Cobalt-based nanoparticles as catalysts for low temperature hydrogen production by ethanol steam reforming

Results obtained in the synthesis, characterization and application as catalyst of cobalt nanoparticles are reported. Cobalt nanoparticles were prepared via reduction method in aqueous solution. Structural characterization was carried out using X-ray diffraction (XRD), morphological studies were performed with a scanning electron microscope equipped with a field emission gun (FE-SEM). A DC-superconducting quantum interference device “SQUID” magnetometer was used to measure the room temperature (RT) magnetic hysteresis cycle in the −5 ÷ 5 Tesla (T) μ₀H magnetic field range as well as magnetization as a function of temperature. This material is constituted by very small primary particles (∼2.8 nm radius) which appear amorphous to XRD and have a superparamagnetic behaviour. However, annealing at 773 K and also utilization in the catalytic reactor at the same temperature result in XRD detectable cubic Co nanocrystals. These unsupported cobalt nanoparticles were found catalytically active in the ethanol steam reforming reaction, producing hydrogen with 90% yield at 773 K. These nanoparticles show a better catalytic behaviour compared to those of more conventional Co and Ni based catalysts, due to very low CO and methane production, and with moderate formation of carbonaceous materials.     

Hydrogen generation via ethanol steam reforming over Co/HAp catalysts

The catalytic activity of calcium hydroxyapatite (HAp) supported cobalt nanoparticles in ethanol steam reforming (SRE) was investigated. Co was supported on hydrothermally prepared HAp by incipient wetness impregnation method. Co/HAp catalysts were characterized through XRD, FT-IR and Raman spectroscopy, TEM, SEM/EDS, N₂ physisorption, TG and TPR-H₂. Results showed that spinel cobalt oxide is reduced to CoO and Co and these species are responsible for catalytic activity for hydrogen production via SRE process. The main reactions over Co/HAp are incomplete steam reforming and dehydrogenation of ethanol. Reforming experiment over pre-reduced sample indicated a negative impact of H₂ treatment on hydrogen production. The best catalytic properties (${\text{Y}}_{{\text{H}}_2}$ and C_EtOH) were obtained over 5%Co/HAp catalyst.     

Redox properties of Co- and Cu-based catalysts for the steam reforming of ethanol

Co- and Cu-based catalysts prepared by means of a flame pyrolysis (FP) technique are proposed as possible substitutes for Ni-based catalysts, very active for the Ethanol Steam Reforming reaction, but showing poor stability towards coke formation when operating at relatively low temperature.     

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.     

Hydrogen production by ethanol steam reforming: A study of Co- and Ce-based catalysts over FeCrAlloy monoliths

Co- and Ce-based structured catalysts deposited on FeCrAlloy monoliths have been prepared. A new two-step strategy for coating the monolith is used: (i) first, a MgAl₂O₄ spinel layer is generated on the FeCrAlloy substrate, and (ii) then, Co and Ce are incorporated in two different molar ratios by the conventional wet impregnation method. The spinel layer is formed from a solution of colloidal alumina and Mg(NO₃)₂, with an apparent viscosity of around 3300 mPa s. The results indicate that a homogeneous spinel coating with excellent adherence is obtained after two immersions and a calcination at 700 °C. Both structured catalysts are active in the steam reforming of ethanol at 650 °C. The system with a Co/Ce molar ratio of 3.7 exhibits the best performance with a high stability. A complete ethanol conversion and a hydrogen selectivity of around 95% are obtained in two reaction cycles of 36 h each with intermediate regeneration.     

Hydrogen production on Pd0.01Zn0.29Mg0.7Al2O4 spinel catalyst by low temperature ethanol steam reforming reaction

This study investigated the low-temperature ethanol steam reforming (LTESR) performance of a Pd_0.01Zn_0.29Mg_0.7Al₂O₄ catalyst. Although it was present in a very small amount, the Pd component was the key to the partial CO-water gas shift and CO-methanation that, eventually, helped to increase the yield of H₂ during LTESR. An 80% yield of H₂ was maintained even after 30 h at 450 °C on the Pd_0.01Zn_0.29Mg_0.7Al₂O₄ catalyst with 100% ethanol conversion. Furthermore, the spinel structure of the catalyst remained unchanged after the reaction, and there was no increase in size owing to particle-to-particle aggregation. This study demonstrated that the Pd and Zn components could be stably located in the spinel structure of the MgAl₂O₄ with no sintering of the particles. Moreover, the oxygen transfer capacity of the MgAl₂O₄ spinel structure helped maintain the catalytic performance for long time periods by transferring oxygen to the reduced catalytic metal species (Zn or Pd) during the reaction, even though this induced oxygen defects in the spinel crystal. Overall, improved catalyst activity and an extended catalyst lifespan were observed.     

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.     

Novel highly dispersed Ni-based oxides catalysts for ethanol steam reforming

To prepare high-performance Ethanol Steam Reforming (ESR) catalyst, copper and magnesium were added into NiAl Layered Double Hydroxides (NiAl-LDHs) employing the coprecipitation method as the second and third metals for reducing the sintering of nickel active components and controlling the acid sites. Afterward, NiCuMgAl-LDHs were wrapped on the SiO₂ nanospheres to form a spherical layered structure. The results showed that, compared with the NiAl catalyst, after adding Cu metal, resulting from the synergistic effect of Ni–Cu, the ethanol conversion rate increased at different temperature ranges, and ethanol could be wholly converted at 500 °C. With the addition of Mg for neutralize the acid sites of the catalyst, no ethylene, ethanol dehydration product, was produced over the entire reaction temperature range (350–600 °C). NiCuMgAl-LDHs grows vertically on the surface of SiO₂ because its hierarchical layered structure is beneficial to inhibit the collapse of laminates, which makes the active components of Ni on SiO₂@NiCuMgAl more dispersed and exists edge and corner sites with few coordinative unsaturated active sites, thus exposing of active components and then enhanced performance. Finally, through the catalyst composition and structure optimization, the ethanol was converted entirely, and the stable hydrogen production was realized in the 19 h test.     

Ni-hydrocalumite derived catalysts for ethanol steam reforming on hydrogen production

Hydrocalumite derived catalysts prepared by co-precipitation with non-noble metal Nickel(Ni) as main active site were tested in ethanol steam reforming, and the influences of Ni (5,10,15 wt%) content were mainly tested in this research. Meanwhile, the physicochemical properties of the prepared catalysts were analyzed through different characterizations including BET, X-ray diffraction (XRD), H₂-temperature programmed reduction (H₂-TPR) and CO₂-temperature programmed desorption (TPD). As the Ni increased, the specific surface area, crystallite size of Ni, reducibility and basicity of catalysts were changed, which further affected their activities. On this basis, the best performance in this catalytic system was presented when Ni in the catalysts was 15 wt%, the ethanol conversion and hydrogen yield could reach almost 100% and 85% at 650 °C respectively. Thus, this kind of catalyst is effective for ethanol steam reforming.     

Magnesium promoted hydrocalumite derived nickel catalysts for ethanol steam reforming

Hydrocalumite derived nickel (Ni) catalysts with different loading of magnesium (Mg) (7.5/10/15 wt%, as promoters) were for the first time prepared and tested for ethanol steam reforming (ESR) in this work. The catalytic performances of different Mg promoted catalysts were mainly evaluated in the temperature range between 550 and 700 °C as determined by thermodynamic simulation. Experimental results showed that the optimal reaction temperature was 650 °C in terms of the hydrogen yields for these ESR catalysts, especially for 15Ni7.5Mg/HCa which presented a remarkable catalytic performance. Its hydrogen yields reached 90% while ethanol was almost fully converted at 650 °C. Based on the characterization results, it's believed that 15Ni7.5Mg/HCa with a certain amount of Mg loading can get the smallest Ni⁰ crystallite sizes, better H₂ reducibility and suitable basicities on strong basic sites. The catalytic performances of ESR catalysts were mainly related to the Ni⁰ crystallite size, reducibility and basicity for the prepared hydrocalumites derived Ni catalysts, and 15Ni7.5Mg/HCa could be considered as one of the best catalysts for ESR.     

Cu,Mg and Co effect on nickel-ceria supported catalysts for ethanol steam reforming reaction

Ethanol steam reforming is a promising reaction which produces hydrogen from bio and synthetic ethanol. In this study, the nano-structured Ni-based bimetallic supported catalysts containing Cu, Co and Mg were synthesized through impregnation method and characterized by XRD, BET, SEM, TPR and TPD analysis. The prepared catalysts were tested in steam reforming of ethanol in the S/C = 6, GHSV of 20,000 mL/(g_cat h) at the temperature range of 450–600 °C. Among the xNi/CeO₂ (x = 10, 13, 15 wt%) catalyst, the sample containing 13 wt% Ni with surface area of 64 m²/g showed the best performance with 89% ethanol conversion and 71% H₂ selectivity as well as low CO selectivity of 8% at 600 °C and The addition of Cu, Mg, and Co to catalyst structure were evaluated and it was found that the nature of second metal has a strong influence on the catalyst selectivity for H₂ production. Considering to results of TPR analysis, the 13Ni–4Cu/CeO₂ catalyst showed proper reduction which caused in better activity. On the other side based on TPD analysis, the more basic property of 13Ni–4Mg/CeO₂ bimetallic catalyst provided a better condition to methane steam reforming, leading to lower CH₄ selectivity and consequently more H₂ production. The 13Ni–4Cu/CeO₂ exhibited the highest activity and lowest selectivity towards ethanol conversion and CO production about 99% and 4%, while the 13Ni–4Mg/CeO₂ catalyst possessed the highest H₂ selectivity and lowest CH₄ selectivity about 74% and 1% respectively at 600 °C. The Ni–Cu and Ni–Mg bimetallic catalysts shows good stability with time on stream.     

Hydrogen production by steam reforming of ethanol over Co/CeO2 catalysts: Effect of cobalt content

The Co/CeO₂ catalysts obtained by co-precipitation method were used in the steam reforming of ethanol (SRE). The influence of cobalt active phase content (15–29 wt%), the reaction temperature (420–600 °C) and H₂O/EtOH molar ratio (12/1 and 6/1) were examined. The physicochemical characterization revealed that the cobalt content of the catalyst influences the metal-support interaction which results in catalyst performance in SRE process. The differences between catalytic properties of the Co/CeO₂ catalysts with different metal loading in SRE process decayed at 500 °C for H₂O/EtOH = 12/1. The best performance among the tested catalysts showed the 29Co/CeO₂ catalyst with the highest cobalt content, exhibiting the highest ethanol conversion, selectivity to two most desirable products and the lowest selectivity to by-products in comparison with catalysts containing smaller amount of metal. Its catalytic properties results probably from its unique physicochemical properties, i.e this catalyst contains large amount of cobalt but the metal crystallites are relatively small. Regardless cobalt content, an increase in the water-to-ethanol molar ratio in the feed increased the concentration of hydrogen an carbon dioxide and decreased formation of carbon monoxide, acetone, aldehyde and ethylene.     

Hydrogen production from the steam reforming of bioethanol over novel supported Ca/Ni-hierarchical Beta zeolite catalysts

This paper studies the H₂ production via the steam reforming of a bioresource-derived ethanol mixture over supported Ca-modified Ni-hierarchical Beta zeolite catalysts. The results showed that the hierarchical Beta zeolite with rich pore structure could be synthesized in one step by using the new quaternary ammonium gemini cationic surfactant. The zeolite had bigger BET area and pore volume than the traditional Beta zeolite. The support plays a key role for the improve of catalytic behavior. The internal structure of the catalyst can be changed by introducing calcium and nickel ions into the synthesized zeolite at the same time through ion exchange. The interaction between active metal and the support would increase, so the dispersion of the active metal can be improved. The intermediate CO₂ was efficiently absorbed by Ca in situ, which is an exothermic reaction and also help to provide the heat for the reactor. The adsorption of СО₂ in situ transmitting the reversible reforming and water gas shift reactions to the products outside their conventional thermodynamic restrictions, which enhanced H₂ production and permits high conversion to be attained. By using the method of gradient distribution of active metal in the support, the repeated catalytic effect similar to that of a hierarchical reactor was constructed, which showed excellent catalytic effect in low and medium high temperature bioethanol reforming to hydrogen. The experimental results show that when the reaction temperature is 350 °C, the 10Ni-MBeta(DI) catalyst maintains stable catalytic efficiency for continuous hydrogen production of 50 h via ESR, high hydrogen production and good stability.     

Oxidative steam reforming of ethanol on mesoporous silica supported PtNi/CeO2 catalysts

In order to assure good catalyst stability and low carbon deposition rate, in the present work three catalysts having different CeO₂ loadings (CeO₂/SiO₂ ratio ranging between 25 and 40%) were prepared by depositing Pt and Ni over a CeO₂/SiO₂ mixed support and tested for oxidative steam reforming of ethanol. All the catalysts exhibited total ethanol conversion between 350 and 600 °C; however, the CeO₂/SiO₂ ratio strongly affected catalyst stability at 500 °C: despite the similar hydrogen yields (almost 40%), the best sample, which displayed the lowest carbon formation rate (1.2 × 10⁻⁶ g_coke/(g_cat*g_carbon,fed*h)) and stable behaviour for 135 h, was the 3wt%Pt-10wt%Ni/30CeO₂/SiO₂. The lower dimension for Ni crystallites was measured over the latter exhausts catalyst and the dependence of carbon formation rate form such parameter was identified. Anyway, the carbon selectivities measured over all the investigated samples were significantly lower than the values reported in the recent literature.     

Bioethanol/glycerol mixture steam reforming over Pt and PtNi supported on lanthana or ceria doped alumina catalysts

The catalytic activity of Pt and PtNi catalysts supported on γ-Al₂O₃ modified by La and Ce oxides was investigated in the steam reforming of ethanol/glycerol mixtures. In general, all the catalysts fully converted the glycerol at the temperatures tested. However, the conversion of ethanol depended on the reaction temperature and catalyst type. The conversion into gaseous products operating at 500 °C and 450 °C was 100% using the most active catalysts (PtNiAl6La and PtNiAl10Ce). These two bimetallic catalysts gave H₂ yields close to those predicted by thermodynamic equilibrium at these temperatures. However, when the reaction temperature was lowered to 400 °C, these catalytic systems and the PtNiAl one recorded a significant decrease in ethanol conversion and H₂ yield, which moved away from the thermodynamic equilibrium value. This deviation was due to intermediate liquid products (acetaldehyde, acrolein, etc.) not being further reformed and the formation of other gaseous ones (light alkanes and ethylene). PtNiAl10Ce catalyst presented the highest conversion into gas at 400 °C, resulting in the largest H₂ yield, followed by PtNiAl6La and PtNiAl catalysts. This order is in agreement with the Ni/Al surface atomic ratio measured by XPS technique in reduced samples. However, filamentous carbon nanotubes were detected but this carbon type maintained the active sites accessible for reactants, since TEM and TGA results showed that the density of this carbon was lower for PtNiAl₁₀Ce catalyst. Pt catalysts presented lower activity than PtNi catalysts possibly due to the formation of carbon nanotubes, which covered some metallic active sites.     

Production of hydrogen by ethanol steam reforming over catalysts from reverse microemulsion-derived nanocompounds

In the present work, hydrotalcite-like compound precursor for preparing mixed oxide catalyst was successfully synthesized by a novel method, which was a combination of the reverse microemulsion and coprecipitation methods. It was observed that the precursor obtained from the above method possessed superior characteristics for preparing mixed oxide catalyst used in ethanol steam reforming (ESR). Furthermore, for comparison, catalysts prepared from conventional coprecipitation and impregnation methods had been characterized together with the catalyst prepared from the new method. Besides ICP, BET, X-ray diffraction (XRD), temperature-programmed reduction (TPR), H₂-TPD, TG, and TEM analytic techniques, catalytic performance for ESR was also investigated. The results of XRD and TPR indicated that a solid solution phase existed in the catalysts obtained from reverse microemulsion and coprecipitation methods, while spinel phase together with solid solution were observed in the catalyst obtained from the impregnation method. The high BET surface area of the catalyst obtained from the reverse microemulsion method enhanced the dispersion and the surface area of nickel, which improved the catalyst performance. From TEM images, the aggregated Ni could be found in the catalyst obtained from the impregnation method, while the hydrotalcite-like compound precursors prepared from reverse microemulsion and coprecipitation methods produced homogeneously distributed active Ni metal species. The catalyst obtained from reverse microemulsion exhibited the best activity, stability, and least carbon deposition because of the formation of hydrotalcite-like compound precursor, uniform dispersion of active Ni metal species, and much more surface area supporting the active Ni metal sites.     

Ni and Co-based catalysts supported on ITQ-6 zeolite for hydrogen production by steam reforming of ethanol

Ni and Co catalysts supported on ITQ-6 zeolite have been synthesized and evaluated in the steam reforming of ethanol (SRE). Catalysts were also characterized by means of N₂ adsorption-desorption, XRD, H₂-TPR, and H₂-chemisorption. ITQ-6 containing Co (Co/ITQ-6) presented a higher conversion of ethanol and production of hydrogen than ITQ-6 containing Ni (Ni/ITQ-6). The lower size of the metallic cobalt particles shown in Co/ITQ-6 seems to be the major responsible of its higher catalytic performance. Regarding the reaction by-products (CO, CH₄, C₂H₄O and CO₂), Co/ITQ-6 showed the lowest selectivity at medium and high temperatures (773 and 873 K). At low reaction temperatures (673 K) the dehydrogenation reaction predominates in the Co/ITQ-6, what it is supported by the high concentration of acetaldehyde detected at this temperature. In the case of the Ni/ITQ-6 the main side reaction at 673 K seems to be the methanation reaction since large concentrations of methane are detected. Stability studies were also carried out showing lower deactivation of Co/ITQ-6 at large reaction times (24 h). Characterization of the exhausted catalysts after reaction showed the presence of coke in both catalysts. Nevertheless, Co/ITQ-6 presented the lowest coke deposition. In addition, Co/ITQ-6 exhibited the lowest metal sinterization, what could be also account for the lower deactivation exhibited by this sample. This fact could be related to the higher interaction between the cobalt metallic particles and the ITQ-6 support as the H₂-TPR studies demonstrate.     

High yield hydrogen production from low CO selectivity ethanol steam reforming over modified Ni/Y2O3 catalysts at low temperature for fuel cell application

Ethanol–water mixtures were converted directly into H₂ with 67.6% yield and >98% conversion by catalytic steam reforming at 350 °C over modified Ni/Y₂O₃ catalysts heat treated at 500 °C. XRD was used to test the structure and calculate the grain sizes of the samples with different scan rates. The initial reaction kinetics of ethanol over modified and unmodified Ni/Y₂O₃ catalysts were studied by steady state reaction and a first-order reaction with respect to ethanol was found. TPD was used to analyze mechanism of ethanol desorption over Ni/Y₂O₃ catalyst. Rapid vaporization, efficiency tube reactor and catalyst were used so that homogeneous reactions producing carbon, acetaldehyde, and carbon monoxide could be minimized. And even no CO detective measured during the first 49 h reforming test on the modified catalyst Ni/Y₂O₃. This process has great potential for low cost H₂ generation in fuel cells for small portable applications where liquid fuel storage is essential and where systems must be small, simple, and robust.     

Novel zeolite-supported rhodium catalysts for ethanol steam reforming

Renewable bioethanol is an interesting hydrogen source for fuel cells through steam reforming, but its C–C bond promotes parallel reactions, mainly coke and by-products formation. In this way, good ethanol reforming catalysts are still needed, which explains current research and development efforts around the world. Most catalysts proposed for ethanol reforming are based on oxide-supported noble metals with surface area below 100 m² g⁻¹ and reaction temperatures above 500 °C. Novel Rh and Rh–K catalysts supported on NaY zeolite with surface area above 440 m² g⁻¹ are presented in this work. Reaction temperature was fixed at 300 °C and H₂O/EtOH molar ratio and reagent flow were varied. Ethanol conversion varied from 50 to 99%, with average increase of 50% due to K promoter, and hydrogen production yield achieved 68%.