Hydrogen Production from Partial Oxidation and Steam Reforming of N‐octane Over Alumina‐supported Ni and Ni‐Pd Catalysts

Hydrogen production by partial oxidation and steam reforming (POSR) of n‐octane was investigated over alumina‐supported Ni and Ni‐Pd catalysts. It showed that Ni‐Pd/Al₂O₃ had higher activity and hydrogen selectivity than the nickel catalyst under the experimental conditions, which indicated Ni‐Pd/Al₂O₃ could be an effective catalyst for the production of hydrogen from hydrocarbons.     

Hydrogen Production from Glycerol Over Nickel Catalysts Supported on Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Modified by Mg,Zr, Ce or La

Hydrogen production from glycerol reforming in liquid (aqueous phase reforming, APR) and vapor (steam reforming SR) phase over alumina-supported nickel catalysts modified with Ce, Mg, Zr and La was studied. Characterization of catalysts by temperature programmed reduction and XPS analyses revealed important structural effects: (i) the intercalation of Mg between nickel and alumina that inhibited the alumina incorporation to nickel phases, (ii) the close contact between Ni and Zr phases and, (iii) the close surface interaction of La and Ce ions with NiO phases. The catalytic activity of the samples studied in this work clearly indicated the different catalyst functionalities necessary to carry out aqueous-phase and vapor-phase steam reforming of glycerol. For aqueous phase reforming of glycerol, the addition of Ce, La and Zr to Ni/Al₂O₃ improves the initial glycerol conversions obtained over the Ni/Al₂O₃ supported catalyst. It is suggested that the differences in catalytic activities are related with geometric effects caused by the decoration of Ni phases by Ce and La or by the close interaction between Ni and Zr. In spite that nickel catalysts showed high APR activities at initial times on stream, all samples showed, independently of support, important deactivation rates that deactivate the catalysts after few hours under operation. Catalysts characterization after APR showed the oxidation of the active metallic Ni during reaction as the main cause of the observed deactivation. In the case of the glycerol steam reforming in vapor phase, the use of Ce, La, Mg and Zr as promoters of Ni based catalysts increases the hydrogen selectivity. Differences in activity were explained in terms of enhancement in: surface nickel concentration (Mg), capacity to activate steam (Zr) and stability of nickel phases under reaction conditions (Ce and La).     

Hydrogen Production by Steam Reforming of Liquefied Natural Gas Over Mesoporous Ni-Al2O3 Composite Catalyst Prepared by a Single-step Non-ionic Surfactant-templating Method

A mesoporous Ni-Al₂O₃ composite catalyst (Ni-A-NS) was prepared by a single-step non-ionic surfactant-templating method for use in hydrogen production by steam reforming of liquefied natural gas (LNG). For comparison, a nickel catalyst supported on mesoporous alumina (Ni/A-NS) was also prepared by an impregnation method. The effect of physicochemical properties on the performance of Ni-A-NS catalyst in the steam reforming of LNG was investigated. Ni-A-NS catalyst retained superior textural properties compared to Ni/A-NS catalyst. Nickel oxide species were highly dispersed on the surface of both Ni/A-NS and Ni-A-NS catalysts through the formation of surface nickel aluminate phase. Although both Ni/A-NS and Ni-A-NS catalysts exhibited a stable catalytic performance, Ni-A-NS catalyst showed a better catalytic performance than Ni/A-NS catalyst in the steam reforming of LNG. High nickel surface area and high nickel dispersion of Ni-A-NS catalyst played an important role in enhancing the dehydrogenation reaction of hydrocarbon species and the gasification reaction of adsorbed carbon species in the steam reforming of LNG. High reducibility of Ni-A-NS catalyst was also responsible for its high catalytic performance.     

Hydrogen production on Ni–Pd–Ce/γ-Al2O3 catalyst by partial oxidation and steam reforming of hydrocarbons for potential application in fuel cells

A series of catalysts of nickel–palladium–cerium supported upon alumina have been investigated in order to obtain a suitable catalyst that could be used in the process of producing hydrogen for the potential application in fuel cell by partial oxidation and steam reforming (POSR) of mixtures of hydrocarbons. Investigated results showed that little addition of cerium into Ni–Pd catalyst could definitely improve its stability of hydrogen production from mixtures of hydrocarbons by POSR method. The experimental results also showed that the optimum compositions of Ni–Pd–Ce catalyst were the molar ratio of Ni to Pd as 1:0.09 and containing of Ce 0.5 wt%, shortened as Ni–Pd–Ce-0.5 catalyst. XRD results for the typical catalysts showed that it mainly displayed the γ-Al₂O₃ and Ni peaks. SEM and TG results for the fresh and used Ni–Pd–Ce-0.5 catalysts, lasted for 540 h, did not show much difference on their surface patterns and TG curves, respectively. This indicated this catalyst would be a practical catalyst to produce hydrogen from liquid fuel by POSR method for potential application in fuel cells.     

Ni Catalysts Supported on Mesoporous Nanocrystalline Magnesium Silicate in Dry and Steam Reforming Reactions

Mesoporous nanocrystalline MgSiO₃ with high surface area was synthesized by a hydrothermal method and employed as support in dry and steam reforming of methane. Ni/MgSiO₃ catalysts were prepared by an impregnation method and characterized by different techniques. N₂ adsorption analysis indicated that addition of nickel shifted the pore size distributions to smaller sizes. Temperature‐programmed reduction analysis revealed that a higher nickel loading enhanced the reducibility of the catalyst. The catalytic performance was improved with increasing the nickel content. The Ni/MgSiO₃ catalyst exhibited high stability in dry reforming but methane conversion declined with time‐on‐stream in the steam reforming reaction. Temperature‐programmed oxidation profiles of spent catalysts indicated that the high amount of carbon deposited on the catalyst surface in dry and steam reforming was assigned to whisker‐type carbon.     

Production of Middle Distillate Through Hydrocracking of Paraffin Wax Over NiMo/SiO2-Al2O3 Catalysts: Effect of Solvent in the Preparation of SiO2-Al2O3 by a Sol–Gel Method

Mesoporous Ni-Al₂O₃ (XNiAl) catalysts with different Ni/Al atomic ratio (X) were prepared by a co-precipitation method for use in hydrogen production by steam reforming of liquefied natural gas (LNG). The effect of Ni/Al atomic ratio of mesoporous XNiAl catalysts on their physicochemical properties and catalytic activity for steam reforming of LNG was investigated. Physical properties of XNiAl catalysts did not show a consistent trend with respect to Ni/Al atomic ratio, while chemical properties of XNiAl catalysts strongly influenced by Ni/Al atomic ratio. Nickel species were highly dispersed on the surface of XNiAl catalysts through the formation of nickel aluminate phase or solid solution of nickel oxide and nickel aluminate phase. In the steam reforming of LNG, both LNG conversion and hydrogen composition in dry gas showed volcano-shaped curves with respect to Ni/Al atomic ratio. Nickel surface area of XNiAl catalysts was well correlated with LNG conversion and hydrogen composition over the catalysts. Among the catalysts tested, 0.8NiAl (Ni/Al = 0.8) catalyst with the highest nickel surface area showed the best catalytic performance.     

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%.     

Preparation of Highly Active Nickel Catalysts Supported on Mesoporous Nanocrystalline γ‐Al2O3 for Methane Autothermal Reforming

Autothermal reforming (ATR) of methane was carried out over nanocrystalline Al₂O₃‐supported Ni catalysts with various Ni loadings. Mesoporous nanocrystalline γ‐Al₂O₃ powder with high specific surface area was prepared by the sol‐gel method and employed as support for the nickel catalysts. The prepared samples were characterized by X‐ray diffraction, Brunauer‐Emmett‐Teller, temperature‐programmed reduction, temperature‐programmed hydrogenation, and scanning electron microscopy techniques. It is demonstrated that the methane conversion increased with increasing in Ni content and that the catalyst with 25 wt % Ni exhibited the highest activity and a stable catalytic performance in the ATR process, with a low degree of carbon formation. Furthermore, the effects of the reaction temperature, the calcination temperature, the steam/CH₄ and O₂/CH₄ ratios, and the gas hourly space velocity on the catalytic performance of the 25 % Ni/Al₂O₃ catalyst were investigated.     

Effect of calcination temperature of mesoporous nickel–alumina catalysts on their catalytic performance in hydrogen production by steam reforming of liquefied natural gas (LNG)

Mesoporous nickel–alumina (Ni–A-NS) catalysts prepared by a non-ionic surfactant-templating method were calcined at various temperatures for use in hydrogen production by steam reforming of liquefied natural gas (LNG). The effect of calcination temperature of nickel–alumina catalysts on their physicochemical properties and catalytic activity for steam reforming of LNG was investigated. Nickel oxide species were finely dispersed on the surface of Ni–A-NS catalysts through the formation of nickel aluminate phase. Reducibility, nickel surface area, and nickel dispersion of Ni–A-NS catalysts decreased with increasing calcination temperature. In the steam reforming of LNG, both LNG conversion and hydrogen composition in dry gas decreased with increasing calcination temperature of Ni–A-NS catalysts. Nickel surface area and reducibility of Ni–A-NS catalysts were well correlated with catalytic performance of the catalysts. Among the catalysts tested, Ni–A-NS700 (nickel–alumina catalyst calcined at 700 °C) with the highest nickel surface area and the highest reducibility exhibited the best catalytic performance.     

Investigation of the catalytic performance of Ni/MgO catalysts in partial oxidation,dry reforming and combined reforming of methane

Dry reforming, partial oxidation and combined reforming of methane (combination of partial oxidation and dry reforming) to synthesis gas over nickel catalysts supported on nanocrystalline magnesium oxide with various nickel loadings have been studied. Among the catalysts evaluated, catalyst with 15 wt.% nickel content revealed the most active catalytic performance toward dry reforming, partial oxidation and combined reforming reactions. In addition, catalyst with 5 wt.% nickel loading was employed in long term stability test and has shown stable catalytic performance up to 50 h time on stream without any decrease in methane conversion in these three processes.     

Addition effect of ruthenium on nickel steam reforming catalysts

Several Ni-based catalysts supported on a mixture of MgO, La₂O₃, and Al₂O₃ were prepared. The catalytic performance in the steam reforming of m-cresol was evaluated. In the investigation of the effect of Ru loading added to the Ni-catalyst, it was found that the presence of Ru strongly enhances the catalytic performance of the Ni-based catalyst when increasing Ru loading up to 2 wt%. Effect of Ni loading to the Ru-based catalyst system was also investigated. It was found that the addition of nickel to the Ru-based catalyst up to 15 wt% enhanced significantly the catalytic activity of the catalyst. The lifetime of the Ru–Ni catalysts in the reforming of m-cresol was further tested at 750 °C. In agreement with general observations of the use of Ni monometallic catalyst, deactivation of the catalyst due to the carbon deposition reaction already occurred in the reforming of the oxygenated compound. On the other hand, a reasonable high resistant on the carbon deposition in the reforming of m-cresol was given by the 2 wt% Ru–15 wt% Ni catalyst system. An effort in improving the strength of the catalyst support with this catalyst system was also conducted, and the catalyst showed significant increase in the stability of the reforming of oxygenated aromatic compound.     

The effects of La2O3 on the structural properties of La2O3–Al2O3 prepared by the sol–gel method and on the catalytic performance of Pt/La2O3–Al2O3 towards steam reforming and partial oxidation of methane

The effect of La₂O₃ content on the structural properties and catalytic behavior of Pt/xLa₂O₃–Al₂O₃ catalysts in steam reforming of methane and partial oxidation of methane was investigated. There was a decrease in the density of Pt sites with the increase of La₂O₃ loadings according to Fourier transform infrared spectroscopy of adsorbed CO and to dehydrogenation of cyclohexane results. However, transmission electron microscopy data indicates an opposite trend. This apparent disagreement could be due to the partial coverage of Pt sites by LaO_x species. CH₄ turnover rates and specific rates of steam reforming of methane increased for higher La₂O₃ loadings. The Pt/Al₂O₃ catalyst was strongly deactivated during partial oxidation of methane, while La₂O₃-containing catalysts exhibited higher stability. The increase of activity observed during the reactions was ascribed to the ability of the [LaPt_xO]Pt⁰-like species to promote the gasification of coke. This cleaning mechanism led to higher accessibility of the active sites to CH₄.     

Autothermal reforming of methane over Ni/γ-Al2O3 promoted with Pd: The effect of the Pd source in activity,temperature profile of reactor and in ignition

The effects of adding small amounts of palladium to Ni/γ-Al₂O₃ catalysts for the autothermal reforming of methane, in terms of activity, reducibility, capacity of repeated ignition and temperature profile of the reactor are described. The effect of different Pd sources was also studied. The Pd addition favors nickel reduction at lower temperatures. When the palladium is added as PdCl₂ (PdNiAl-Cl) it exhibits a higher reduction temperature than when Pd(NO₃)₂ (PdNiAl-N) is used, an this can be attributed to the formation of Pd_xCl_yO_z species. Palladium strongly increases the activity of the Ni catalyst in autothermal reforming of methane, which is proportional to an increase in metal surface area. The addition of palladium to the catalyst also leads to a flatter temperature profile through the catalytic bed in the autothermal reforming of methane, and this is assigned to the high surface metal area of the catalyst. Only PdNiAl-N catalyst catalyzes the autothermal reforming of methane without previous reduction, while the PdNiAl-Cl catalyst only catalyzes the methane combustion and the unpromoted catalyst was inactive.     

The effects of La2O3 on the structural properties of La2O3–Al2O3 prepared by the sol–gel method and on the catalytic performance of Pt/La2O3–Al2O3 towards steam reforming and partial oxidation of methane

The effect of La₂O₃ content on the structural properties and catalytic behavior of Pt/xLa₂O₃–Al₂O₃ catalysts in steam reforming of methane and partial oxidation of methane was investigated. There was a decrease in the density of Pt sites with the increase of La₂O₃ loadings according to Fourier transform infrared spectroscopy of adsorbed CO and to dehydrogenation of cyclohexane results. However, transmission electron microscopy data indicates an opposite trend. This apparent disagreement could be due to the partial coverage of Pt sites by LaO_x species. CH₄ turnover rates and specific rates of steam reforming of methane increased for higher La₂O₃ loadings. The Pt/Al₂O₃ catalyst was strongly deactivated during partial oxidation of methane, while La₂O₃-containing catalysts exhibited higher stability. The increase of activity observed during the reactions was ascribed to the ability of the [LaPt_xO]Pt⁰-like species to promote the gasification of coke. This cleaning mechanism led to higher accessibility of the active sites to CH₄.     

Characterization of aerogel Ni/Al2O3 catalysts and investigation on their stability for CH4-CO2 reforming in a fluidized bed

The CH₄-CO₂ reforming was investigated in a fluidized bed reactor using nano-sized aerogel Ni/Al₂O₃ catalysts, which were prepared via a sol–gel method combined with a supercritical drying process. The catalysts were characterized with BET, XRD, H₂-TPR and H₂-TPD techniques. Compared with the impregnation catalyst, aerogel catalysts exhibited higher specific surface areas, lower bulk density, smaller Ni particle sizes, stronger metal-support interaction and higher Ni dispersion degrees. All tested aerogel catalysts showed better catalytic activities and stability than the impregnation catalyst. Their catalytic stability tested during 48 h reforming was dependent on their Ni loadings. Characterizations of spent catalysts indicated that only limited graphitic carbon formed on the aerogel catalyst, while massive graphitic carbon with filamentous morphology was observed for the impregnation catalyst, leading to significant catalytic activity degradation. An aerogel catalyst containing 10% Ni showed the best catalytic stability and the lowest rate of carbon deposition among the aerogel catalysts due to its small Ni particle size and strong metal-support interaction.     

Effect of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-ZrO<Subscript>2</Subscript> xerogel support on hydrogen production by steam reforming of LNG over Ni/Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-ZrO<Subscript>2</Subscript> catalyst

An Al₂O₃-ZrO₂ xerogel (AZ-SG) was prepared by a sol-gel method for use as a support for a nickel catalyst. The Ni/AZ-SG catalyst was then prepared by an impregnation method, and was applied to hydrogen production by steam reforming of LNG. A nickel catalyst supported on commercial alumina (A-C) was also prepared (Ni/A-C) for comparison. The hydroxyl-rich surface of the AZ-SG support increased the dispersion of nickel species on the support during the calcination step. The formation of a surface nickel aluminate-like phase in the Ni/AZ-SG catalyst greatly enhanced the reducibility of the Ni/AZ-SG catalyst. The ZrO₂ in the AZ-SG support increased the adsorption of steam onto the support and the subsequent spillover of steam from the support to the active nickel sites in the Ni/AZ-SG catalyst. Both the high surface area and the well-developed mesoporosity of the Ni/AZ-SG catalyst improved the gasification of adsorbed surface hydrocarbons in the reaction. In the steam reforming of LNG, the Ni/AZ-SG catalyst showed a better catalytic performance than the Ni/A-C catalyst. Moreover, the Ni/AZ-SG catalyst showed strong resistance toward catalyst deactivation.     

Effect of support on the conversion of methane to synthesis gas over supported iridium catalysts

A partial oxidation of methane was carried out using iridium catalysts supported on several metal oxides. The productivity of the synthesis gas from methane was strongly affected by the choice of support oxides for the catalysts. The synthesis gas production proceeded basically via a two-step reaction consisting of methane combustion to give H₂O and CO₂, followed by the reforming of methane from CO₂ and steam. Although the combustion and the reforming of methane from steam did not depend upon the catalyst support, a large variation in the catalytic activity for the reforming of methane from CO₂ was observed over Ir catalysts with different supports. The support activity order in the reforming of methane from CO₂ with iridium catalysts was as follows: TiO₂≧ZrO₂≧Y₂O₃>La₂O₃>MgO≧Al₂O₃>SiO₂. The same order was observed in the synthesis gas production from the partial oxidation of methane. This revised version was published online in August 2006 with corrections to the Cover Date.     

Steam Reforming of Sunflower Oil over Ni/Al Catalysts Prepared from Hydrotalcite-Like Materials

Using catalytic steam reforming of biofuels to produce hydrogen for energy systems based on fuel cells is an option that may help to reduce the net emissions of CO₂ into the atmosphere. Vegetable oils are some of the most interesting options because of their high potential yield of hydrogen. They are, however, more difficult to reform than the light hydrocarbon feedstocks that are used for producing hydrogen industrially by steam reforming. Catalysts prepared from hydrotalcite-like materials are promising for use in the steam reforming of vegetable oils, since their catalytic activity is significantly higher than that of commercial catalysts for hydrocarbon steam reforming. In this paper, a study is made of how the nickel content of HT-derived catalysts affects their activity for steam reforming of sunflower oil. Three catalysts were prepared with Ni/Al atomic ratios of 1, 2, and 3, respectively. The samples were characterized by various techniques to correlate their activity with the structural characteristics of the catalysts: X-ray diffraction (XRD), BET, thermogravimetric analysis (TGA), and hydrogen chemisorption. The results showed that the catalyst activity increased as the nickel content in the material decreased. The support and its properties seemed to play a key role in the performance of the HT-derived catalysts. This is probably because a decrease in the Ni content produces a better dispersion of the metal and higher BET areas, which leads to a higher capacity for water adsorption. With the most active catalyst (Ni/Al of 1), 2.2 mol H₂/(g_cat h) was produced at 575 °C, 2 bar, and a steam-to-carbon ratio of 3.     

Mixed and autothermal reforming of methane with supported Ni catalysts with a core/shell structure

Supported nickel catalysts with a core/shell structure of Ni/Al₂O₃ and Ni/MgO-Al₂O₃ synthesized under multi-bubble sonoluminescence (MBSL) conditions were tested for mixed steam and dry (CO₂) reforming and autothermal reforming of methane. In the previous tests, the supported Ni catalysts made of 10% Ni loading on Al₂O₃ or MgO-Al₂O₃ had shown good performances in the steam reforming of methane (methane conversion of 97% at 750 °C), in the partial oxidation of methane (methane conversion of 96% at 800 °C) and in dry reforming of methane (methane conversion of 96% at 850 °C) and showed high thermal stability for the first 50-150 h. In this study, the supported Ni catalysts showed good performance in the mixed and autothermal reforming of methane with their excellent thermal stability for the first 50 h. In addition, very interestingly, there was no appreciable carbon deposition on the surface of the tested catalysts after the reforming reaction.     

Ethanol reforming and partial oxidation with Cu/Nb2O5 catalyst

Ethanol reforming and partial oxidation were studied on Cu/Nb₂O₅ and Ni/Al₂O₃ catalysts. Compared to the Ni/Al₂O₃ catalyst, the Cu/Nb₂O₅ catalyst presents conversion as high as Ni/Al₂O₃ catalyst, however, for the same level of formation of hydrogen it occurs at much lower temperature on the Cu/Nb₂O₅ catalyst, 200 °C lower than for the Ni/Al₂O₃ catalyst, with remarkable little formation of CO, which can be attributed to the strong interaction between copper and niobia. Temperature-programmed desorption (TPD-ethanol) and surface reactions (TPSR) of partial oxidation of ethanol showed formation of ethylene, acetaldehyde, ethane and mainly H₂ and CO₂ besides little methane. DRIFTS results are in accordance with TPD analysis and the formation of acetate species at room temperature suggests reactivity of the surface and its oxidative dehydrogenation capacity. The adsorption of ethanol gives rise to ethoxide species, which form acetate and acetaldehyde that can be oxidized to CO₂ via carbonate. A comparison with reported results for Cu/Al₂O₃ this catalyst is promising, yielding high level of H₂ with little CO production during reforming and partial oxidation reaction. The maximum H₂ formation for the partial oxidation of ethanol was 41% at ratio (O₂/Et) 0.8, increasing to 50% at ratio 1.5. The H₂/CO is around 10 for the partial oxidation and 7 for steam reforming, which is excellent, compared to the Ni/Al₂O₃ catalyst with a factor 4–8 lower.