Steam reforming of ethanol over skeletal Ni‐based catalysts: A temperature programmed desorption and kinetic study

An investigation on reaction scheme and kinetics for ethanol steam reforming on skeletal nickel catalysts is described. Catalytic activity of skeletal nickel catalyst for low‐temperature steam reforming has been studied in detail, and the reasons for its high reactivity for H₂ production are attained by probe reactions. Higher activity of water gas shift reaction and methanation contributes to the low CO selectivity. Cu and Pt addition can promote WGSR and suppress methanation, and, thus, improve H₂ production. A reaction scheme on skeletal nickel catalyst has been proposed through temperature programmed reaction spectroscopy experiments. An Eley‐Rideal model is put forward for kinetic studies, which contains three surface reactions: ethanol decomposition, water gas shift reaction, and methane steam reforming reaction. The kinetics was studied at 300–400°C using a randomized algorithms method and a least‐squares method to solve the differential equations and fit the experimental data; the goodness of fit obtained with this model is above 0.95. The activation energies for the ethanol decomposition, methane steam reforming, and water gas shift reaction are 187.7 kJ/mol, 138.5 kJ/mol and 52.8 kJ/mol, respectively. Thus, ethanol decomposition was determined to be the rate determining reaction of ethanol steam reforming on skeletal nickel catalysts. © 2013 American Institute of Chemical Engineers AIChE J 60: 635–644, 2014     

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.     

Catalytic activity evaluation for hydrogen production via autothermal reforming of methane

A nickel catalyst (5.75 wt.%) supported on gamma-alumina was evaluated through autothermal reforming of methane (ATR). The reforming process was pointed to hydrogen production, following thermodynamic and stoichiometric predictions. The catalyst was characterised by several methods including atomic absorption spectroscopy (AAS), B.E.T.-N₂, X-ray diffraction (XRD), scanning electron microscope (SEM) and thermal analyses (thermogravimetry, TG; derivate thermogravimetry, DTG; and differential thermal analysis, DTA). Experimental evaluations in a fixed-bed reactor (1023–1123 K, 1.00 bar, 150–400 cm³/min feed) presented methane conversions in the range of 40–65%. The effluent mixtures provided hydrogen yields in the range of 78–84%, carbon monoxide 3–14%, and carbon dioxide 5–18%. High molar H₂/CO ratios, ranging from 8 to 90, were obtained. Operating autothermal conditions (excess of steam, 1023–1123 K, 1.00 bar) provided low coke formation and high hydrogen selectivity (81%) for methane reforming.     

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.     

Stable equilibrium shift of methane steam reforming in membrane reactors with hydrogen‐selective silica membranes

Equilibrium shifts of methane steam reforming in membrane reactors consisting of either tetramethoxysilane‐derived amorphous hydrogen‐selective silica membrane and rhodium catalysts, or hexamethyldisiloxane‐derived membrane and nickel catalysts is experimentally demonstrated. The hexamethyldisiloxane‐derived silica membrane showed stable permeance as high as 8 × 10^?8 mol m^?2 s^?1 Pa^?1 of H₂ after exposure to 76 kPa of vapor pressure at 773 K for 60 h, which was a much better performance than that from the tetramethoxysilane‐derived silica membrane. Furthermore, the better silica membrane also maintained selectivity of H₂/N₂ as high as 10³ under the above hydrothermal conditions. The degree of the equilibrium shifts under various feedrate and pressure conditions coincided with the order of H₂ permeance. In addition, the equilibrium shift of methane steam reforming was stable for 30 h with an S/C ratio of 2.5 at 773 K using a membrane reactor integrated with hexamethyldisiloxane‐derived membrane and nickel catalyst. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Steam reforming of bio-oil derived small organics over the Ni/Al2O3 catalyst prepared by an impregnation–reduction method

An impregnation–reduction method has been developed in this study to prepare the Ni/Al₂O₃ catalyst for steam reforming of bio-oil model compounds for hydrogen production. This method can alleviate the interactions between nickel species and an alumina carrier and promote metal dispersion and utilization of the nickel species, achieving a highly active, selective and stable reforming catalyst. Moreover, this method is very simple and fast. Only the impregnation and reduction steps are involved and the catalyst can be prepared in situ. In addition, coke formation in steam reforming is not uniform on a catalyst bed. Coking in the topmost catalyst layer is much more serious.     

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.     

Simultaneous oxidative conversion and CO2 or steam reforming of methane to syngas over CoO–NiO–MgO catalyst

CO₂ reforming, oxidative conversion and simultaneous oxidative conversion and CO₂ or steam reforming of methane to syngas (CO and H₂) over NiO–CoO–MgO (Co: Ni: Mg=0·5: 0·5:1·0) solid solution at 700–850°C and high space velocity (5·1×10⁵ cm³ g⁻¹ h⁻¹ for oxidative conversion and 4·5×10⁴ cm³ g⁻¹ h⁻¹ for oxy-steam or oxy-CO₂ reforming) for different CH₄/O₂ (1·8–8·0) and CH₄/CO₂ or H₂O (1·5–8·4) ratios have been thoroughly investigated. Because of the replacement of 50 mol% of the NiO by CoO in NiO–MgO (Ni/Mg=1·0), the performance of the catalyst in the methane to syngas conversion process is improved; the carbon formation on the catalyst is drastically reduced. The CoO–NiO–MgO catalyst shows high methane conversion activity (methane conversion >80%) and high selectivity for both CO and H₂ in the oxy-CO₂ reforming and oxy-steam reforming processes at ⩾800°C. The oxy-steam or CO₂ reforming process involves the coupling of the exothermic oxidative conversion and endothermic CO₂ or steam reforming reactions, making these processes highly energy efficient and also safe to operate. These processes can be made thermoneutral or mildly exothermic or mildly endothermic by manipulating the process conditions (viz. temperature and/or CH₄/O₂ ratio in the feed). © 1998 Society of Chemistry Industry     

A Kinetic Study of Ethanol Steam Reforming Using a Nickel Based Catalyst

A kinetic study of ethanol steam reforming to produce hydrogen within the region of kinetic rate control was carried out. A Ni(II)–Al(III) lamellar double hydroxide as catalyst precursor was used. H₂, CO, CO₂ and CH₄ were obtained as products. Using the Langmuir–Hinshelwood (L–H) approach, two kinetic models were proposed. The first was a general model including four reactions, two of them corresponding to ethanol steam reforming and the other two to methane steam reforming. When high temperatures and/or high water/ethanol feed ratios were used, the system could be reduced to two irreversible ethanol steam reforming reactions.     

Testing of a Ni‐Al2O3 Catalyst for Methane Steam Reforming Using Different Reaction Systems

Ni‐Al₂O₃ catalyst activity was tested for methane steam reforming using two different reaction systems: a catalyst particle bed (0.42–0.5 mm catalyst particles diluted in SiC) with a surface area‐to‐volume ratio SA/V of 910 m^–1 and a porosity ? of 52 % and a catalyst‐coated metal monolith with an SA/V of 3300 m^–1 and an ? of 86 %. Under a steam‐to‐carbon ratio of 2.5 and at a temperature of 700 °C, the highest specific reaction rates were found for the catalyst‐coated monolith. The high SA/V and ?, together with the high rate of heat transfer of the metal monolith were found to be responsible of this optimum behavior. However, in both systems, the Ni‐Al₂O₃ catalyst suffered a catalyst deactivation during operation.     

Investigation of alumina-supported Ni and Ni-Pd catalysts by partial oxidation and steam reforming of n-octane

Aseries of nickel and nickel-palladium supported upon alumina catalysts were prepared in order to obtain a suitable catalyst that could be used in the process of producing hydrogen by partial oxidation and steam reforming of n-octane. Hydrogen production by partial oxidation and steam reforming (POSR) of n-octane was investigated over alumina-supported Ni and Ni-Pd catalysts. The process occurred by a combination of exothermic partial oxidation and endothermic steam reforming of n-octane. It was found that Ni/Al₂O₃ catalyst activity was high at high temperatures and increased with the Ni loadings. Its activity, however, was not obviously increased when Ni loadings were over 5.0 wt%. Compared with nickel catalyst, the bimetallic catalyst of Ni-Pd/A1₂O₃ showed markedly increased activity and hydrogen selectivity at experimental conditions. The catalytic performance also became more stable when the palladium was added, which indicated that palladium plays an essential role in the catalytic action. The used catalysts of Ni-Pd/A1₂O₃ were regenerated three times by using air at space velocity of 2,000 h⁻¹ to obtain a long duration catalyst. Also, the typical catalyst was characterized by using SEM, BET, TG and ICP methods in detail.     

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.     

Interactions of supported nickel and nickel oxide catalysts with methane and steam at high temperatures

The catalytic performance of cermets made of 10% nickel or nickel oxide supported on YSZ (yttria-stabilized zirconia) for chemical looping combustion (CLC) and steam reforming (SR) of methane at 700 °C is investigated. Steam reforming of methane over the reduced catalyst resulted in a syngas containing more than 70% hydrogen and about 15% carbon monoxide. Chemical looping combustion of methane with insufficient lattice oxygen could potentially lead to 40–65% hydrogen rich gas products. Prolonged induction period (e.g. 30–80 min) in reduction of nickel oxide by methane has been observed in the presence of steam. The span of induction period increases by increasing steam partial pressure. It is hypothesized that the delayed reduction of nickel oxide is related to the retarding effect of steam on autocatalytic reactions of methane and hydrogen with lattice oxygen of nickel oxide and the subsequent reforming reactions.     

The effect of the addition of Y2O3 to Ni/α-Al2O3 catalysts on the autothermal reforming of methane

The addition of Y₂O₃ to Ni/α-Al₂O₃ catalysts was investigated by BET surface area measurements, hydrogen chemisorption, X-ray diffraction, UV–vis diffuse reflectance spectroscopy, X-ray fluorescence, temperature programmed reduction, temperature programmed oxidation and cyclohexane dehydrogenation. Autothermal reforming experiments were performed in order to evaluate the methane conversion and proceeded through an indirect mechanism consisting of total combustion of methane followed by CO₂ and steam reforming generating the synthesis gas. The Y₂O₃·Al₂O₃ supported catalysts presented better activity and stability in autothermal reforming reaction. Temperature programmed oxidation analysis demonstrated that the addition of Y₂O₃ resulted in a change of the type or the location of coke formed during reaction. None of the prepared catalyst presented deactivation by sintering under the tested conditions. The improved stability of supported catalysts Y₂O₃·Al₂O₃ was the result of minimizing the formation of coke on the surface of nickel particles.     

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).     

CH4 reforming with CO2 for syngas production over nickel catalysts supported on mesoporous nanostructured γ-Al2O3

Nanostructured γ-Al₂O₃ with high surface area and mesoporous structure was synthesized by sol-gel method and employed as catalyst support for nickel catalysts in methane reforming with carbon dioxide. The prepared samples were characterized by XRD, BET, TPR, TPH, SEM and TPO techniques. The BET analysis showed a high surface area of 204m²g^?1 and a narrow pore-size distribution centered at a diameter of 5.5 nm for catalyst support. The results revealed that an increase in nickel loading from 5 to 15 wt% decreased the surface area of catalyst from 182 to 160 m²g^?1. In addition, the catalytic results showed an increase in methane conversion with increase in nickel content. TPO analysis revealed that the coke deposition increased with increasing in nickel loading, and the catalyst with 15 wt% of nickel showed the highest degree of carbon formation. SEM and TPH analyses confirmed the formation of whisker type carbon over the spent catalysts. Increasing CO₂/CH₄ ratio increased the methane conversion. The BET analysis of spent catalysts indicated that the mesoporous structure of catalysts still remained after reaction.     

A dual catalyst bed for the autothermal partial oxidation of methane to synthesis gas

Dual bed catalysts were found to produce high yields (>85%) of hydrogen from methane and air in a millisecond contact time reactor. The dual bed catalyst consisted of a 5 mm platinum combustion catalyst followed by a 5 mm nickel steam reforming catalyst. The platinum catalyst was used to totally oxidize approximately one-quarter of the methane feed to carbon dioxide and water. In the nickel catalyst, the carbon dioxide and water reformed the remaining methane to hydrogen and carbon monoxide. This process is favored at high flow rates, because the heat generated in the platinum catalyst is convected to the nickel catalyst at a higher rate. The heat delivered to the nickel catalyst favors the endothermic reforming reactions that generate the hydrogen and carbon monoxide.     

Hydrogen production by sorption-enhanced steam methane reforming process using CaO-Zr/Ni bifunctional sorbent–catalyst

A bifunctional CaO-Zr/Ni (13, 18, and 20.5 wt% NiO) sorbent–catalyst was developed using the wet-mixing/sonication technique and applied for hydrogen production by sorption-enhanced steam methane reforming (SESMR), an intensified process that integrates hydrogen production with CO₂ capture. The material was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and N₂ physisorption (BET). CO₂ sorption efficiency of the developed materials was evaluated during 25 CO₂ sorption/regeneration cycles. The prepared sorbent–catalysts were then applied in the SESMR during 10 reaction cycles. The results showed that the bifunctional sorbent–catalyst with 20.5 wt% NiO loading presented the most suitable activity. The H₂ yield of ∼91% at the end of the 10th SESMR cycle is considerably higher than equilibrium H₂ yield that could be obtained by traditional steam methane reforming.     

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.     

Analysis of hydrogen production from methane autothermal reformer with a dual catalyst-bed configuration

This paper presents a performance analysis of a dual-bed autothermal reformer for hydrogen production from methane using a non-isothermal, one dimensional reactor model. The first section of Pt/Al₂O₃ catalyst is designed for oxidation reaction, whereas the second one based on Ni/MgAl₂O₄ catalyst involves steam reforming reaction. The simulation results show that the dual-bed autothermal reactor provides higher reactor temperature and methane conversion compared with a conventional fixed-bed reformer. The H₂O/CH₄ and O₂/CH₄ feed ratios affect the methane conversion and the H₂/CO product ratio. The addition of steam at lower temperatures to the steam reforming section of the dual-bed reactor can produce the synthesis gas with a higher H₂/CO product ratio.