Oxidative Steam Reforming Research Articles

Stable hydrogen production by methane steam reforming in a two-zone fluidized-bed reactor: Effect of the operating variables

The oxidative steam reforming of methane in a two-zone fluidized-bed reactor (TZFBR) was investigated over a Ni/Al2O3 catalyst. The effects of the main operating variables (temperature, steam/oxygen ratio, steam/methane ratio and relative velocity with respect to the minimum fluidization velocity) have been studied. A comparison has been made with results given in the literature in terms of hydrogen yield. Despite working with very low steam/methane ratios, high values of hydrogen yield at both high methane conversion and at steady state were obtained in the TZFBR.

Review of methanol reforming-Cu-based catalysts, surface reaction mechanisms, and reaction schemes

Recent development in proton-exchange membrane fuel cell technology has stimulated research in fuel processing for hydrogen production. Hydrogen can be produced from four different types of methanol reforming processes, namely methanol decomposition, partial oxidation of methanol, steam reforming of methanol and oxidative steam reforming of methanol. This review paper discusses commonly used Cu-based catalysts including their kinetic, compositional, and morphological characteristics in methanol reforming reactions. Although research exploring surface reaction mechanism over various Cu-based catalysts was first attempted about three decades ago, the scheme remains controversial. This technical discussion will focus on the commonly reported surface intermediate species, which are methoxy, formaldehyde, dioxymethylene, formate and methyl formate. The surface reaction mechanism could be complicated by the introduction of reactants such as oxygen and steam, into the system as they would subsequently initiate secondary reactions. Different reaction schemes of methanol reforming are presented.

Oxidative steam reforming of ethanol over Rh catalyst supported on Ce1−xLaxOy (x = 0.3) solid solution prepared by urea co-precipitation method

A Ce1−xLaxOy solid solution (CL) is prepared by a co-precipitation method using urea as a precipitant, with varying urea/metal molar ratio (N). The supported rhodium catalysts are then prepared by an impregnation method for use in hydrogen production from oxidative steam reforming (OSR) of ethanol. X-ray diffraction and Raman spectra results confirm the formation of CL, and the crystal structures of these catalysts are not very sensitive to the urea/metal molar ratios (N = 5–15). However, the surface area and reducibility of the Rh/CL-N catalysts decrease monotonically with increasing N. During the OSR process, a similar tendency is also observed for ethanol conversion and hydrogen selectivity. Among the catalysts tested, Rh/CL-5 shows the best catalytic performance, achieving >97% ethanol conversion at 300 °C with H2 yield rate of 210 μmol g-cat−1 s−1. At 450 °C, its hydrogen selectivity reaches 117%, with no observable change after 72 h aging.

Oxidative steam reforming of bio-butanol for hydrogen production: effects of noble metals on bimetallic CoM/ZnO catalysts (M = Ru, Rh, Ir, Pd)

The influence of the addition of a noble metal (Ru, Rh, Ir or Pd) on the catalytic performance of Co/ZnO was studied with respect to oxidative steam reforming of the bio-butanol raw mixture (butanol/acetone/ethanol=6/3/1, mass ratio). Bimetallic catalysts, CoM/ZnO (M=Ru, Rh, Ir, Pd) had higher conversion values, decreased deactivation and higher H2 concentration in the outlet gas than monometallic Co/ZnO. However, significant differences were found in both raw mixture conversion and H2 concentrations for the different CoM/ZnO, depending on M. CoRh/ZnO presented the best catalytic behavior (65.1mol% hydrogen in the outlet after 100h of reaction at 500°C with 84% conversion). Characterization of catalysts post-reaction by Raman spectroscopy and TPO showed that less ordered and less abundant carbonaceous deposits were formed over bimetallic catalysts than over the monometallic one; CoRh/ZnO had the lowest amount of such coke.

La1−xCaxFe1−xCoxO3—a stable catalyst for oxidative steam reforming of ethanol to produce hydrogen

La1−xCaxFe1−xCoxO3 (x = 0.3, 0.5) perovskite-type oxide catalysts prepared by citric acid method were used for the steam reforming of ethanol (SRE) and oxidative steam reforming of ethanol (OSRE) to produce hydrogen. The anti-sintering and anti-coking properties of the catalysts for these two reactions have been investigated. The catalysts were characterized by temperature programmed reduction, X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy and thermal analysis techniques. The results indicated that the catalyst was highly selective to hydrogen, as well as very stable for OSRE reaction. The cobalt ions in the perovskite structure could be reduced to nanoparticles of metallic cobalt under the reduction atmosphere; the nano metallic cobalt could be oxidized and went back into the lattice of the perovskite structure under the oxidation atmosphere. The nanoparticles of metallic cobalt on the used catalyst could also be oxidized back into the perovskite structure. In the reaction process of OSRE, the cobalt species was possibly cycling as nanoparticles of metallic cobalt and cobalt ions in the perovskite structure, leading to its high anti-sintering stability.

Enhancement of hydrogen production via hydrogen peroxide as an oxidant

The performance of different Ni/Ce1−xZrxO2 (ss) catalysts of varying composition (x = 0, 0.12, 0.18 and 0.26) were investigated for hydrogen production by ethanol steam reforming (ESR). All catalysts were prepared by co-precipitation method and characterized for their surface area, pore volume, structure and morphology using different techniques (N2-BET, XRD and HRTEM). The Ce4+/Ce3+ redox couple in ceria-containing catalysts is known to be responsible for the OSC of these materials, so, the redox behaviors of these materials were investigated by EPR. Reaction parameters were optimized by varying steam to ethanol molar ratio (6, 8 and 10) in order to produce hydrogen with low carbon monoxide formation as low as possible. The minimum amounts of CO and carbon deposited are observed over Ni/CeZr-8 catalyst at 1 : 10 ethanol–water ratios. The obtained data are compared with data obtained from oxidative steam reforming of ethanol (OSRE) using hydrogen peroxide as an oxidant. The activity data indicated that hydrogen peroxide is an effective oxidant for OSRE over Ni/Ce1−xZrxO2 catalysts due to its ability to suppress CO formation and increase H2/CO ratio.

Steam reforming and oxidative steam reforming of methanol and ethanol: The behaviour of LaCo0.7Cu0.3O3

LaCo0.7Cu0.3O3 perovskite powder was prepared by means of the citrate method and treated at different temperatures from 873 to 1323K. The samples were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), temperature programmed reduction (TPR), temperature programmed desorption (TPD, O2-TPD), and scanning electron microscopy (SEM); the BET specific surface area was also determined. The reactivity of the perovskite with methanol and ethanol was investigated under steam reforming and oxidative steam reforming conditions and correlated to its chemical and structural properties. Different oxygen/alcohol molar ratios were used to study the influence of oxygen on catalytic activity and products distribution. LaCo0.7Cu0.3O3 begins to be active in alcohol steam reforming at about 523K. The catalyst calcined at 873K shows the higher conversion in methanol steam reforming. Ethanol steam reforming conversion, in contrast, is rather low and not significantly affected by the catalyst calcination temperature. The conversions increase when oxygen is present reaching 93% for methanol and 78% for ethanol. Beside the steam reforming and oxidative steam reforming, other secondary reaction paths occur: methanol decomposition and ethanol dehydrogenation.

Bio-ethanol steam reforming and autothermal reforming in 3-μm channels coated with RhPd/CeO2 for hydrogen generation

A silicon micromonolith of 7mm diameter and 0.2mm length containing 1.5 million regular channels with a diameter of 3.3μm was used for obtaining hydrogen through ethanol or bio-ethanol steam reforming (ESR) and oxidative steam reforming (OSR). The microchannels were coated with RhPd/CeO2 catalyst by a two-step method. First a CeO2 layer of ca. 100nm thickness was deposited from cerium methoxyethoxide over a SiO2 layer, which was previously grown over the silicon microchannels by oxidation. Then, noble metals were grafted over the CeO2 support from chloride precursors. The unit was successfully tested for hydrogen production, achieving hydrogen rates of 180 LH2 cmR−3 for the steam reforming of bio-ethanol at 873K, S/C=2 and 0.009s contact time. Reaction yields of 3.8 and 3.7mol hydrogen generated per mol ethanol in feed were measured for ESR and OSR, respectively. A performance comparison was performed with a conventional cordierite monolith with the same catalyst formulation. Results show for the silicon microreactor an outstanding improvement of the specific hydrogen production rate, operating at considerably reduced residence times, due to the increase in contact area per unit volume.

Oxidative steam reforming of methane to synthesis gas in microchannel reactors

Oxidative steam reforming of methane to synthesis gas (syngas) over an alumina supported bimetallic Pt–Rh catalyst was comparatively investigated in coated and packed microchannel reactors. In the first configuration, thin layers of catalysts are coated on opposite walls of a single microchannel, while the second one is described by particulate catalysts packed into an empty microchannel of dimensions identical with the first one. Both geometries are compared on the basis of methane conversion and CO selectivity measured at different values of parameters, namely reaction temperature (773–923 K), molar steam-to-carbon (S/C = 0–3.0) and oxygen-to-carbon (O2/C = 0.47–0.63) ratios in the feed, and contact time (0.36–0.71 mg min cm−3). Although methane conversions are found to be comparable, the coated catalyst gave significantly higher CO selectivities than the packed counterpart in the whole parameter range. Increase in all of the parameter values led to improvement in methane conversion, while CO selectivity increased only with temperature and contact time. Molar H2/CO ratios obtained in the coated microchannel reactor are found to vary between 1.0 and 3.0 which are at least three times smaller than those produced in the packed microchannel reactor. Catalyst deactivation is not detected in both configurations. Stable operation up to 72 h over coated microchannel verified mechanical and chemical stability of the Pt–Rh coating that produced syngas with H2/CO ratio of 2.12 at temperatures lower than employed in industrial reformers. Different flow distribution properties of coated and packed microchannels seem to play roles in affecting the product distribution.

Hydrogen production from oxidative steam reforming of bio-butanol over CoIr-based catalysts: Effect of the support

This paper studies the influence of the support on the behavior of bimetallic CoIr-based catalysts (6.5wt.% Co, 0.4wt.% Ir) for hydrogen production from the oxidative steam reforming of bio-butanol raw mixture (butanol/acetone/ethanol=6/3/1 mass ratio). Catalytic tests were carried out at 500°C for 60h with raw mixture/water/air/Ar=1/10/7.5/12 molar ratio and GHSV=7500h−1. Over CoIr/18CeZrO2 and CoIr/ZnO the main process which took place was the oxidative steam reforming of the raw mixture. CoIr/18CeZrO2 showed the better catalytic performance. Characterization of the used catalysts indicated that both active metal sintering and coke formation was prevented on the CoIr/18CeZrO2 catalyst.

Hydrogen production from yellow glycerol via catalytic oxidative steam reforming

In this research study, a low-impurity product from glycerol purification unit of a biodiesel manufacturing called yellow glycerol, was shown to be an alternative raw material for H2 generation via oxidative steam reforming reaction over Ni/CeZrO2/Al2O3 catalyst. The effects of operating parameters, such as water-to-yellow glycerol ratio between 3 and 9, reaction temperature in the range of 550–650°C, and oxygen-to-yellow glycerol ratio from 0.25 to 0.75, were explored. Partial oxidation, steam reforming and decomposition of glycerol incorporated with water gas shift reaction were the main reactions involved producing H2, CO and CO2 as the main gas products. The suitable operating condition found was at water-to-yellow glycerol ratio of 9, oxygen-to-yellow glycerol ratio of 0.5 and 650°C where nearly complete conversion of yellow glycerol was achieved with maximized hydrogen selectivity and yield at 69% and 67%, respectively. This promoted catalyst exhibited superior activity to the unpromoted Ni/Al2O3 in enhancing the main reactions producing hydrogen while strongly inhibiting coke deposition. Compared to pure glycerol, the reforming of yellow glycerol byproduct produced relatively high H2 yield, 4molH2/mol yellow glycerol vs. 4.9molH2/mol pure glycerol demonstrating that yellow glycerol is an attractive raw material for hydrogen production via the catalytic oxidative steam reforming.

Synthesis of Ce and Pr-promoted Ni and Co catalysts from hydrotalcite type precursors by reconstruction method

Catalysts were prepared from hydrotalcite type precursors using Ni, Co, and Ni–Co systems as active phases. Additionally Ce or Pr was incorporated as a promoter. The precursors were synthesized by the conventional co-precipitation method and the incorporation of Ce or Pr was carried out by reconstruction of the hydrotalcites in the presence of aqueous [Ce-EDTA]−1 or [Pr-EDTA]−1 chelates. The solids obtained were characterized by X-ray fluorescence (XRF), X-ray diffraction (XRD), temperature programmed reduction (TPR), surface area, O2− and CO2− temperature programmed desorption (TPD) and their catalytic performance was evaluated in the ethanol oxidative steam reforming reaction. The analyses demonstrate that the hydrotalcite type precursors were synthesized effectively and their thermal decomposition generated mixed oxides with a periclase type structure and spinel phases for Co-containing catalysts. It was established that the mixed Ni–Co system exhibits better redox behavior and stronger basic centers in comparison with the Ni or Co isolated system. The promoting effect of Ce or Pr was confirmed by the increase of reducibility, the strength of the basic sites, and the stability of the metallic species within the solid solution. All of the catalysts were very active and selective in the oxidative steam reforming of ethanol. In particular, the presence of the promoters produces an increase in the hydrogen and CO2 selectivity. The catalysts' performance was found to be enhanced by the simultaneous presence of Ni and Co in the catalytic system, even without redox promoters.

Effect of Platinum Incorporation on the Energetics and Oxygen Chemisorption Properties of the Ni(1 1 1) Surface

Pt makes it sustainable: Ni oxidation is an important cause of deactivation of Ni catalysts in Oxidative Steam reforming (OSR). Oxygen chemisorption is weakened on the Ni(1 1 1) surface after platinum substitution, which provides the sustainability of the Pt–Ni catalyst in OSR via preventing oxidation of Ni during the reaction

Effect of calcium dopant on catalysis of Ir/La2O3 for hydrogen production by oxidative steam reforming of glycerol

The superfluous glycerol derived from biodiesel production can be a low-cost feedstock for hydrogen production via reforming technology. In this work, a La2O3 supported iridium catalyst was employed to catalyze the oxidative steam reforming of glycerol (OSRG) for hydrogen production, in the range of S/C ratio of 1–3, C/O ratio of 0.75–1 and 550–750°C. The catalyst was modified with Na, Mg and Ca to optimize the catalytic performance in OSRG reaction. It was found that Ca is promising in promoting Ir/La2O3 catalyst for OSRG, offering excellent activity, hydrogen selectivity and stability. By combining multiple techniques, i.e. XRD, FTIR, Raman, XPS, H2-TPR, CO2-TPD and HRTEM, the Ca modified Ir/La2O3 catalyst was characterized to understand the role of Ca promoter. Multi-functions of Ca were demonstrated, including inducing structural defects of La2O2CO3, endowing the catalyst strong basicity and tuning the metal–support interaction, which make the catalyst highly resistant to coking and sintering, therefore performing excellent long-term stability for 100h.

Design and operation of a compact microchannel 5 kWel,net methanol steam reformer with novel Pt/In2O3 catalyst for fuel cell applications

A methanol reformer was designed, built and tested, which allows hydrogen production for high temperature PEM fuel cells for mobile applications applying micro-structured plate heat-exchanger technology and a novel, highly active catalyst formulation for oxidative steam reforming of methanol at temperatures exceeding 300°C. It is one of the first micro-structured methanol reformers with integrated anode off-gas combustion, which works in the kW scale. The reformer was operated under conditions of start-up, steady state and under dynamic conditions, in connection with a 1kW high temperature PEM fuel cell and finally integrated into a fuel processor, which contained an external evaporator and a heat-exchanger for super-heating the reformer feed. The thermal power of the hydrogen produced by the reformer amounted to 20kWthermal, which corresponds to 6.5kWel of a fuel cell at 40% efficiency and 80% hydrogen utilization.

Effect of noble metal on oxidative steam reforming of methanol over CuO/ZnO/Al2O3 catalysts

Noble metals of Pd, Pt, Ru and Rh were introduced into the CuO/ZnO/Al2O3(30/60/10) catalyst via incipient impregnation and co-precipitation methods to examine their effects on the oxidative steam reforming of methanol (OSRM). No obvious effect of Pd and even a negative effect of Pt were observed by incipient impregnation method. With co-precipitation, noble metals were homogeneously dispersed in CuO/ZnO/Al2O3(30/60/10) and interacted with CuO and ZnO. They improved the reducibility of the catalysts and enhanced the dissociative adsorption of methanol. Introducing Pd, Rh or Ru promoted the conversion of methanol, but enhanced the formation of CO. Depositing platinum exhibited a high conversion of methanol and a low selectivity of CO in the OSRM reaction. The promoting effect of noble metals involved facilitating the split and adsorption of H atoms during the dehydrogenation of the intermediates in OSRM.

Pd-based membrane reactors for producing ultra pure hydrogen: Oxidative reforming of bio-ethanol

A membrane reactor consisting of a dense self-supported Pd–Ag tube of wall thickness 60 μm has been filled with a Pt-based catalyst and used for producing pure hydrogen via oxidative steam reforming of bio-ethanol. The reformer feed stream consisted of water and ethanol with traces of glycerol and acetic acid in order to simulate a liquid waste of dairy industry after fermentation and concentration.The membrane reformer has been characterized through permeation and reaction tests performed at 400 and 450 °C with a reaction (lumen) pressure in the range 100–200 kPa. The hydrogen permeated through the membrane has been collected in the reactor shell by a sweep stream of nitrogen.Permeation tests verified the complete hydrogen selectivity of the thin wall tube membrane and measured permeability values at 400–450 °C of 1–2 mol m−1 s−1 Pa−0.5 accordingly to the literature.In the reaction tests, the capability of the membrane to promote the reaction conversion (shift effect) has been demonstrated. The gas chromatographic analysis of the retentate showed very low concentration of CO and the presence of methane as a main product of side-reactions. At 400 °C the pressure affects significantly the hydrogen production and the hydrogen yield moves from 0.4 to 1 when the pressure increases from 100 to 200 kPa. Significant increase of the hydrogen production has been attained at the higher temperature of 450 °C where maximum values of hydrogen yield (close to 3) have been measured with a lumen pressure of 200 kPa. Under these conditions, the technology of Pd-based membranes is effective for recovering hydrogen from a liquid waste.

Hydrogen production by oxidative steam reforming of methanol over Au/CeO2 catalysts

The production of hydrogen by oxidative steam reforming of methanol (OSRM) was investigated over a series of Au/CeO2 catalysts prepared by deposition–precipitation. The optimum operating conditions over 5wt% Au/CeO2 (calcined at 400°C, GHSV=30000mL/h-gcat, T=300°C, H2O/CH3OH molar ratio=2/1, and O2/CH3OH molar ratio=1.25/1) could be suggested to obtain 100% methanol conversion and 24.5% hydrogen yield. Additionally, the Au catalyst having an average particle size of 10.04nm and the highest amount of Au0 species (active sites for the OSRM reaction) on the catalyst support exhibited the highest activity. Based on the stability observation, the catalyst exhibited high catalytic activity over a long period, even though catalyst deactivation caused by both coke formation and sintering was found.

Hydrogen production from oxidative steam reforming of methanol: Effect of the Cu and Ni impregnation on ZrO2 and their molecular simulation studies

Cu and Ni were supported on ZrO2 by co-impregnation and sequential impregnation methods, and tested in the oxidative steam reforming of methanol (OSRM) reaction for H2 production as a function of temperature. Surface area of the catalysts showed differences as a function of the order in which the metals were added to zirconia. Among them, the Cu/ZrO2 catalyst had the lowest surface area. XRD patterns of the bimetallic catalysts did not show diffraction peaks of the Cu, Ni or bimetallic Cu–Ni alloys. In addition, TPR profiles of the bimetallic catalysts had the lowest reduction temperature compared with the monometallic samples. The reactivity of the catalysts in the range of 250–350 °C showed that the bimetallic samples prepared by successive impregnation had highest catalytic activity among all the catalysts studied. These results were also confirmed by theoretical calculations. The reactivity of the monometallic and bimetallic structures obtained by molecular simulation followed the next order: NishellCucore/ZrO2 ≅ CushellNicore/ZrO2 > Ni/Cu/ZrO2 > Cu/Ni/ZrO2 > Cu–Ni/ZrO2 > Cu/ZrO2 > Ni/ZrO2. These findings agree with the experimental results, indicating that the bimetallic catalysts prepared by successive impregnation show a higher reactivity than the Cu–Ni system obtained by co-impregnation. In addition, the selectivity for H2 production was higher on these catalysts. This result could be associated also to the presence of the bimetallic Cu–Ni and core–shell Ni/Cu nanoparticles on the catalysts, as was evidenced by TEM–EDX analysis, suggesting that the OSRM reaction may be a structure–sensitive reaction.

Hydrogen production through oxidative steam reforming of ethanol over Ni-based catalysts derived from La1−xCexNiO3 perovskite-type oxides

This paper investigates the effect of lanthanum substitution by cerium oxide on the performance of La1−xCexNiO3 (x=0, 0.05, 0.1, 0.4, 0.7 and 1.0) perovskite-type oxide precursor for the oxidative steam reforming of ethanol. All catalysts are active and selective to hydrogen but carbon deposition occurs except for La0.90Ce0.10NiO3. Increasing the Ce content decreases the amount of carbon deposited, which passes through a minimum at around 10wt% of Ce and then increases. The higher resistance to carbon formation on La0.90Ce0.10NiO3 catalyst is due to the smaller Ni crystallite size. Furthermore, the support also plays an important role on catalyst stability during ethanol conversion reaction. The reduced La0.9Ce0.1NiO3 sample exhibits the highest amount of oxygen vacancies, which decreases as ceria content increases. This highly mobile oxygen reacts with carbon species as soon as it forms, and thus keeps the metal surface free of carbon, inhibiting deactivation.