Ethanol steam reforming for hydrogen generation over structured catalysts

The present paper reports on the preparation, characterization and reaction evaluation of structured catalysts toward hydrogen generation via ethanol steam reforming. To these ends, 400 cpsi cordierite monoliths were functionalized with Rh–Pd/CeO₂ catalyst. SEM, TEM and XRD showed a uniform and well-covering CeO₂ layer where Rh–Pd nanoparticles of less than 0.5 nm were anchored. The functionalized monoliths were successfully tested for synthesis gas production from ethanol steam reforming. Realistic operating conditions were selected, including temperatures between 500 and 950 K, pressures from 1 to 6 bar, undiluted ethanol:water molar ratios 1:4–1:8 (i.e., 2 ≤ S/C ≤ 4) and a wide range of feed loads. Appropriate activity and hydrogen selectivity were verified for the catalytic system, with ca. complete ethanol conversion at T > 700 K and a minor, or even negligible, generation of by-products (acetaldehyde, acetone, ethane, ethylene). Operating at 950 K and 1.5 bar, a H₂ yield of 3.4 mol hydrogen per mol ethanol in feed was achieved for a liquid feed load of 0.22 μl_liq/(mg_cat min) (S/C = 3), with 8.1% of CH₄ and 8.2% of CO on dry basis. Kinetic parameters of a phenomenological set of reaction rate equations were fitted against experimental data, considering ethanol decomposition (methane formation) with subsequent methane steam reforming to both CO and CO₂ and water–gas shift reaction.     

Oxidative steam reforming of ethanol over Rh based catalysts in a micro-channel reactor

Oxidative steam reforming of ethanol (OSRE) was studied over Rh/CeO₂/Al₂O₃ catalysts in a micro-channel reactor. First, the catalyst support, Al₂O₃, was deposited on to the metallic substrate by washcoating and then the CeO₂ and active metal were sequentially impregnated. The effect of support composition as well as active metal composition on oxidative steam reforming of ethanol in a micro-channel reactor was studied at atmospheric pressure, with water to ethanol molar ratio of 6 and oxygen to ethanol molar ratio ranging from 0.5 to 1.5, over a temperature range of 350-550 °C. Ceria added to 1%Rh/Al₂O₃ showed higher activity and selectivity than 1%Rh/Al₂O₃ alone. Out of the various catalysts tested, 2%Rh/20%CeO₂/Al₂O₃ performed well in terms of activity, selectivity and stability. The OSRE performance was compared with that of SRE over 2%Rh/20%CeO₂/Al₂O₃ catalyst at identical operating conditions. Compared to SRE, the activity in OSRE was higher; however the selectivity to desired products was slightly lower. The H₂ yield obtained in OSRE was ∼112 m³ kg⁻¹ h⁻¹, as compared to ∼128 m³ kg⁻¹ h⁻¹ in SRE. The stability test performed on 2%Rh/20%CeO₂/Al₂O₃ at 500 °C for OSRE showed that the catalyst was stable for ∼40 h and then started to deactivate slowly. The comparison between packed bed reactor and micro-channel reactor showed that the micro-channel reactor can be used for OSRE to produce hydrogen without any diffusional effects in the catalyst layer.     

Ethanol steam reforming and water gas shift over Co/ZnO catalytic honeycombs doped with Fe,Ni, Cu,Cr and Na

The effect of Fe, Ni, Cu, Cr, and Na (1%) addition over ZnO-supported Co (10%) honeycomb catalysts in the steam reforming of ethanol (ESR) and water gas shift reaction (WGS) for the production of hydrogen was studied. HRTEM and EEL spectroscopy revealed the formation of metal alloys between Co and Fe, Ni, Cu, and Cr. Catalysts promoted with Fe and Cr performed better in the ESR, and the sample promoted with Fe showed high activity for WGS at low temperature. As deduced from TPR and oxidation pulse experiments, alloy particles in catalysts promoted with Fe and Cr exhibited a rapid and higher degree of redox exchange between reduced and oxidized Co, which may explain the better catalytic performance.     

CFD study of heat and mass transfer in ethanol steam reforming in a catalytic membrane reactor

This work shows the analysis of ethanol steam reforming process within a catalytic membrane reactor. A 2-D non-isothermal CFD model was developed using Comsol Multiphysics, based on previous experimentally validated isothermal model. A comprehensive heat and mass transfer study was carried out utilizing the model. Operating conditions such as liquid hourly space velocity (LHSV) (3.77–37.7 h^?1), temperature (673–823 K), reaction side pressure (4–10 bar) and permeate side sweep gas flow pattern were discussed. A temperature gradient along the reactor was observed from the model and a “cold spot” was seen at the reactor entrance area, which is unfavorable for the highly endothermic ethanol steam reforming process. By changing the sweep gas pattern to counter-current, the “cold spot” appears to be smaller with a reduced temperature drop. By studying the individual reaction rates, reverse methane steam reforming (methanation) was observed, caused by the low temperature in the “cold spot”. Optimal operating conditions were found to be under LHSV = 37.7 h^?1 and counter-current sweep gas conditions.     

An analytical and experimental investigation of high-pressure catalytic steam reforming of ethanol in a hydrogen selective membrane reactor

The objective of this work was to explore the benefits of high-pressure steam reforming of ethanol for the production of hydrogen needed to refuel the high-pressure tanks of fuel cell (polymer electrolyte) vehicles. This paper reports on the potential efficiency benefits and challenges of pressurized reforming and options for dealing with the challenges; it reports the results from experiments in a micro-reactor, followed by a modeling study of the reactor to project the dependence of the hydrogen yields on process parameters. The experiments were conducted in the range of approximately 7–70 atm, 600–750 °C, steam-to-carbon molar ratios of 3–12, and gas hourly space velocities of 8500–83,000 per hour. By placing a hydrogen-transporting palladium-alloy membrane within the catalyst zone, this study quantified the beneficial effect of hydrogen extraction from the reforming zone. The model was used to explore the parameter space to define the reactor and conditions that would be needed to approach the efficiency targets for distributed hydrogen production plants. The results indicate that the tested catalyst was sufficiently active, and the hydrogen yield achieved with the experimental membrane reactor was limited by the low hydrogen flux of the tested membrane. The reactor model predicts that a membrane with at least 20 times higher flux than currently evaluated would be sufficient to generate hydrogen yields to match efficiency targets of 72%.     

Oxidative steam reforming of ethanol over a Pt/Al2O3 catalyst in a Pd-based membrane reactor

In this study, the ability of a Pd-Ag membrane reactor of producing ultrapure hydrogen via oxidative steam reforming of ethanol has been evaluated. A self supported Pd-Ag tube of wall thickness 60 μm has been filled with a commercial Pt-based catalyst and assembled into a membrane module in a finger-like configuration. In order to evaluate the hydrogen yield behavior under different operating conditions, experimental tests have been performed at temperatures of 400 and 450 °C and pressures of 150 and 200 kPa. The oxidative steam reforming of ethanol has been carried out by feeding the membrane reactor with a gas stream containing a dilute water-ethanol mixture and air. Different water/ethanol feed flow rates (5, 10, 15 g h⁻¹), several water/ethanol (4, 10, 13) and oxygen/ethanol (0.3, 0.5, 0.7) feed molar ratios have been tested. The results pointed out that the highest hydrogen yield (moles of permeated hydrogen per mole of ethanol fed) corresponding to almost 4.1 has been attained at 450 °C and 200 kPa of lumen pressure by using a water/ethanol/oxygen feed molar ratio of 10/1/0.5.The results of these tests have been compared with those reported for the ethanol steam reforming in a Pd-Ag membrane reactor filled with the same Pt-based catalyst. This comparison has shown a positive effect on the hydrogen yield of small oxygen addition in the feed stream.     

Evaluation of a micro-channel reactor for steam reforming of ethylene glycol: A comparative study of catalytic activity of Pt or/and Ni supported γ-alumina catalysts

Steam reforming of ethylene glycol (EG) was studied using γ-alumina supported 12%Ni, 3%Pt and 3%Pt12%Ni catalysts, in a micro-channel reactor. The parallel micro-channels were etched on a stainless steel plate using micro-milling technique with high speed CNC machine. The catalysts were prepared by the incipient wetness impregnation method and were characterized by using XRD, BET, FE-SEM, H₂-TPR and TGA analyses. The effects of reaction temperature and feed flow rate on the EG conversion, hydrogen yield and selectivities of the gaseous products were investigated. Experimental findings revealed that 3%Pt12%Ni/γ-alumina catalyst can provide the highest EG conversion (96.1%) with 76.6% hydrogen yield and 5.3% CO selectivity at 450 °C temperature and 4 mL h^?1 feed flow rate. Furthermore, continuous EG steam reforming identified 3%Pt12%Ni/γ-alumina as the most stable catalyst. This catalyst can remain stable after being on stream for more than 20 h.     

Coke deactivation of Ni and Co catalysts in ethanol steam reforming at mild temperatures in a fluidized bed reactor

The deactivation by coke deposition of Ni and Co catalysts in the steam reforming of ethanol has been studied in a fluidized bed reactor under the following conditions: 500 and 700 °C; steam/ethanol molar ratio, 6; space time, 0.14 g_catalyst h/g_ethanol, partial pressure of ethanol in the feed, 0.11 bar, and time on stream up to 20 h. The decrease in activity depends mainly on the nature of the coke deposited on the catalysts, as well as on the physical–chemical properties (BET surface area, pore volume, metal surface area) of the catalysts. At 500 °C (suitable temperature for enhancing the WGS reaction, decreasing energy requirements and avoiding Ni sintering), the main cause of deactivation is the encapsulating coke fraction (monoatomic and polymeric carbon) that blocks metallic sites, whereas the fibrous coke fraction (filamentous carbon) coats catalyst particles and increases their size with time on stream with a low effect on deactivation, especially for catalysts with high surface area. The catalyst with 10 wt% Ni supported on SiO₂ strikes a suitable balance between reforming activity and stability, given that both the capability of Ni for dehydrogenation and C–C breakage and the porous structure of SiO₂ support enhance the formation of filamentous coke with low deactivation. This catalyst is suitable for use at 500 °C in a fluidized bed, in which the collision among particles causes the removal of the external filamentous coke, thus minimizing the pore blockage of the SiO₂. At 700 °C, the coke content in the catalyst is low, with the coke being of filamentous nature and with a highly graphitic structure.     

Study on a catalytic membrane reactor for hydrogen production from ethanol steam reforming

Ethanol steam reforming in a membrane reactor with catalytic membranes was investigated to achieve important aims in one process, such as improvement in ethanol conversion and hydrogen yield, high hydrogen recovery and CO reduction. In order to confirm the efficiency of reaction and CO reduction, an ethanol reforming-catalytic membrane reactor with water–gas shift reaction (ECRW) in the permeate side was compared with a conventional reactor (CR) and an ethanol reforming-catalytic membrane reactor (ECR). In comparison with the CR, ethanol conversion improvement of 11.9–19% and high hydrogen recovery of 78–87% were observed in the temperature range of 300–600 °C in the ECRW. Compared with CR and ECR, the hydrogen yield of ECRW increased up to 38% and 30%, respectively. Particularly, the ECRW showed higher hydrogen yield at high temperature, because Pt/Degussa P25 loaded in the permeate side showed catalytic activity for the methane steam reforming as well as WGS reaction. Moreover, CO concentration was reduced under 1% by the WGS reaction in the permeate side in the temperature range of 300–500 °C.     

Theoretical study of hydrogen production by ethanol steam reforming: Technical evaluation and performance analysis of catalytic membrane reactor

Ethanol steam reforming over a Co/Al₂O₃ catalyst was studied theoretically in a catalytic PdAg membrane reactor (CMR). A mathematical model has been developed to elucidate the behavior of CMR by taking into account the chemical reactions, heat and mass transfer phenomena. The effect of operating parameters on the performance of CMR has been evaluated in terms of ethanol conversion, hydrogen recovery and hydrogen yield. The results revealed the high performance of this configuration is related to the continuous removal of hydrogen from the retentate side, shifting the reaction equilibrium towards hydrogen formation. Sensitivity analysis of operating parameters indicate that ethanol conversion is favored at higher temperatures, pressures, sweep ratios and feed molar ratios. Moreover, increasing the feed molar ratio enhances the ethanol conversion, and decreases the hydrogen recovery due to reduction of partial pressure of hydrogen and consequently decreasing the driving force for the hydrogen permeation through the membrane.     

Catalysts based on Co-Birnessite and Co-Todorokite for the efficient production of hydrogen by ethanol steam reforming

Two structured manganese oxides (Birnessite and Todorokite) containing Co have been studied in the steam reforming of ethanol. It has been found that both materials are active in the hydrogen production, exhibiting high values of conversion of ethanol and selectivities to hydrogen (100% and 70%, respectively). The best results have been obtained with the catalyst based on Todorokite material. Characterization by DRX, BET area, TPR and TEM has allowed to find that the excellent performance exhibited by this material could be attributed to the lower size of the Co metallic particles present in this sample (6 nm vs 12 nm in Birnessite). This lower size could be related to the especial microporous structure of Todorokite precursor, which could provide high-quality positions for the stabilization of the Co metal particles during calcination and reduction steps. Catalytic deactivation has also been considered. Deactivation was found higher for Todorokite-based catalyst, which presented the largest amount of deposited carbon (26.2 wt% for Co-TOD vs 10.6 wt% for Co-BIR). On the other hand, the degree of metal sintering was found similar in both catalysts. Therefore, the deactivation of the catalysts has been attributed primarily to the deposition of coke. The results presented here show that it is possible to prepare new catalysts based on manganese oxides with Birnessite and Todorokite structure and promoted with Co with high catalytic performance in the steam reforming of ethanol.     

Comparative study of propane steam reforming in vanadium based catalytic membrane reactor with nickel-based catalysts

The performance of catalytic membrane reactor with Pd-coated V membrane was examined for steam reforming of propane. The long term reforming experiment confirmed the stability of the V membrane with high hydrogen selectivity and permeability. The effect of types of hydrogen permeable membranes on the performance of the catalytic membrane reactor was studied by comparing Pd-coated V, Pd–23Ag, and Pd–10Ag membranes. The types of hydrogen separation membranes (i.e. hydrogen removal rates) did not have a marked effect on the propane conversion rates, while the product compositions were largely influenced by the hydrogen removal rate. Varying metal oxide supports of Ni-catalysts resulted in significant differences in the product compositions. Further, the evaluation of various catalyst-support systems (9wt%Ni–1wt%M/CeO₂, M = Co, Pt, Ag, Ru) revealed that hydrogen yield was the highest when 1wt%Ag was added to Ni/CeO₂. However, it was also found that excessive secondary metal additions can have negative impact on the catalytic behaviour of parent catalysts.     

Ethanol steam reforming reaction in a porous stainless steel supported palladium membrane reactor

In this experimental work, the ethanol steam reforming reaction is performed in a porous stainless steel supported palladium membrane reactor with the aim of investigating the influence of the membrane characteristics as well as of the reaction pressure. The membrane is prepared by electroless plating technique with the palladium layer around 25 μm deposited onto a stainless steel tubular macroporous support. The experimental campaign is directed both towards permeation and reaction tests. Firstly, pure He and H₂ are supplied separately between 350 and 400 °C in the MR in permeator modality for calculating the ideal selectivity αH₂/He. Thus, the MR is packed with 3 g of a commercial Co/Al₂O₃ catalyst and reaction tests are performed at 400 °C, by varying the reaction pressure from 3.0 to 8.0 bar. Experimental results in terms of ethanol conversions as well as recovery and purity of hydrogen are given and compared with some results in the same research field from the open literature.As best result of this work, 100% ethanol conversion is reached at 400 °C and 8 bar, recovering a hydrogen-rich stream consisting of more than 50% over the total hydrogen produced from reaction, having a purity around 65%.