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.     

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 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.     

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%.     

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.     

Pathways of ethanol steam reforming over ceria-supported catalysts

Ceria-supported Pt, Ir and Co catalysts are prepared herein by the deposition–precipitation method and investigated for their suitability in the steam reforming of ethanol (SRE) at a temperature range of 250–500 °C. SRE is tested in a fixed-bed reactor under an H₂O/EtOH molar ratio of 13 and 20,000 h⁻¹ GHSV. Possible pathways are proposed according to the assigned temperature window to understand the different catalysts attributed to specific reaction pathways. The Pt/CeO₂ catalyst shows the best carbon–carbon bond-breaking ability and the lowest complete ethanol conversion temperature of 300 °C. Acetone steam reforming over the Ir/CeO₂ catalyst at 400 °C promotes a hydrogen yield of up to 5.3. Lower reaction temperatures for the water–gas shift and acetone steam reforming are in evidence for the Co/CeO₂ catalyst, whereas the carbon deposition causes its deactivation at temperature over 500 °C.     

Autothermal reforming of ethanol on noble metal catalysts

Autothermal reforming of ethanol on zirconia-supported Rh and Pt mono- and bimetallic catalysts (0.5 wt-% total metal loading) was studied as a source of H₂-rich gas for fuel cells. The results were compared with those obtained on a commercial steam reforming catalyst (15 wt-% NiO/Al₂O₃). The Rh-containing catalysts exhibited the highest selectivity for H₂ production and were stable in 24 h experiments. The formation of carbonaceous deposits was lower on the noble metal catalysts than on the commercial NiO/Al₂O₃ catalyst. Thus, the Rh-containing catalysts are more suitable than the commercial NiO/Al₂O₃ catalysts for the ATR of ethanol.     

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.     

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.     

Steam reforming of ethanol with zirconia incorporated mesoporous silicate supported catalysts

Steam reforming of ethanol is a promising route for the production of high purity hydrogen. Ni impregnated zirconia, with high chemical and thermal stability and high water adsorption-dissociation capability is an attractive catalyst for this reaction. In the present study, mesoporous zirconia and high surface area zirconia/silicate structured materials, such as Zr-SBA-15 and Zr-MCM-41, were synthesized following hydrothermal routes, using different surfactants as the structure directing templates. Surface area values of Ni impregnated mesoporous Zr-SBA-15 and Zr-MCM-41 catalysts with molar Zr/Si ratios of 0.13 and 0.45 were 515 and 338 m²/g, respectively. Ethanol reforming tests performed with these catalysts, in the temperature range of 550–650 °C, proved the potential of these materials to achieve very high hydrogen yields, over 90% of the maximum yield value of 6 mol per mole of ethanol reacted. Type of support material, Ni distribution and cluster size over the catalyst, reaction temperature and steam to ethanol ratio were found to have strong influence on coke formation and stability of hydrogen yield.     

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.     

Steam reforming of ethanol over copper-zirconia based catalysts doped with Mn,Ni, Ga

The activity toward hydrogen production in steam reforming of ethanol (SRE) reaction has been evaluated for CuO/ZrO₂ catalysts doped with Mn, Ni, Ga at 350 °C. The copper based catalysts were synthesised by co-precipitation method at constant pH = 7 and fixed (wt.%) CuO/ZrO = 2.3. The catalysts were characterised by means of N₂ adsorption, temperature programmed reduction (H₂-TPR), N₂O dissociative chemisorption, X-ray diffraction (XRD), CO₂ temperature programmed desorption (CO₂-TPD), and temperature programmed oxidation (TPO). It has been found that copper based catalysts exhibit high ethanol conversion in SRE (>86%) at 350 °C. Due to basic character of catalysts, the formation of acetaldehyde is observed. The CuO/ZrO₂ catalyst modification with dopants increases the hydrogen yield with maximum (52%) for CuO/ZrO₂/NiO. The addition of Ni changes the distribution of carbon-containing products. In this case, the increase in selectivity to CO, CO₂ and CH₄ is observed whereas selectivity to acetaldehyde is significantly decreased. This shows that presence of Ni facilities the C–C bond cleavage. On the other hand, the formation of acetic acid is limited upon addition of Mn and Ga. For all modified catalysts, decrease in carbon deposition rate during SRE is pronounced according to TPO experiments. The modification of Cu/Zr with Mn, Ni and Ga causes the decrease in copper particle size, which hinders the carbon deposit formation.     

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.     

Steam reforming of ethanol over nickel-tungsten catalyst

Ni-W/Al₂O₃ catalysts were synthesized, characterized and tested for the steam reforming of ethanol from 300 to 600 °C. Addition of Ni and W on the alumina, decreased the surface area and increased the pore volume of the mesoporous materials synthesized. The reaction products obtained were: H₂, CO₂, C₂H₄, CH₄, CO₂, CO and CH₃CHO. A promoting effect of Ni-W was observed in the conversion of ethanol to H₂ from 15 to 30 wt.% Ni and 1 wt.% W. The selectivity to H₂ on the alumina with Ni-W, was between 66.53 and 68.53% at 550 °C, appearing some undesirable products, with low ratio of CO/CO₂. Reaction was studied on a fixed bed reactor at atmospheric pressure with an ethanol/water molar ratio of 1:4, from 300 to 600 °C. The catalysts were characterized by the thermal gravimetric analysis (TGA)-Differential thermal analysis (DTA), N₂ physisorption (BET and BJH methods), X-ray diffraction (XRD) and scanning electron microscopy (SEM), these techniques were used for characterization, before and after of the steam reforming.     

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.     

Excess-methane dry and oxidative reforming on Ni-containing hydrotalcite-derived catalysts for biogas upgrading into synthesis gas

The activity of Ni-containing hydrotalcite-derived catalysts was assayed in the excess-methane dry reforming of different CH₄-CO₂ mixtures, aiming to simulate biogas upgrading to hydrogen and/or syngas. These catalysts yielded methane conversions quite far away from the thermodynamically predicted values, pointing to the inhibition of important methane consuming reactions, such as direct methane decomposition (DMD). Adding oxygen to the gas mixture (12.5%) results in increased methane conversions. Almost constant H₂/CO ratios, around 1.5, were measured at any temperature (600–850 °C). However, solid carbon formation was found to take place to a higher extent. The intrinsic properties of the hydrotalcite-derived catalysts tested results in favored reverse water gas shift reaction, leading to CO₂ and H₂ conversion.     

Regenerable and durable catalyst for hydrogen production from ethanol steam reforming

In this work, perovskite-type oxides La_1−xCa_xFe_0.7Ni_0.3O₃ were prepared by using a citrate complex method. The catalysts were employed in the reactions of steam reforming of ethanol (SRE) and oxidative steam reforming of ethanol (OSRE) to produce hydrogen. A reduction-oxidation cycle was proposed to overcome the problems of active component sintering and carbon deposition encountered in SRE reaction. In the ex-situ reactions, highly dispersed surface nickel particles formed during the reduction of La_1−xCa_xFe_0.7Ni_0.3O₃, while during the introduction of an oxidative atmosphere these particles could be oxidized and restored back into the perovskite bulk. Owing to the existence of this segregation-incorporation cycle of nickel species in the perovskite oxides, the sintering of nickel particles under OSRE was found depressed effectively. Besides, this work proved that the oxygen in the feed is helpful to the elimination of deposited carbon. It seems promising for overcoming the problems of the active component sintering and carbon deposition in SRE reaction by regulating the redox ability of the perovskite-type oxides and the feed composition.     

Hydrogen production over Rh/Ce-MCM-41 catalysts via ethanol steam reforming

1 wt%Rh/Ce-MCM-41 catalysts were synthesized using Ce-MCM-41 as support where Si/Ce molar ratio varied from 10 to 30 and 50. During hydrogen reduction process, metallic Rh particles were formed on the Ce-MCM-41 at around 130 °C with an average particle size 6.8 nm. These catalysts were tested in the ethanol steam reforming (ESR) under atmospheric pressure between 225 and 425 °C. Compared to Rh/MCM-41 catalyst, cerium introduction would significantly enhance both the catalytic activity and hydrogen yield by approximately 2–3 times. However, the amount and the method of Ce incorporation in the framework of MCM-41 could greatly impact the catalytic performance of the Rh/Ce-MCM-41 catalysts. The ethanol conversion at 425 °C over the Rh/Ce-MCM-41 catalysts increased from 90.0% to 95.1% and 99.9%, as the Si/Ce molar ratio increases from 10 to 30 and 50. However, product selectivity is almost independent of the cerium content. The direct hydrothermal method of introducing Ce into the framework of MCM-41 is much superior to the impregnation route in the ESR reaction. After 6 h of reaction, the catalysts remain the mesostructure and the chemical state of cerium ions unchanged. Trace coke with graphite-like structure deposited on the surface does not modify the catalytic performance.     

Hydrogen production by oxidative ethanol reforming on Co, Ni and Cu ex-hydrotalcite catalysts

Five Co, Ni and Cu oxides derived from hydrotalcite-like precursors (ex-LDHs) were prepared and tested in the oxidative steam reforming reaction of ethanol under autothermal conditions. Highly crystalline LDH-precursors were obtained using urea hydrolysis method and both the precursors and the calcined ex-LDH oxides were characterized with several physical and chemical techniques. It has been shown that the particle size of the segregated active metal oxide decreases upon increasing the crystallinity of the LDH-precursor. Moreover, these small particle sizes favour the strong interactions between active metals and the amorphous matrix of Al-modifying cations, which cause a high stabilization of the active metal phases.All the ex-LDH catalysts (Co-Zn-Al, Co-Mg-Al, Co-Al, Ni-Mg-Al and Cu-Mg-Al) were tested in the oxidative steam reforming of ethanol with EtOH/H₂O molar ratio (nH₂O/nEtOH) of 2.28 and O₂/EtOH molar ratio (nO₂/nEtOH) of 0.36, at temperatures of 848-898-948 K. All ex-LDH catalysts, apart from Cu-catalyst, reached the full ethanol conversion in the temperature range, and H₂ and CO₂ were the main reaction products. Thus, high absolute H₂ production values of 14.5 L(STP) h⁻¹ g_cat⁻¹ at 848 K with CoZnAl ex-LDH catalyst and nearly 18 L(STP) h⁻¹ g_cat⁻¹ at 948 K with CoAl and CoMgAl catalysts were reached, which means H₂ selectivity values of 85% at 848 K and 89% at 948 K, respectively.