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.     

Thin‐Film Catalytic Coating of a Microreactor for Preferential CO Oxidation over Pt Catalysts

Different Pt‐based catalyst layers have been prepared and tested in a stacked foil microreactor for CO oxidation and preferential oxidation of CO in presence of hydrogen. The reactions were performed on Pt without support by impregnation of a pre‐oxidized microstructured metal plate, Pt/Al₂O₃ and Pt/CeO₂ based on sol methods as well as Pt/nano‐Al₂O₃, a combined method of sol‐gel and nanoparticle slurry coating. The ceria based sol‐gel catalyst was much more active for CO oxidation than alumina based sol‐gel catalysts at low temperature. However, total oxidation was only obtained at higher temperature on the alumina based catalysts. The combined method seems to have advantages in terms of less internal mass transfer limitation when trying to increase the catalyst coating thickness based on sol‐gel approaches due to no reduction of CO selectivity up to 300 °C reaction temperature. Experiments on CO oxidation with the Pt/CeO₂ catalyst have been conducted in an oxygen supply microreactor to evaluate the catalyst performance under sequential oxygen supply to reaction zone (CO excess).     

Low-temperature reforming of ethanol over CeO2-supported Ni-Rh bimetallic catalysts for hydrogen production

A new series of Ni-Rh bimetallic catalysts with different Ni and Rh loadings on a high-surface-area CeO₂ was developed for the reforming of bio-ethanol at low-temperature (below 450 °C) to produce H₂-rich gas for on-site or on-board fuel cell applications. Oxidative steam reforming of ethanol (OSRE) over a Ni-Rh/CeO₂ catalyst containing 5 wt% Ni and 1 wt% Rh was found to be more efficient offering about 100% ethanol conversion at 375 °C with high H₂ and CO₂ selectivity and low CO selectivity compared to the steam reforming of ethanol (SRE) reaction which required a higher temperature of about 450 °C to achieve 100% ethanol conversion. The high temperature SRE reaction favors the formation of large amount of CO, which would make the downsteam CO cleanup more complicated for polymer electrolyte membrane fuel cell (PEMFC). The presence of O₂ in the feed gas was found to greatly enhance the conversion of ethanol to produce H₂ and CO₂ as major products. Increase in Ni content above 5 wt% in the catalyst formulation decreased the H₂ selectivity while the selectivity of undesirable CH₄ and acetaldehyde increased. The 1 wt% Rh/CeO₂ catalyst was twice as active as 10 wt% Ni/CO₂ catalyst in terms of ethanol conversion and acetaldehyde selectivity and this indicated that Rh was more effective in C–C bond cleavage than Ni. The reaction was found to proceed through the formation of acetaldehyde intermediate, which subsequently underwent decomposition to produce a mixture of CO and CH₄ or reforming with H₂O and O₂ to produce CO, CO₂ and H₂. The role of Rh is mainly to cleave the C–C and C–H bonds of ethanol to produce H₂ and COx while Ni addition helps converting CO into CO₂ and H₂ by WGS reaction under the conditions employed.     

Effect of Sulfur or Nitrogen Poisoning on the Activity and Selectivity of Y-Zeolite-Supported Pt–Pd Catalysts in the Hydrogenation of Tetralin

The partial oxidation of methane (POM) to synthesis gas over SiO₂-supported Rh and Ru catalysts was studied by in situ microprobe Raman and in situ time-resolved FTIR (TR-FTIR) spectroscopies. The results of in situ microprobe Raman spectroscopic characterization indicated that no Raman band of Rh₂O₃ was detected at 500°C over the Rh/SiO₂ catalyst under a flow of a CH₄/O₂/Ar (2/1/45, molar ratio) mixture, while the Raman bands of RuO₂ can even be detected at 600°C over the Ru/SiO₂ catalyst under the same atmosphere. The experiments of in situ TR-FTIR spectroscopic characterizations on the reactions of CH₄ over O₂ pre-treated Rh/SiO₂ and Ru/SiO₂ catalysts indicated that the products of CH₄ oxidation over Rh/SiO₂ and Ru/SiO₂ greatly depend on the concentration of O²– species over the catalysts. On the catalysts with high concentration of O²–, CH₄ will be completely oxidized to CO₂. However, if the concentration of O²– species over the catalysts is low enough, CH₄ can be selectively converted to CO without the formation of CO₂. The parallel experiments using in situ TR-FTIR spectroscopy to monitor the reaction of the CH₄/O₂/Ar (2/1/45, molar ratio) mixture over Rh/SiO₂ and Ru/SiO₂ catalysts show that the mechanisms of synthesis gas formation over the two catalysts are quite different. On the Rh/SiO₂ catalyst, synthesis gas is mainly formed by the direct oxidation of CH₄, while on the Ru/SiO₂ catalyst, the dominant pathway of synthesis gas formation is via the sequence of total oxidation of CH₄ followed by reforming of unconverted CH₄ with CO₂ and H₂O. The significant difference in the mechanisms of partial oxidation of CH₄ to synthesis gas over Rh/SiO₂ and Ru/SiO₂ catalysts can be well related to the difference in the concentration of O²– species over the catalysts under the reaction conditions mainly due to the difference in oxygen affinity of the two metals.     

Role of the surface state of Ni/Al2O3 in partial oxidation of CH4

The effect of gas phase O₂ and reversibly adsorbed oxygen on the decomposition of CH₄ and the surface state of a Ni/Al₂O₃ catalyst during partial oxidation of CH₄ were studied using the transient response technique at atmospheric pressure and 700°C. The results show that, when the catalyst surface is completely oxidized under experimental conditions, only a small amount of CO and H₂ can be produced from non‐selective oxidation of CH₄ by reversibly adsorbed oxygen which is more active in oxidizing CH₄ completely than NiO via the Rideal–Eley mechanism and both the conversions of CH₄ and O₂ and the selectivities to CO and H₂ are very low. Therefore, keeping the catalyst surface in the reduced state is the precondition of high conversion of CH₄ and high selectivities to CO and H₂. The surface state of the catalyst decides the reaction mechanism and plays a very important role in the conversions and selectivities of partial oxidation of CH₄. During partial oxidation of CH₄, no oxygen species but a small amount of carbon exists on the catalyst surface, which is favorable for maintaining the catalyst in the reduced state and the selectivity of CO. The results also indicate that direct oxidation is the main route for partial oxidation of CH₄, and the indirect oxidation mechanism is not able to gain dominance in the reaction under the experimental conditions. This revised version was published online in July 2006 with corrections to the Cover Date.     

Highly hydrogen-deficient hydrocarbon species for the CO2-reforming of CH4 on Co/Al2O3 catalyst

The dynamics of produced CO and H₂, measured by pulse surface reaction rate analysis (PSRA), revealed that the intermediate hydrocarbon species for the CO₂-reforming of CH₄ was highly hydrogen-deficient (CH_0.75) on supported Co/Al₂O₃ catalyst. It was also found that the species was more reactive than the less hydrogen-deficient one (CH_2.4) on Ni/Al₂O₃ catalyst.     

Transient response of catalyst bed temperature in the pulsed reaction of partial oxidation of methane to synthesis gas over supported group VIII metal catalysts

Mechanisms of partial oxidation of methane to synthesis gas were studied using a pulsed reaction technique and temperature jump measurement. Catalyst bed temperatures were directly measured by introducing 1 and 3 ml pulses of a mixture of CH₄ and O₂ (2/1). With Ir, Pt and Ni/TiO₂ catalysts, a sudden temperature increase at the front edge of the catalyst bed was observed upon introduction of the pulse. The synthesis gas production basically proceeded via two-step paths consisting of highly exothermic complete methane oxidation to give H₂O and CO₂, followed by the endothermic reforming of methane with H₂O and CO₂. In contrast, with the Rh and Pd/TiO₂ catalysts, the temperature at the front edge of the catalyst bed decreased upon introduction of the CH₄/O₂ (2/1) pulse and a small increase in the temperature at the rear end was observed. Initially, the endothermic decomposition of CH₄ to H₂ and deposited carbon or CH_x probably took place at the front edge of the catalyst bed, after which the deposited carbon or generated CH_x species would be oxidized into CO_x. When the Ru/TiO₂ catalyst was used, a temperature increase at the front edge of the catalyst bed was observed upon introduction of the 3 ml pulse of CH₄/O₂. In contrast, the temperature drop at the front edge of the catalyst bed was observed for a 1 ml pulse of CH₄/O₂. These results seemed to exhibit two possibilities for a synthesis gas formation route over the Ru/TiO₂ catalyst. The reaction pathway of the partial oxidation of methane with group VIII metal-loaded catalysts depended strongly upon the metal species and reaction conditions.     

Ni‐Al2O3/Ni‐foam catalyst with enhanced heat transfer for hydrogenation of CO2 to methane

Monolithic Ni‐Al₂O₃/Ni‐foam catalyst is developed by modified wet chemical etching of Ni‐foam, being highly active/selective and stable in strongly exothermic CO₂ methanation process. The as‐prepared catalysts are characterized by x‐ray diffraction scanning electron microscopy, inductively coupled plasma atomic emission spectrometry, and H₂‐temperature programmed reduction‐mass spectrometry. The results indicate that modified wet chemical etching method is working efficiently for one‐step creating and firmly embedding NiO‐Al₂O₃ composite catalyst layer (～2 μm) into the Ni‐foam struts. High CO₂ conversion of 90% and high CH₄ selectivity of >99.9% can be obtained and maintained for a feed of H₂/CO₂ (molar ratio of 4/1) at 320°C and 0.1 MPa with a gas hourly space velocity of 5000 h^?1, throughout entire 1200 h test over 10.2 mL such monolithic catalysts. Computational fluid dynamics calculation and experimental measurement consistently confirm a dramatic reduction of “hotspot” temperature due to enhanced heat transfer. © 2015 American Institute of Chemical Engineers AIChE J, 61: 4323–4331, 2015     

Oxidative reforming of methane on structured Ni-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/cordierite catalysts

The catalytic properties of Ni/Al₂O₃ composites supported on ceramic cordierite honeycomb monoliths in oxidative methane reforming are reported. The prereduced catalyst has been tested in a flow reactor using reaction mixtures of the following compositions: in methane oxidation, 2–6% CH₄, 2–9% O₂, Ar; in carbon dioxide and oxidative carbon dioxide reforming of methane, 2–6% CH₄, 6–12% CO₂, and 0–4% O₂, and Ar. Physicochemical studies include the monitoring of the formation and oxidation of carbon, the strength of the Ni-O bond, and the phase composition of the catalyst. The structured Ni-Al₂O₃ catalysts are much more productive in the carbon dioxide reforming of methane than conventional granular catalysts. The catalysts performance is made more stable by regulating the acid-base properties of their surface via the introduction of alkali metal (Na, K) oxides to retard the coking of the surface. Rare-earth metal oxides with a low redox potential (La₂O₃, CeO₂) enhance the activity and stability of Ni-Al₂O₃/cordierite catalysts in the deep and partial oxidation and carbon dioxide reforming of methane. The carbon dioxide reforming of methane on the (NiO + La₂O₃ + Al₂O₃)/cordierite catalyst can be intensified by adding oxygen to the gas feed. This reduces the temperature necessary to reach a high methane conversion and does not exert any significant effect on the selectivity with respect to H₂.     

Partial oxidation of methane and the effect of sulfur on catalytic activity and selectivity

Partial oxidation of methane into syngas was conducted over fresh and sulfided catalysts at a temperature range of 450–750 °C. The temperature dependence of conversion, H₂/CO ratio, and the CO₂ concentration were measured for both fresh and sulfided catalysts. Regardless of metal type, metal loading, support type, and the methods of preparation it appears that all the fresh catalysts were very active and conversions of higher than 70% with H₂/CO ratio of about 2 were observed at 750 °C. Pulse sulfidation appears to be reversible for some of the catalysts but not for all. Under pulse sulfidation conditions, the Rh(0.5%)/Al₂O₃ and NiMg₂O_x-1100 °C (solid solution) catalysts were fully regenerated after reduction with hydrogen. Rh catalyst showed the best overall activity, less carbon deposition, both fresh and when it was exposed to pulses of H₂S. Sulfidation under steady-state conditions, flowing H₂S/Ar mixture over the catalysts, significantly reduce catalyst activity. The catalysts were characterized before and after reaction with H₂S using temperature-programmed oxidation (TPO) and reduction (TPR), X-ray diffraction, and XPS.     

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.     

A study of methane partial oxidation in annular reactor: activity of Rh/α-Al2O3 and Rh/ZrO2 catalysts

The activity of Rh/α-Al₂O₃ and Rh/ZrO₂ in CH₄ partial oxidation was investigated in an annular reactor, which operates at high space velocity, under kinetically controlled conditions and minimum temperature gradients along the catalyst bed. The effects of temperature, dilution, space velocity and CH₄/O₂ ratio were explored. Rh/α-Al₂O₃ provided higher H₂ yields than Rh/ZrO₂ at all conditions. Concerning the process kinetics, over Rh/α-Al₂O₃ an indirect-consecutive kinetic scheme for synthesis gas formation prevailed; the observed trends were in fact in line with the combined presence of methane total oxidation, methane reforming reactions and consecutive oxidations of H₂ and CO. Over Rh/ZrO₂ the additional contribution of a direct route to synthesis gas could not be excluded. The complexity of the reaction scheme seems associated with the existence of different active sites, whose concentration could be affected by metal-support interactions and Rh reconstruction during conditioning. Indeed, once exposed to the reaction atmosphere, the fresh catalysts showed an initial conditioning during which a specific activation of the high temperature routes (responsible for H₂ production) was observed.     

Conversion of greenhouse gases into syngas via combined effects of discharge activation and catalysis

The topics on conversion and utilization of methane and carbon dioxide are important issues in tackling the global warming effect from the two greenhouse gases. In the present study, pure plasma and plasma catalytic activation of methane and carbon dioxide were investigated for syngas production. For pure plasma process, the effects of discharge power, CH₄/CO₂ ratios in the feed, total flow rate, as well as the concentration of the balanced gas of Ar were studied. Ar in the feed has great effects on the conversion and the stability of the reaction. At 120 °C and atmospheric pressure, the conversion of CH₄ increased from 39% to 56% and that of CO₂ increased from 23% to 30% when the Ar content in the feed increased from 0% to 50%, whereas Ar showed little effect on the H₂/CO ratios in the products. Moreover, the conversions of CH₄ and CO₂ remained unchanged within the testing hours in the presence of 50% of Ar, which was contrastive with those obtained without Ar in the feed. When Cu–Ni/Al₂O₃ catalyst was filled in the discharge gap at 450 °C, the synergism between the catalyst and dielectric-barrier discharge (DBD) plasma was achieved. Conversions of CH₄ for plasma alone, plasma-catalysis and catalysis alone were 13%, 69% and 10%, respectively. Selectivities to CO and H₂ under the plasma-catalytic process were, respectively, 76% and 57%.     

Hydrogen Production from Methane and Carbon Dioxide by Catalyst-Assisted Chemical Looping

Hydrogen can be produced from a mixture of CH₄ and CO₂, based on chemical looping techniques. A physical mixture of a Ni/Al₂O₃ catalyst and Fe₂O₃?CCeZrO₂ as oxygen storage material is used in the chemical looping. During the reduction step, CH₄/CO₂ is converted over Ni/Al₂O₃ into syngas, which then reduces iron oxide, giving CO₂ and H₂O. During re-oxidation of the oxygen storage material by steam, H₂ with ppm levels of CO_x is produced.     

CO2 conversion through combined steam and CO2 reforming of methane reactions over Ni and Co catalysts

Ni‐Co bimetallic and Ni or Co monometallic catalysts prepared for CO₂ reforming of methane were tested with the stimulated biogas containing steam, CO₂, CH₄, H₂, and CO. A mix of the prepared CO₂ reforming catalyst and a commercial steam reforming catalyst was used in hopes of maximizing the CO₂ conversion. Both CO₂ reforming and steam reforming of CH₄ occurred over the prepared Ni‐Co bimetallic and Ni or Co monometallic catalysts when the feed contained steam. However, CO₂ reforming did not occur on the commercial steam reforming catalyst. There was a critical steam content limit above which the catalyst facilitated no more CO₂ conversion but net CO₂ production for steam reforming and water‐gas shift became the dominant reactions in the system. The Ni‐Co bimetallic catalyst can convert more than 70% of CO₂ in a biogas feed that contains ~33 mol% of CH₄, 21.5 mol% of CO₂, 12 mol% of H₂O, 3.5 mol% of H₂, and 30 mol% of N₂. The H₂/CO ratio of the produced syngas was in the range of 1.8‐2. X‐ray absorption spectroscopy of the spent catalysts revealed that the metallic sites of Ni‐Co bimetallic, Ni and Co monometallic catalysts after the steam reforming of methane reaction with equimolar feed (CH₄:H₂O:N₂ = 1:1:1) experienced severe oxidation, which led to the catalytic deactivation.     

Steam reforming of liquid hydrocarbon fuels for micro-fuel cells. Pre-reforming of model jet fuels over supported metal catalysts

The present work deals with pre-reforming of logistic hydrocarbon fuel (jet fuel) as a part of an integrated approach to developing an on-board fuel reformer for use in a micro-solid-oxide fuel cell system. The purpose of doing pre-reforming is to ensure carbon-free reformulation of JP-8 jet fuel into hydrogen and carbon monoxide for use in a micro-solid-oxide fuel cell. Several model jet fuels have been tested for the pre-reforming at low temperature (450–550 °C) in a lab-scale reforming reactor. Proper temperature control and pre-mixing of feed fuels and steam have been found to be important for the prevention of coke formation prior to pre-reforming. Both noble metal and base-metal catalysts have been prepared and tested. As compared with an Al₂O₃-supported Ni catalyst, supported Rh catalysts show not only high activity but also high resistance to deactivation due to carbon formation. Removal of residual Cl⁻ from Rh/CeO₂–Al₂O₃ improves the metal dispersion and the pre-reforming activity. The reformates from the current pre-reformer contain mainly CH₄, CO, H₂, in which CH₄ can be further converted to H₂ and CO by subsequent main-reforming.     

Nickel Oxide Based Supported Catalysts for the In-situ Reactions of Methanation and Desulfurization in the Removal of Sour Gases from Simulated Natural Gas

Supported nickel oxide based catalysts were prepared by wetness impregnation method for the in-situ reactions of H₂S desulfurization and CO₂ methanation from ambient temperature up to 300 °C. Fe/Co/Ni (10:30:60)–Al₂O₃ and Pr/Co/Ni (5:35:60)–Al₂O₃ catalysts were revealed as the most potential catalysts, which yielded 2.9% and 6.1% of CH₄ at reaction temperature of 300 °C, respectively. From XPS, Ni₂O₃ and Fe₃O₄ were suggested as the surface active components on the Fe/Co/Ni (10:30:60)–Al₂O₃ catalyst, while Ni₂O₃ and Co₃O₄ on the Pr/Co/Ni (5:35:60)–Al₂O₃ catalyst.     

Kinetic study of the catalytic reforming of methane with carbon dioxide to synthesis gas over Ni/La2O3 catalyst

The kinetic behavior of the Ni/La₂O₃ catalyst in the reforming reaction of methane with carbon dioxide was investigated as a function of temperature and partial pressures of CH₄ and CO₂. The apparent activation energy of the reforming reaction was estimated to be 13.2 kcal/mol. It was also found that increase of the H₂ partial pressure leads to a continuous enhancement of the rate of CO formation, due to the simultaneous occurrence of the water-gas shift reaction. The mechanism of the CH₄/CO₂ reaction has been investigated using steady-state isotopic tracing and transient experiments, as well as FTIR, XRD, XPS and HR-TEM techniques. Based on the mechanistic results, a kinetic model was developed, which was found to predict satisfactorily the kinetic measurements. Methane cracking and the surface reaction between C and oxycarbonate species, are suggested to be the rate determining steps of the CH₄/CO₂ reaction over the Ni/La₂O₃ catalyst.     

One‐step production of CO‐ and CO2‐free hydrogen from biomass

The reaction between a biomass (cellulose, sucrose, glucose, starch, cotton, or Japanese paper) and NaOH in the presence of water vapor produced pure hydrogen without CO and CO₂ at temperatures in the range 473–623K. The addition of Ni/Al₂O₃ or Rh/Al₂O₃ catalyst to cellulose enhanced the production of hydrogen at <573 K. The reaction between cellulose and NaOH can be written as: C₆H₁₀O₅ + 12NaOH + H₂O = 6Na₂CO₃ + 12H₂. The reactivities of alkali metal hydroxides were: KOH > NaOH ? LiOH. Copyright © 2004 Society of Chemical Industry     

Improvement of coke resistance of Ni/Al2O3 catalyst in CH4/CO2 reforming by ZrO2 addition

This work investigates the improvement of Ni/Al₂O₃ catalyst stability by ZrO₂ addition for H₂ gas production from CH₄/CO₂ reforming reactions. The initial effect of Ni addition was followed by the effect of increasing operating temperature to 500–700 °C as well as the effect of ZrO₂ loading and the promoted catalyst preparation methods by using a feed gas mixture at a CH₄:CO₂ ratio of 1:1.25. The experimental results showed that a high reaction temperature of 700 °C was favored by an endothermic dry reforming reaction. In this reaction the deactivation of Ni/Al₂O₃ was mainly due to coke deposition. This deactivation was evidently inhibited by ZrO₂, as it enhances dissociation of CO₂ forming oxygen intermediates near the contact between ZrO₂ and nickel where the deposited coke is gasified afterwards. The texture of the catalyst or BET surface area was affected by the catalyst preparation method. The change of the catalyst texture resulted from the formation of ZrO₂–Al₂O₃ composite and the plugging of Al₂O₃ pore by ZrO₂. The 15% Ni/10% ZrO₂/Al₂O₃ co-impregnated catalyst showed a higher BET surface area and catalytic activity than the sequentially impregnated catalyst whereas coke inhibition capability of the promoted catalysts prepared by either method was comparable. Further study on long-term catalyst stability should be made.