selectivity and also lower the CO formation. Catalyst Cu(Zn)(Zr)(Al₂O₃) with composition Cu/Zn/Zr/Al:12/4/4/80 prepared by co-precipitation method was the most active catalyst giving methanol conversion up to 97% and CO concentration up to 400 ppm. Catalysts were characterized by atomic absorption spectroscopy (AAS), Brunauer-Emett-Teller (BET) surface area, pore volume, pore size and X-ray powder diffraction (XRPD). The XRPD patterns revealed that the addition of zirconia improves the dispersion of copper which resulted in the better catalytic performance of Cu(Zn)(Zr)(Al₂O₃). The time-on-stream (TOS) catalysts stability test was also conducted for which the Cu(Zn)(Zr)(Al₂O₃) catalyst gave the consistent performance for a long time compared to other catalysts.     

A highly efficient Cu/ZnO/Al2O3 catalyst via gel-coprecipitation of oxalate precursors for low-temperature steam reforming of methanol

The impact of preparation methods on the structure and catalytic behavior of Cu/ZnO/Al₂O₃ catalysts for H₂ production from steam reforming of methanol (SRM) has been reported. The results show that the nanostructured Cu/ZnO/Al₂O₃ catalyst obtained by a novel gel-coprecipitation of oxalate precursors has a high specific surface area and high component dispersion, exhibiting much higher activity in the SRM reaction as compared to the catalysts prepared by conventional coprecipitation techniques. It is suggested that the superior catalytic performance of the oxalate gel-coprecipitation-derived Cu/ZnO/Al₂O₃ catalyst could be attributed to the generation of “catalytically active” copper material with a much higher metallic copper specific surface as well as a stronger Cu–Zn interaction due to an easier incorporation of zinc species into CuC₂O₄ · x H₂O precursors as a consequence of isomorphous substitution between copper and zinc in the oxalate gel-precursors.     

Co/La2O3催化乙醇水蒸汽重整制氢反应的研究

采用浸渍、热分解、氢还原等步骤制备了一系列Co/La2O3,催化剂,并将其应用于乙醇水蒸汽重整制氢反应.采用固定床反应考察了温度和水醇比对催化剂性能的影响.用N2吸附、XRD、TPR等手段对催化剂进行了表征.结果表明:5%Co/La2O3,催化剂对乙醇水蒸汽重整制氢反应表现出最高的活性.在500℃、水醇比为3:1时,乙醇的转化率达可到64.8%,H2的产率和选择性分别为1.0 mol/mol和86.1%.另外,在反应温度低于450℃时,H2的选择性可达90%以上.     

Metal oxide catalysts for DME steam reforming: Ga2O3 and Ga2O3–Al2O3 catalysts

The steam reforming of dimethyl ether (DME) was performed on Ga₂O₃–Al₂O₃ mixed oxides prepared by sol–gel method. Ga₂O₃ significantly affects the catalytic performance with respect to the DME conversion and H₂ yield. The catalytic activity increases with the Ga concentration in Ga₂O₃–Al₂O₃ mixed oxides. It is very interesting that without the aid of an additional transition metal component, Ga₂O₃ and Ga₂O₃ containing Al₂O₃ mixed oxide system exhibit good activity in the reforming reaction. To the best of our knowledge, this is the first report that reveals the reforming ability of Ga₂O₃ for the production of H₂ from DME and/or methanol.     

Highly active and stable Rh/MgOAl2O3 catalysts for methane steam reforming

Highly active and coke-resistant Rh catalysts were developed for methane steam reforming in microchannel chemical reactors. Rh loading was optimized on a stable MgOAl₂O₃ support to improve the volumetric productivity for methane conversion. Catalyst activities were stable over a wide range of steam/carbon ratios. In particular, experimental results demonstrated that Rh/MgOAl₂O₃ catalysts are extremely active for methane steam reforming and are resistant to coke formation at stoichiometric steam/carbon ratio of 1 for over 14 h time-on-stream with no sign of deactivation. Methane steam reforming activities on this catalyst is compared in both a microchannel reactor and a conventional micro-tubular reactor. Significant performance enhancement was observed in microchannel reactors owing to improved heat and mass transfer.     

Ni/Al2O3 catalysts and their activity in dehydrogenation of methylcyclohexane for hydrogen production

Previous results on different catalysts revealed that methylcyclohexane underwent selective dehydrogenation to form toluene and hydrogen. This reaction system is a useful prototype model for similar systems in the chemical process and petroleum refining industries, such as hydrotreating for aromatics reduction, desulfurization, denitrogenation, reforming for aromatics reduction, dehydrocyclization, and fuel processing of liquid hydrocarbons in the generation of hydrogen feed for fuel cells. Dehydrogenation of methylcyclohexane to toluene is a method for hydrogen storage in the form of liquid organic hydrides. The efficiency of the dehydrogenation reactions and the quantity of products depend on the catalyst used. In the case of the dehydrogenation of methylcyclohexane to toluene, a metallic function, usually platinum is required as the catalyst. Although, there were some different catalysts used by former researchers, there was almost no investigation about the use of the nickel catalysts for this reaction. From the economical point of view, more efficient catalysts and reaction engineering methods should be developed for these reactions.In this work dehydrogenation of methylcyclohexane was performed in a fixed-bed catalytic reactor in the temperature range of 653–713 K on prepared Ni/Al₂O₃ catalysts having 5, 10, 15 and 20 wt.% Ni content. The inlet flowrates of methylcyclohexane and hydrogen to the reactor were changed by keeping one of them constant in order to investigate their effects on this reaction.     

The positive effect of hydrogen on the reaction of nitric oxide with carbon monoxide over platinum and rhodium catalysts

The effect of adding 330–4930 ppm hydrogen to a reaction mixture of NO and CO (2000 ppm each) over platinum and rhodium catalysts has been investigated at temperatures around 200–250°C. Hydrogen causes large increases in the conversion of NO and, surprisingly, also of CO. Oxygen atoms from the additional NO converted are eventually combined with CO to give CO₂ rather than react with hydrogen to form water. This reaction is described by CO + NO +3/2H₂ CO₂ + NH₃ and accounts for 50–100% of the CO₂ formed with Pt/Al₂O₃ and 20–50% with Rh/Al₂O₃. With the latter catalyst a substantial amount of NO converted produces nitrous oxide. Comparison with a known study of unsupported noble metals suggests that isocyanic acid (HNCO) might be an important intermediate in a reaction system with NO, CO and H₂ present.     

Steam reforming of the aqueous fraction of bio-oil over structured Ru/MgO/Al2O3 catalysts

A catalyst consisting of Ru (5%) dispersed on 15% MgO/Al₂O₃ carrier exhibits high activity and selectivity, as well as satisfactory stability with time on stream, under conditions of steam reforming of acetic acid, a model compound for pyrolysis oil. The presence of MgO in the catalyst formulation is shown to be related to oxygen and/or hydroxyl radical spillover from the carrier to the metal particles. A series of Ru/MgO/Al₂O₃ catalysts supported on cordierite monoliths, ceramic foams and γ-Al₂O₃ pellets were prepared and tested for the production of hydrogen by catalytic steam reforming of the aqueous fraction of bio-oil. All different structural forms of the catalyst exhibited satisfactory activity, converting completely the bio-oil, good selectivity toward hydrogen and satisfactory stability with time on stream. However, the catalyst supported on pellets exhibited the best catalytic performance, among all catalysts investigated. Reforming reactions, and thus hydrogen production, are favoured at high temperatures and low space velocities. Coking is one of the most significant problems encountered in these processes. It was found that only a small part of the incoming carbon is deposited on the catalyst surface, which is mainly present as CH_x. However, coke deposition is more intense on the reactor wall above the catalytic bed, due to homogeneous polymerization of unstable ingredients of bio-oil.