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.     

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.     

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.     

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.     

Ni/SBA-15 catalysts for hydrogen production by ethanol steam reforming: Effect of nickel precursor

The effect of nickel precursor on Ni/SBA-15 catalysts was studied in ethanol steam reforming (ESR) for hydrogen production. These catalysts were prepared via incipient-wetness impregnation method using nickel nitrate and nickel citrate precursors, respectively (denoted as Ni/SBA-15(N) and Ni/SBA-15(C), respectively), and characterized by various techniques including H₂-TPR, XRD, TEM and TG. It was found that the use of nickel citrate precursor, compared to nickel nitrate precursor, could greatly strengthen the NiO-support interaction and promote the homogeneous distribution of nickel species, to obtain the small nickel particles with high dispersion. After a 25 h time-on-stream test, much lower coke deposition was formed over Ni/SBA-15(C) than Ni/SBA-15(N). Moreover, NiC_x species had be found over the used Ni/SBA-15(C), in which the carbon could be removed easily at lower temperature to exposure the active Ni sites; While carbon nanofibers with regular graphite-structure were the primary coke species over the spent Ni/SBA-15(N), which was difficultly remove and thus covered the active Ni sites easily. Due to these, Ni/SBA-15(C) displayed the higher catalytic activities and better stabilities in ESR than Ni/SBA-15(N). In summary, nickel citrate is an excellent precursor for the preparation of Ni/SBA-15 catalysts with high dispersion and strong interaction.     

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.     

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.     

Microkinetic modelling and reaction pathway analysis of the steam reforming of ethanol over Ni/SiO2

Hydrogen production via the steam reforming of biomass-derived ethanol is a promising environmental alternative to the use of fossil fuels and a means of clean power generation. A microkinetic modelling study of ethanol steam reforming (ESR) on Nickel is presented for the first time and validated with minimal parameter fitting against experimental data collected over a Ni/SiO₂ catalyst. The thermodynamically consistent model utilises Transition State Theory and the UBI-QEP method for the determination of kinetic parameters and is able to describe correctly experimental trends across a wide range of conditions. The kinetically controlling reaction steps are predicted to occur in the dehydrogenation pathway of ethanol, with the latter found to proceed primarily via the formation of 1-hydroxyethyl. C-C bond cleavage is predicted to take place at the ketene intermediate leading to the formation of CH₂ and CO surface species. The latter intermediates proceed to react according to methane steam reforming and water-gas shift pathways that are enhanced by the presence of water derived OH species. The experimentally observed negative reaction order for water is explained by the model predictions via surface saturation effects of adsorbed water species. The model results highlight a possible distinction between ethanol decomposition pathways as predicted by DFT calculations on Ni close-packed surfaces and ethanol steam reforming pathways at the broad range of experimental conditions considered.     

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.     

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.     

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.     

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.     

Modification strategies for enhancing anti-coking of Ni-, Co-based catalysts during ethanol steam reforming: A review

Producing hydrogen from ethanol steam reforming (ESR) is a carbon-neutral and environment-friendly method, which has been expected to gradually reduce excessive emission of environmental pollution and over-exploitation of fossil resources. Low-cost nickel (Ni) and cobalt (Co) are considered the most promising active metals for industrial ESR catalysts, with the challenge that carbon deposition on such catalysts causes active site loss which limits their application. In this review, comprehensive knowledge on the ESR reaction mechanism and carbon deposition process were summarized. Based on understanding of the reaction mechanism, an anti-coking strategy keeping a balance between C–C bond scission and oxidation of hydrocarbon species was proposed. Two aspects of this strategy, including (i) enhanced C–C bond scission capability of metal, (ii) promoting effects of support for protecting the activity of metal particles and removing surface carbon, were particularly described. The revelation between the intermediate reaction and modification strategy enables the successful design of new and stable catalysts for improving anti-coking ability. This review not only shed light to the development of high-performance industrial ESR catalysts, but also contribute an innovative perspective to understand anti-coking mechanism for steam reforming of CH₃CHO, CH₃COOH, CH₃COCH₃, and even crude bio-oil.     

Ni-encapsulated graphene chainmail catalyst for ethanol steam reforming

Nickel nanoparticles encapsulated with multilayered graphene were fabricated through segregation of the dissolved carbon atoms from nickel. The catalyst, vividly described as “chainmail catalyst”, was demonstrated to be promising for ethanol steam reforming (ESR) to produce H₂. Chainmail catalysts with different content of Ni were denoted as Ni@G₂, Ni@G₄, Ni@G₈ and Ni@G₁₂, respectively. Fresh and spent catalysts were characterized to analyze the role of graphene shell using various techniques (e.g., XRD, Raman, TEM). The graphene shell can protect the Ni core away from sintering, oxidation, or corrosion. ESR was investigated with a focus on the characterization of the catalysts, reaction conditions, and reaction mechanism. The ESR tests showed that the Ni@G₄ exhibited better activity, stability and lower byproducts with no deactivation phenomena for 4 h. During ESR, ethanol was preferentially adsorbed on the external surface of the chainmail catalyst by forming p–π conjugated system. The spent catalyst could be separated easily by an external magnetic field due to the ferromagnetism of nickel core.     

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.     

Modelling of the ethanol steam reforming over Rh-Pd/CeO2 catalytic wall reactors

Existing literature data have been used to model the steam reforming of ethanol on catalytic honeycombs coated with Rh-Pd/CeO₂, which have shown an excellent performance and robustness for the production of hydrogen under realistic conditions. In this article, a fully 3D non-isothermal model is presented, where the reactions of ethanol decomposition, water gas shift, and methane steam reforming have been modelled under different operational pressures (1–10 bar) and temperatures (500–1200 K) at a steam to carbon ratio of S/C = 3 and a space time of W/F between 2·10⁻³ and 3 kg h L_liq⁻¹. According to the modelling results, a maximum hydrogen yield of 80% is achieved at a working temperature of 1150 K and a pressure of 4 bar at S/C = 3.     

The active phase of NaCo/ZnO catalyst for ethanol steam reforming: EXAFS and in situ XANES studies

The NaCo/ZnO catalyst was prepared by a co-precipitation method and the active phase for the catalyst was studied. Extended X-ray absorption fine structure (EXAFS) studies were used to obtain structural parameters of the active phase of the catalyst. In situ X-ray absorption near edge structure (XANES) studies were also employed to better understand the phase transition of the catalyst in the course of H₂-temperature-programmed reduction followed by ethanol steam reforming. The XANES analysis confirmed that the oxidic precursor of Co₃O₄ phase was transformed to CoO followed by Co metal in the course of H₂-TPR, and the Co metal phase remained stable during the reaction. The EXAFS analysis for the fresh and spent catalyst samples revealed that the characteristic features corresponding to Co–Co distance of Co metallic phase were being developed during reaction, which demonstrated that Co phase is most likely the active phase of NaCo/ZnO catalyst for the ethanol steam reforming. The catalytic activity in ethanol steam reforming for hydrogen production over the oxidized and reduced catalyst samples was measured at 773 K and 1 atm in a fixed bed reactor using a model liquid feed containing 21 vol% ethanol in water. The prereduced NaCo/ZnO catalyst gave high ethanol conversion of 99% with product distributions of 73.0% H₂, 2.2% CO, 22.1% CO₂, and 2.7% CH₄, while the calcined oxidic one exhibited poor ethanol conversion below 44% at 773 K.     

Bimetallic catalysts performance during ethanol steam reforming: Influence of support materials

Ni–Cu catalysts supported on different materials were tested in ethanol steam reforming reaction for hydrogen production. These catalysts were evaluated at reaction temperature of 400 °C under atmospheric pressure. The reagents, with a water/ethanol molar ratio equal to 10, were fed at 70 dm³/(h g_cat) (after vaporization). Analysis of the ethanol conversion, as well as evaluation and quantification of the reaction products, indicated the catalyst 10% Ni–1% Cu/Ce_0.6Zr_0.4O₂ as the most appropriate for the ethanol steam reforming under investigated reaction conditions, among the studied catalysts. During 8 h of reaction this catalyst presented an average ethanol conversion of 43%, producing a high amount of H₂ by steam reforming and by ethanol decomposition and dehydrogenation parallel reactions. Steam reforming, among the observed reactions, was quantified by the presence of carbon dioxide. About 60% of the hydrogen was produced from ethanol steam reforming and 40% from parallel reactions.     

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.     

Reaction mechanism of naphtha steam reforming on nickel-based catalysts,and FTIR spectroscopy with CO adsorption to elucidate real active sites

To improve the understanding of the hydrocarbon steam reforming reaction mechanism and the nature of the active sites, different nickel-based catalysts have been synthesized and studied under several reaction conditions. Catalysts from hydrotalcite precursors show better activity and higher coking resistance than traditionally prepared samples. Furthermore, introducing additives (Ce, Li or Co) in the hydrotalcite structure produces no blockage of the nickel active sites. Different structural and physical–chemical properties have been analyzed by XRD, TPR, BET and elemental analysis. FTIR spectroscopy with CO adsorption reveals interesting catalyst structure–catalytic behavior relationships; oxygen release through the catalyst surface is key parameter to improve steam reforming activity and coking resistance; and, highly unsaturated Ni surface atoms located on the metal–support interphase are relevant structures to the catalysis and most active sites for the steam reforming reaction. Steam reforming reaction proposed sequence involves: 1) hydrocarbon preferably activation on active Ni surface sites and steam preferred activation on basic support surface sites, 2) oxygen spill-over from the support to the metal phase, and 3) reaction between carbon and oxygen species occurring on the metal–support interphase.