Steam Reforming Of Ethanol Research Articles

Photo‐Driven Hydrogen Production from Methanol and Water using Plasmonic Cu Nanoparticles Derived from Layered Double Hydroxides

AbstractMethanol steam reforming (MSR) is viewed as an important technology in the growth of a future hydrogen economy, with methanol serving as an easily transportable and storable liquid hydrogen carrier. However, the thermocatalytic MSR reaction is energy intensive as it requires high temperatures. Herein, a novel L‐Cu catalyst is successfully fabricated for photo‐driven MSR through reduction of CuAl layered double hydroxide (CuAl‐LDH) nanosheets. L‐Cu offers outstanding activity for the photothermal conversion of methanol and water to hydrogen (160.5 µmol gcat−1 s−1) under ultraviolet‐visible irradiation, with this rate being much higher than that achieved for L‐Cu at the same temperature in the dark. Characterization studies using X‐ray diffraction, X‐ray photoelectron spectroscopy, X‐ray absorption spectroscopy, and high‐resolution transmission electron microscopy determine that L‐Cu catalyst comprise Cu nanoparticles on an amorphous alumina support. Computational calculations reveale that Cu localized surface plasmon resonance effects promote the activation of H2O, thereby underpinning the remarkable hydrogen production rates achieved during photo‐driven MSR. This study introduces a novel photothermal strategy for hydrogen generation from methanol, demonstrating the enormous potential of photothermal catalysis in the chemical and energy sectors.

Effect of support on the performance of PtRu-based catalysts in oxidative steam reforming of ethanol to produce hydrogen.

Oxidative steam reforming of ethanol (OSRE) to produce hydrogen has been investigated over a series of supported PtRu catalysts, with different supports. Bimetallic PtRu-based catalysts were prepared by the impregnation method using H2PtCl6 and RuCl3 as precursors. Six supports (reducible oxides of ZrO2, CeO2, and Co3O4, and irreducible oxides of ZnO, Al2O3, and NiO) were chosen to fabricate bimetallic catalysts. The catalytic performance of the OSRE reaction in the series of PtRu-based samples was evaluated using a fixed-bed flow reactor under atmospheric pressure. In front reaction, the catalyst was pre-activated by reduction under 200°C for 3h. The gas hourly space velocity was adjusted at 66,000 h-1, and the optimal molar ratios of the H2O/EtOH and O2/EtOH feeds were 4.9 and 0.44, respectively. The results indicated that the PtRu supported on the ZrO2 and CeO2 exhibited superior catalytic performance in the OSRE reaction under a low temperature (a TR of approximately 320°C) for producing the main products of H2 and CO2 with lower CO and CH4 by-products. Also, it was quite stable during a long time evaluation; the maximum YH2 maintained at 4.5-4.2, and the CO distribution approached 3.3-3.5mol% around 84h test at 340°C over the PtRu/ZrO2 catalyst.

Structure sensitivity of ethanol steam reforming over the Rh catalyst: Reaction kinetics and deactivation mechanisms

Rh catalyst exhibits high activity and selectivity of hydrogen production for ethanol steam reforming (ESR). In this work, we used density functional theory calculations and microkinetic modeling to study the structure sensitivity of ESR over the Rh catalyst, with stepped Rh(211) and terraced Rh(111) as models. The dominant reaction paths on the two surfaces were determined by pruning a complex network under different conditions. Further microkinetic analysis of the dominant reaction pathways suggested that Rh(211) shows higher activity and CO2 selectivity than Rh(111), but lower stability due to carbon deposition. High steam/ethanol ratio was found to be important to the reaction which can reduce carbon accumulation and improve CO2 selectivity. The transition state of CH3CH2OH dissociation is rate-controlling over both surfaces at high temperatures, while the removal processes of C* is rate controlling on Rh(211) at low temperatures, resulting in deactivation of the step edge sites. After screening several metal dopants over Rh(211), we found that the d-band center is well correlated with carbon adsorption energy, and stability trend is consistent with experiments. Our work could provide understanding of structure sensitivity and guidelines of rational Rh-based catalyst design for the ESR reaction.

Bioethanol to Hydrogen Membrane Surface Characteristics Change Study

The problem of the gradual transformation of the modern economy towards greater production and consumption of ‘green’ energy requires a significant revision of existing technologies. One of the possible ways to develop green energy is the use of hydrogen as the most environmentally friendly fuel. Hydrogen can be obtained both by electrolysis, using solar energy, and using biorenewable raw materials, which can be used as ethanol, biogas, peat, agricultural waste. At the same time, for regions with a low level of illumination, the production of hydrogen by electrolysis of water using electricity generated by solar panels is inaccessible, and therefore the processing of biorenewable raw materials can take a leading position. Bioethanol is a large-capacity product with a proven production technology that widely uses waste from agriculture and wood processing. Ethanol can be used as a feedstock for hydrogen generation by means of catalytic pyrolysis or catalytic steam reforming. Membrane-catalytic steam reforming of ethanol with the production of hydrogen makes it possible to obtain hydrogen without the use of an additional purification step, however, the efficiency and stability of the membrane becomes the determining parameter that ensures the efficiency of the entire process. The degradation of inorganic membranes during catalytic steam reforming is closely related to the change in porosity as a result of hydrolysis of the membrane surface. In this connection, the study of the physicochemical properties of membranes during operation can make a significant contribution to the development of stable catalytic membranes for hydrogen production. The article presents the results of studying the physicochemical properties of an inorganic membrane for ethanol steam reforming by the method of low-temperature nitrogen adsorption. The Langmuir, Brunauer-Emmett-Taylor, t-plot and Barrett-Joyner-Halenda models were used to estimate the surface change. An increase in the surface area of mesopores during the operation of the membrane was determined.

Concentrated Platinum‐Gallium Nanoalloy for Hydrogen Production from the Catalytic Steam Reforming of Ethanol

AbstractThe steam reforming of ethanol (SRE) is a key process for the production of H2 and other vital hydrocarbons. The present work describes the synthesis of Platinum‐Gallium (Pt−Ga) nanoalloys supported on mesostructured cellular foam (MCF‐17) via ultrasound‐assisted impregnation method. Ga was substituted with Pt in different wt.% i. e. Pt/MCF‐17, Pt99.9Ga0.1/MCF‐17, Pt99Ga1/MCF‐17, and Pt90Ga10/MCF‐17 and was evaluated towards the SRE at a temperature range of 473K‐773 K towards hydrogen (H2), acetaldehyde (CH3CHO), diethylether (DEE), ethylene (C2H4), carbon monoxide (CO), carbon dioxide (CO2), methane (CH4), and ethane (C2H6). The SRE activity and H2 formation rate with Pt90Ga10/MCF‐17 catalyst were observed to be 68.1 % and 3047.2 nmole g−1 sec−1, which is 9.8 and 4.5 times more than the Pt/MCF‐17 counterparts. Moreover, as observed from DRIFTS, NH3‐TPD and XPS studies Ga showed high interaction with Pt in the electron deficit state which resulted in the increased dehydrogenating and acidic properties that resulted in a higher yield of H2.

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.

Multi-size distributed Ni catalyst embedded in SiCxOy film by inverse microemulsion-precipitation method for ethanol steam reforming

Ni/SiCxOy catalysts with multi-size distribution of Ni particles, were prepared and supported on porous SiC ceramics by a combination of inverse microemulsion and precipitation methods, as reaction microchannels for ethanol steam reforming (ESR). The microstructure, phase composition, reduction performance, hydrogen production performance of ESR, and the type and growth of carbon deposition were investigated for Ni/SiCxOy catalysts. The Ni catalysts embedded in SiCxOy film with the appropriate amount of precipitant exhibited multi-size distribution and minimal particle size. The initial ethanol conversion rate and H2 selectivity of Ni/SiCxOy catalysts during ESR reaction were 100% and 75%, respectively, remaining 95% and 69.2% after 20 h, respectively. Raman and SEM results indicate that Ni/SiCxOy catalysts with appropriate amounts of precipitant tended to grow more loosely arranged carbon nanowires. The combination of inverse microemulsion and precipitation methods produced smaller and multi-size distributed Ni/SiCxOy catalysts with superior durability and hydrogen production performance in ESR reaction.

Steam reforming of ethanol for hydrogen production by low-temperature steam reforming using modified Ni-Sn/CeO2 catalyst

This study focuses on the development of Ni-Sn bimetallic catalysts supported on ZrO2 modified CeO2 and their application for low temperature steam reforming of ethanol (LTSRE) at different temperature 200–400 °C. The catalyst powders are prepared by an ultrasonic-assisted solution combustion synthesis method. The ethanol conversion and selectivity of H2, CO2, CO, and CH4 has been studied with feed composition H2O:EtOH = 12: 1 mol ratio, feed flow rate 0.1 cc/min, and reaction time 20 hrs. Fresh and spent catalysts are characterized using XRD, FTIR, Raman, FESEM, XPS, and TGA-DTA. ZrO2 changes the support chemistry and enhances the activity and stability of the catalyst. At 400 °C, 100 % ethanol (EtOH) conversion, 69 % H2 selectivity with least coke deposition is observed for the catalyst with 5 wt% metal (Ni:Sn = 14:1) loading on Ce:Zr 1:2 mol ratio (NiSn5/CZ12) support.

Comparative analysis of ethanol‐steam and ‐autothermal reforming for hydrogen production using Aspen Plus

AbstractA comparative analysis of the ethanol reforming concerning steam and autothermal reformer was conducted to the evaluate parametric conditions for a hydrogen‐rich product stream. The present simulation study includes a first attempt to report the optimal parametric conditions for ethanol‐steam and ‐autothermal reformer. Various operating parameters, including temperature, pressure, steam‐to‐ethanol ratio, and oxygen‐to‐ethanol ratio, were considered in this analysis. The result illustrated that the hydrogen mole fraction increased with rising temperature in the steam reforming of ethanol, but it remained constant beyond reaction temperature of 750°C. On the other hand, as the pressure and the steam‐to‐ethanol ratio increased, the H2 mole fraction decreased. Furthermore, with an enriched oxygen‐to‐ethanol ratio reactant stream, H2 and CO contents in the product effluent were found to be reduced in the autothermal ethanol reforming. The results showed that an autothermal reforming strategy under optimized parameters (temperature of 600°C, steam‐to‐ethanol ratio of 5, and oxygen‐to‐ethanol ratio of 0.6) produced the maximum H2 yield (3.78 kmol/h) per mole of ethanol. It was observed that introducing O2 into the reformer helped reduce the amount of energy required for the steam reforming reaction. This study indicates that, although considerable work has been conducted on reforming catalysts development, simulation‐based studies are still useful to help understand the overall process behaviour without undertaking laborious, high‐cost involved time‐consuming experiments.

The mechanism of ethanol steam reforming on Co10|α-Al2O3 (0001) surface: A DFT study

ESR (Ethanol steam reforming) seems to be a promising way to produce hydrogen which has been proposed as the most desirable energy carriers to overcome the problem of fossil fuels shortage. The ESR mechanism on the optimized Co10|α-Al2O3 (0001) surface is investigated by means of DFT calculations. The results show that oxidation state of Co cluster and micro-chemical environment play important roles in the ESR reaction. C-C bond scission is favored on the Co0 site while C-O bond scission is likely to happen on the Cox+ site, and the energy barrier is influenced by the number of hydrogen and oxygen atoms that are bonded with C/O atom. ESR reaction is initiated by the O-H bond scission of ethanol on the Cox+ site: CH3CH2OH*→ CH3CH2O*→CH3*+CH2O*→CH2O*+OH*→H2COOH*→COOH*+H2*→CO*+H2*with the dehydrogenation of H2COO* as the rate-determining step.

Investigating the influence of Ni-CexZr1−XO2 interaction on oxygen vacancy and catalytic behavior of Ni/CexZr1−XO2 catalysts for ethanol steam reforming

Ni/CexZr1−xO2 catalysts were synthesized with two types of CexZr1−xO2 solid solutions to understand the role of oxygen vacancy in ethanol steam reforming (ESR). The cubic Ce0.93Zr0.07O2 (CZ) contained more oxygen vacancies on the surface and in the lattice structure than the tetragonal Ce0.07Zr0.93O2 (ZC). Even though the Ni-CexZr1−xO2 interaction basically increased the surface oxygen vacancy (OVS) on the interfacial region, it also induced different bulk oxygen vacancy (OVb) behavior: no OVb over Ni/ZC and no change over Ni/CZ. In the ESR, active oxygen species (Ox) generated on the OVS simultaneously involved SR, and water gas shift reaction (WGS) to produce H2. Zero OVb over Ni/ZC influenced the Ox involving–reaction routes, resulting in the limitation of WGS and the high TOF values at 750 °C. Furthermore, since the OVb played a significant role as the Ox carrier, Ni/CZ showed the highest H2 production rate in the ESR at 750 °C.

Hydrogen production from tar steam reforming over hydrangea-like Co-phyllosilicate catalyst derived from Co/Sepiolite

Co-phyllosilicate with structure flexibility is acknowledged as a promising catalyst for hydrogen production by steam reforming. In this work, a series of hydrangea-like Co-phyllosilicate catalysts were synthesized by a template-free urea hydrothermal method, where the silica source was supplied by amorphous sepiolite. Both the exsolution property of phyllosilicate and the hierarchical macro-/meso-pore architectures of hydrangea-like morphology were combined to improve the metal dispersion and reactant activation. The catalytic behaviors of as-synthesized xCo/SEP-PS catalysts were evaluated in simulated tar (phenol + ethanol) steam reforming. It was founded that 10Co/SEP-PS catalyst achieved an optimal conversion (89.3%) and H2 yield (67.4%) at 700 °C, as well as the lowest apparent activation energy of 35.5 kJ/mol. Various characterization results coupling with experimental investigations indicated that the fine Co particles implanted on Co-phyllosilicate lamella were highly stable and active for H2 production. Meanwhile, the hydrangea-like Co-phyllosilicate provided high Lewis acidity and developed pore structure, significantly facilitating the reactant adsorption and activation, especially for phenol dehydrogenation. The synergy between developed pore structure and enhanced metal-support interaction of Co-phyllosilicate conferred 10Co/SEP-PS with a robust durability in a 50 h stability test and effective resistance to metal sintering and coke deposition.

Numerical simulation of a combined system of ethanol steam reforming and HT-PEM fuel cell

ABSTRACT In the present study, the integrated system of ethanol steam reforming (ESR) and the high temperature polymer electrolyte membrane fuel cell (HT-PEMFC) is simulated using ASPEN Plus™ and MATLABTM, respectively, in order to develop a clean energy technology. In ESR section, an ethanol steam reforming reactor (ESRR) is simulated using the R-Plug reactor based on a mechanistic kinetic model instead of a simple R-Gibbs reactor to consider the complexity of ESR reactions and a water gas shift reactor (WGSR) using the R-Equilibrium reactor modules of ASPEN Plus™ to obtain the optimal hydrogen production conditions. The simulated results show good agreement with the experimental observations for hydrogen yield, and it is found that the yield of hydrogen increases with increase in temperature and S/E ratio with minimal effect of pressure on it. Based on ESR section simulations, the optimal operating conditions of 923 K with S/E ratio of 4 under atmospheric condition are selected for ESRR and 423 K for WGSR to maximize hydrogen yield and minimize CO amount, respectively. The ESR section product is found to produce the fuel-cell-grade hydrogen [0.25 mole % of CO (dry, CO2-free basis) with the remaining as hydrogen] to be used in the HT-PEMFC section. The performance of HT-PEMFC section combined with ESR section is analyzed using MATLABTM, for the operating parameters like temperature, pressure, and feed CO concentration.

A comparative DFT study of ethanol steam reforming over Co(1 0 0) and CoO(1 0 0) surfaces: Molecular reaction mechanism

Unraveling the roles of cobalt sites with different oxidation states is crucial for understanding mechanism of cobalt-catalyzed ethanol steam reforming (ESR) reaction. In this work, the roles of Co(0) and Co(II) sites in ESR reaction are comparatively explored by DFT calculation studies about reaction pathways over Co(100) and CoO(100) surfaces, and a novel molecular reaction mechanism has been provided. The results demonstrate that the Co(II) site in Co-based catalyst exhibits distinct preference for dehydrogenation over dehydration of ethanol especially in the presence of H2O molecule. For the conversion of acetaldehyde, the Co(0) site exhibits significant preference for decomposition and water addition over aldol addition of acetaldehyde, thus facilitating the carbon chain shortening to improve ethanol steam reforming. Therefore, the Co(0) and Co(II) sites exhibit synergistic effects on ESR reaction, especially the role of Co(0) site in selective conversion of acetaldehyde is more crucial for high-efficiency reforming of ethanol.

Steam reforming of bio-alcohols over Ni-M (Cu, Co, Pt)/MCF-S (MgO, La2O3, CeO2) for renewable and selective hydrogen production: Synergistic effect of MCF silica and basic oxides on activity and stability profiles

In the current investigation, highly active, and stable catalyst-support systems were developed by employing the benefits of the 3D mesoporous arrangement of MCF silica and O2− Lewis basic sites of MgO, La2O3, and CeO2 in a single system for renewable and selective H2 production via steam reforming (SR) of bio-alcohols, viz., ethanol (SRE), glycerol (SRG), n-butanol (SRB), and ethylene glycol (SREG). The impact of aging time [24, 48, and 72 h ] on structural and surface features of MCF silica was also investigated to develop novel type of mesoporous materials with the best textural properties, viz., Cu-Ni-Co/MCF-MgO for SRE, Ni-Cu/MCF-La2O3 for SRG, Pt-Ni-Cu/MCF-La2O3 for SRB and Ni-Cu/MCF-CeO2 for SREG which were characterized by several physio-chemical techniques; for instance, BET, H2-TPD, H2-TPR, TGA, XRD, TEM, SEM, EDX as well as high-resolution XPS analysis. The efficacy of the combination of MCF silica with basic metal oxides was evident from the results showing nearly complete reactant conversion, no coke formation, high selectivity (>84 % H2 yield), and long-term stability beyond 680 h (> 68 h time on stream (TOS) for one cycle over > 10 cycles) for all bio-alcohols whereas MCF silica without any basic metal oxides, i.e. Ni-Cu/MCF was stable only up to ≤ 64 h (≤ 16 h TOS for one cycle up to ≤ 4 cycles) due to the absence of O2− Lewis basic sites leading to coking. Such a huge difference in catalytic stability between MCF-S (MgO, La2O3, CeO2) and Ni-Cu/MCF catalysts clearly justifies the synergistic effect of the 3D mesoporous structure of MCF silica and O2− Lewis basic sites on high metal dispersion, strong metal-support interaction (SMSI), coke inhibition. It proved their efficacy as potential commercial SR catalysts for sustainable H2 production from bio-alcohols. Finally, catalytic reaction mechanisms were developed for SRE, SRG, SRB, SREG and intrinsic reaction kinetics were studied over their corresponding catalyst-support systems in the absence of external mass transfer and intra-particle diffusion resistancs. The apparent activation energies for SRE, SRG, SRB, and SREG were calculated as 7.2, 11.2, 10.5, and 12.1 kcal/mol, respectively.

DBD plasma-assisted ethanol steam reforming for green H2 production: Process optimization through response surface methodology (RSM)

This work investigates ethanol steam reforming (ESR) to produce hydrogen (H2) in a dielectric barrier discharge (DBD) plasma reactor. A five-level, three-factor experiment design was performed using a response surface methodology (RSM) to evaluate the combined effects of the three process parameters, including discharge power, total flow rate, and ethanol-to-water (EtOH/H2O) molar ratio on the plasma-assisted ESR reaction. Quadratic regression models were employed in RSM to fit the experimental results and present the correlation between process parameters and targeted responses (EtOH conversion, H2 yield, H2 selectivity, and specific energy requirement (SER) for H2 production). The results suggested that the EtOH/H2O molar ratio is considered to have the most significant effect on the EtOH conversion and H2, H2 selectivity, while the total flow rate is the most significant parameter determining SER for H2 production. Process optimization demonstrated the optimal process conditions, including a discharge power of 55.9 W, a total flow rate of 26.7 ml/min, and an EtOH/H2O molar ratio equal to 0.34. A validation test was performed and confirmed the feasibility of the optimization process.

Appraisal of Ni Species Supported on Porous MgO during Ethanol Steam Reforming by XAS

AbstractOperando time‐resolved X‐ray absorption spectroscopy (XAS) was used to determine nickel species supported on porous MgO during the ethanol steam reforming reaction. The Principal Component Analysis (PCA) of the nickel K‐edge XAS spectra revealed Ni(OH)2, NiMgO, and metallic Ni during the activation and reaction of the catalysts. The Multivariate Curve Resolution‐Alternating Least Squares (MCR‐ALS) method for the time‐resolved XAS spectra data permitted to calculate the concentration of species during the activation and reaction steps and to determine the formation of NiMgO and nickel reduction degree. The samples prepared with surfactants, Ni10MgO‐F127 and Ni10MgO‐P123, showed less nickel reduction (less than 30 %) but were more active and stable than the reference Ni10MgO catalyst, which reduced 52 %. It happened due to the smaller particle size and a larger specific area of the porous supports. The samples synthesized without Pluronic deactivated, and ethanol dehydrogenation became predominant instead of the ethanol steam reforming.

Electron density donation of concomitant peroxide anions in La0.25Ce0.75O1.88 boosting cobalt-catalyzed ethanol steam reforming for hydrogen production

Tuning the valence state and reducibility of Co active site in Co-based catalysts to improve catalytic performances is desirable for hydrogen production from ethanol steam reforming (ESR) reaction. In this work, we fabricate Co/LaxCe1−xO2−x/2 (x = 0.5, 0.25, 0.17) catalysts and investigate their catalytic performances for ESR reaction. Our studies manifest that the catalytic performances of Co-based catalysts have been effectively improved by La doping in CeO2. Among the investigated catalysts, Co/La0.25Ce0.75O1.88 exhibits the highest catalytic activity and durability, the hydrogen yield reaches as high as 80 % at ethanol conversion of 100 %, with an excellent durability during long-time (58 h) catalytic experiment. X-ray photoelectron spectroscopy (XPS) and hydrogen temperature programmed reduction (H2-TPR) studies demonstrate that the valence state and reducibility of the Co/La0.25Ce0.75O1.88 are effectively regulated via donation of electron density from the concomitant peroxide anions in La0.25Ce0.75O1.88 to the supported cobalt catalyst, the CC bond cleavage capability has been significantly enhanced to boost the hydrogen-production efficiency from ESR reaction. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) studies reveal that Co/La0.25Ce0.75O1.88 shows a remarkable preference for producing C1 products, the Co species in low valence state and with high reducibility result in highly efficient CC cleavage and excellent catalytic durability.

Bifunctional Ni–CaO catalysts modified with CeO2 and inert Ca12Al14O33 for sorption-enhanced steam reforming of ethanol

In this work, sorption-enhanced steam reforming of ethanol (SE-SRE) process was studied using Ni–CaO-based bifunctional catalysts modified with Ca12Al14O33 (mayenite) and CeO2. The CaO and CaO/Ca12Al14O33 sorbents were synthesized by a sol-gel method and, subsequently, CeO2 and Ni were added by the incipient wetness impregnation method. These materials were characterized by BET surface area, thermogravimetric analysis (TGA), in situ X-ray diffraction (XRD), and in situ X-ray absorption near edge structuare (XANES). In addition, the catalysts were tested on 10 cycles of SE-SRE reaction and regeneration. In general, the characterization results revealed an inverse relationship between average crystallite size of CaO and CO2 sorption capacity. By the in situ XRD/XANES, the addition of the mayenite reduced by half the average crystallite size of CaO and increased the interaction between support and active phase. As a consequence, the catalyst containing mayenite (NiCaAl) showed the best CO2 capture uptake and stability, which could be justified mitigation of the CaO sintering effect by the inert material presence. Great stability was also observed in the catalytic tests, since the duration of the pre-breakthrough stage for NiCaAl and for the catalyst containing maynite and ceria (NiCaAlCe) remained constant over the reaction cycles. In terms of hydrogen production, NiCaAl catalyst showed the highest H2 molar fraction during the pre- (90%) and post-breakthrough. The CeO2 addition slightly favored the methane formation, although did not bring significant benefits in the CO2 capture and catalytic performance. Therefore, NiCaAl showed the best CO2 capture capacity and stability, which led to the best SE-SRE performance.

Effect of CeO2 on carbon deposition resistance of Ni/CeO2 catalyst supported on SiC porous ceramic for ethanol steam reforming

Ni/CeO2 catalysts (nCeO2:nNi = 0, 1, 4, 7, 10) supported on SiC porous ceramics for ethanol steam reforming (ESR) were investigated with respect to hydrogen production performance and growth of carbon deposition. The oxygen released from CeO2 enables the oxidation of CHx species to serve as carbon precursors, thus providing Ni/CeO2 catalysts with stronger resistance to carbon deposition compared with Ni catalysts. The Ni/CeO2 catalysts prepared by inverse microemulsion and impregnation methods exhibit regular semicircular spherical shape on SiC porous ceramics. Under 500 °C for 25 h of ESR reaction, the ethanol conversion rate over Ni/CeO2 catalysts (nCeO2:nNi = 7) is sustained up to 100% and H2 selectivity is essentially kept at 74%. The by-product selectivity declines stepwise with increasing content of CeO2, which is attributed to the adsorption and oxidation of CO and of CHx species as CH4 precursor from CeO2. The scanning electron microscopy (SEM) and transform electron microscopy (TEM) results reveal that further loading of CeO2 on the surface of Ni catalysts can alleviate both migration and sintering of Ni particles. Furthermore, carbon deposition on Ni/CeO2 catalysts preferentially outgrow filamentous rather than amorphous carbon, with a tendency for the latter to be more deactivated.