Insights into the Reaction Routes for H2 Formation in the Ethanol Steam Reforming on a Catalyst Derived from NiAl2O4 Spinel
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ABSTRACT:
SUBMITTER: Valecillos J
PROVIDER: S-EPMC8573826 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:Methane steam reforming (MSR) plays a key role in the production of syngas and hydrogen from natural gas. The increasing interest in the use of hydrogen for fuel cell applications demands development of catalysts with high activity at reduced operating temperatures. Ni-based catalysts are promising systems because of their high activity and low cost, but coke formation generally poses a severe problem. Studies of ambient-pressure X-ray photoelectron spectroscopy (AP-XPS) indicate that CH4/H2O gas mixtures react with Ni/CeO2(111) surfaces to form OH, CH x , and CH x O at 300 K. All of these species are easy to form and desorb at temperatures below 700 K when the rate of the MSR process is accelerated. Density functional theory (DFT) modeling of the reaction over ceria-supported small Ni nanoparticles predicts relatively low activation barriers between 0.3 and 0.7 eV for complete dehydrogenation of methane to carbon and the barrierless activation of water at interfacial Ni sites. Hydroxyls resulting from water activation allow for CO formation via a COH intermediate with a barrier of about 0.9 eV, which is much lower than that through a pathway involving lattice oxygen from ceria. Neither methane nor water activation is a rate-determining step, and the OH-assisted CO formation through the COH intermediate constitutes a low-barrier pathway that prevents carbon accumulation. The interactions between Ni and the ceria support and the low metal loading are crucial for the reaction to proceed in a coke-free and efficient way. These results pave the way for further advances in the design of stable and highly active Ni-based catalysts for hydrogen production.
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Project description:The production of biobutanol from bioethanol by the Guerbet reaction is an alternative pathway to renewable sources. The commercial viability of this green route requires improvements in the process development. This study experimentally examines the influence of operating conditions on the performance of a Mg-Al spinel catalyst prepared from hydrotalcite precursors. This catalyst demonstrates an exceptional performance in the Guerbet reaction with a promising activity/butanol selectivity balance, excellent long-term stability, and very-low-carbon footprint (CO2 generation as by-products is minimal). This study showcases a systematic strategy to optimize the reaction parameters in the Guerbet reaction for biobutanol production using an advanced spinel catalyst. Upon carefully adjusting temperature, pressure, space velocity, and reactants co-feeding, very promising conversion (35%) and butanol selectivity values (48%) were obtained.
| S-EPMC9329697 | biostudies-literature
Project description:A series of Cu catalysts supported on SiO2, Al2O3-SiO2, TiO2 rutile, and Cu/TiO2 anatase metal oxides has been studied for methanol reforming in the vapor phase. The highest activity was obtained on Cu/SiO2 catalysts (5493 ?mol H2 min-1·gcat -1) followed by Cu/TiO2 rutile, Cu/Al2O3-SiO2, and anatase. XRD and HRTEM characterization after reaction revealed that on Cu/SiO2 significant sintering occurred during reaction. In contrast, the particle size growth on Cu/TiO2 rutile and anatase was less pronounced, which could be associated with the interaction between Cu clusters and TiO2. Characterization by TGA showed that on Cu/Al2O3-SiO2 the main cause of deactivation was coke deposition.
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Project description:The suppression of methane and coke formation over Ni-based catalysts for low temperature ethanol steam reforming remains challenging. This paper describes the structural evolution of Fe-modified Ni/MgAl2O4 catalysts and the influence of iron species on methane and coke suppression for low temperature ethanol steam reforming. Ni-Fe alloy catalysts are gradually oxidized by water to generate Ni-rich alloy and γ-Fe2O3 species at steam-to-carbon ratio of 4. The electron transfer from iron to nickel within Ni-Fe alloy weakens the CO adsorption and effectively alleviates the CO/CO2 methanation. The oxidation capacity of γ-Fe2O3 species promotes the transformation of ethoxy to acetate groups to avoid methane formation and the elimination of carbon deposits for anticoking. Ni10Fe10/MgAl2O4 shows a superior performance with a highest H2 yield of 4.6 mol/mol ethanol at 400 °C for 15 h. This research could potentially provide instructions for the design of Ni-based catalysts for low-temperature ethanol steam reforming.
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Project description:Fe-modified Cu catalysts with CeO2 support, prepared by the impregnation method, were subjected to physicochemical analysis and catalytic tests in the steam reforming of methanol (SRM). Physicochemical studies of the catalysts were carried out using the XRF, TEM, STEM-EDS, XRD, TPR and nitrogen adsorption/desorption methods. XRD, TEM studies and catalytic tests of the catalysts were carried out at two reduction temperatures, 260 °C and 400 °C, to determine the relationship between the form and oxidation state of the active phase of the catalysts and the catalytic properties of these systems in the SRM. Additionally, the catalysts after the reaction were analysed for the changes in the structure and morphology using TEM methods. The presented results show that the composition of the catalysts, morphology, structure, form and oxidation state of the Cu and Fe active metals in the catalysts and the reaction temperature significantly impact their activity, selectivity and stability in the SRM process. The gradual deactivation of the studied catalysts under SRM conditions could result from the forming of carbon deposits and/or the gradual oxidation of the copper and iron phases under the reaction conditions.
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Project description:Ni-based catalysts
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Project description:Syngas is an important intermediate in the chemical process industry. It is used for the production of hydrocarbons, acetic acid, oxo-alcohols, and other chemicals. Depending on the target product and stoichiometry of the reaction, an optimum (molar) ratio between hydrogen and carbon monoxide (H2:CO) in the syngas is required. Different technologies are available to control the H2:CO molar ratio in the syngas. The combination of steam reforming of methane (SRM) and the water-gas shift (WGS) reaction is the most established approach for syngas production. In this work, to adjust the H2:CO ratio, we have considered formic acid (FA) as a source for both hydrogen and carbon monoxide. Using thermochemical equilibrium calculations, we show that the syngas composition can be controlled by cofeeding formic acid into the SRM process. The H2:CO molar ratio can be adjusted to a value between one and three by adjusting the concentration of FA in the reaction feed. At steam reforming conditions, typically above 900 K, FA can decompose to water and carbon monoxide and/or to hydrogen and carbon dioxide. Our results show that cofeeding FA into the SRM process can adjust the H2:CO molar ratio in a single step. This can potentially be an alternative to the WGS process.
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Project description:The sorption-enhanced steam reforming of ethanol (SESRE) has recently been reported as a novel process for hydrogen (H2) production. SESRE can operate well on a Ni-based catalyst with dolomite as a sorbent in packed-bed reactors. In this study, the circulating fluidized bed (CFB) concept was proposed to obtain higher productivity and continuous operation of SESRE. Particular focus was directed to the design and selection of suitable operating conditions of the CFB riser. Two-dimensional transient models using the Euler-Euler approach and the kinetic theory of granular flows were applied to investigate the H2 production performance from a pilot-scale riser. The 2 k full factorial design method was utilized to examine the significances of five specific parameters, namely, the riser diameter, inlet temperature, catalyst-to-sorbent ratio, solid flux, and inlet gas velocity on two response variables, namely, H2 purity and H2 flux. From the ANOVA results, either the main effect or the interactions of each parameter were shown to be significant on both the H2 purity and the H2 flux, particularly the riser diameter and the solid flux. For optimizing the operation and reaction parameters, the best case was the system with riser diameter of 0.2 m, inlet temperature of 600 °C, catalyst-to-sorbent ratio of 2.54 kg kg-1, solid flux of 200 kg m-2 s-1, and gas velocity of 3 m s-1, obtaining H2 purity of 91.30% on a dry basis with a significantly high H2 flux of 0.147 kg m-2 s-1. The hydrodynamics showed that SESRE reached breakthrough within the bottom dense zone. However, incomplete conversion occurred in the core of the riser because of the very dilute bed.
| S-EPMC9082030 | biostudies-literature
Project description:In the present study, Ni/Ce-Sm-xCu (x = 5, 7, 10 at.%) catalysts were prepared using microwave radiation coupled with sol-gel and followed by wetness impregnation method for the Ni incorporation. Highly dispersed nanocrystallites of CuO and NiO on the Ce-Sm-Cu support were found. Increase of Cu content seems to facilitate the reducibility of the catalyst according to the H₂ temperature-programmed reduction (H₂-TPR). All the catalysts had a variety of weak, medium and strong acid/basic sites that regulate the reaction products. All the catalysts had very high XC3H8O3 for the entire temperature (400⁻750 °C) range; from ≈84% at 400 °C to ≈94% at 750 °C. Ni/Ce-Sm-10Cu catalyst showed the lowest XC3H8O3-gas implying the Cu content has a detrimental effect on performance, especially between 450⁻650 °C. In terms of H₂ selectivity (SH2) and H₂ yield (YH2), both appeared to vary in the following order: Ni/Ce-Sm-10Cu > Ni/Ce-Sm-7Cu > Ni/Ce-Sm-5Cu, demonstrating the high impact of Cu content. Following stability tests, all the catalysts accumulated high amounts of carbon, following the order Ni/Ce-Sm-5Cu < Ni/Ce-Sm-7Cu < Ni/Ce-Sm-10Cu (52, 65 and 79 wt.%, respectively) based on the thermogravimetric analysis (TGA) studies. Raman studies showed that the incorporation of Cu in the support matrix controls the extent of carbon graphitization deposited during the reaction at hand.
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Project description:Electrochemical partial reforming of organics provides an alternative strategy to produce valuable organic compounds while generating H2 under mild conditions. In this work, highly selective electrochemical reforming of ethanol into ethyl acetate is successfully achieved by using ultrathin Co3O4 nanosheets with exposed (111) facets as an anode catalyst. Those nanosheets were synthesized by a one-pot, templateless hydrothermal method with the use of ammonia. NH3 was demonstrated critical to the overall formation of ultrathin Co3O4 nanosheets. With abundant active sites on Co3O4 (111), the as-synthesized ultrathin Co3O4 nanosheets exhibited enhanced electrocatalytic activities toward water and ethanol oxidations in alkaline media. More importantly, over the Co3O4 nanosheets, the electrooxidation from ethanol to ethyl acetate was so selective that no other oxidation products were yielded. With such a high selectivity, an electrolyzer cell using Co3O4 nanosheets as the anode electrocatalyst and Ni-Mo nanopowders as the cathode electrocatalyst has been successfully built for ethanol reforming. The electrolyzer cell was readily driven by a 1.5 V battery to achieve the effective production of both H2 and ethyl acetate. After the bulk electrolysis, about 95% of ethanol was electrochemically reformed into ethyl acetate. This work opens up new opportunities in designing a material system for building unique devices to generate both hydrogen and high-value organics at room temperature by utilizing electric energy from renewable sources.
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