Ethanol Steam Reforming Reaction Research Articles

Ethylene glycol-modified CeO2-SiO2 support for Co catalysts applied in the ethanol steam reforming

In this work, cobalt-based catalysts supported on a CeO2-SiO2 binary oxide were synthesized. The silica was functionalized with ethylene–glycol and its effect on catalytic activity, stability and selectivity towards hydrogen in the ethanol steam reforming reaction (ESR) was evaluated. The cobalt composition in all catalysts was 15 wt% and 10 wt% CeO2. The catalytic activity was evaluated at 500 °C in a fixed-bed reactor, feeding an ethanol/water mixture with a molar ratio of 5 in the ESR.A significant improvement in the activity of the modified catalysts was observed; i.e., 100% conversion and twice the H2 yield of the un-functionalized catalysts. The materials were characterized by different techniques such as XRD, N2 adsorption/desorption, Raman spectroscopy, XPS, TPR, TEM, and TPO. These results showed that the modification of the support contributed to the reduction of the cobalt particle size and the increase of dispersion, favoring H2 production.

Si4Al2O2N6 regulating chemical states of Co catalyst for improved hydrogen production from ethanol steam reforming

Tuning the metal-support interaction is a general strategy of regulating the chemical state of catalytic active site for high-efficiency hydrogen production from ethanol steam reforming (ESR) reaction. In this work, a Co catalyst supported on the Si4Al2O2N6 solid solution of Si3N4 and Al2O3 (Co/Si4Al2O2N6) has been developed to effectively catalyze ESR reaction. Our results demonstrate that the Co/Si4Al2O2N6 catalyst exhibits remarkably improved performances as compared with the Co/Si3N4 and Co/Al2O3 catalysts. In the Co/Si4Al2O2N6-catalyzed ESR reaction, ethanol conversion of 97 % has been achieved with hydrogen yield reaching 73 %. Long-time catalytic experiment manifests the Co/Si4Al2O2N6 catalyst possesses excellent durability. X-ray photoelectron spectroscopy (XPS) studies reveal that the enhanced metal-support interaction (MSI) and charge transfer from Si4Al2O2N6 support to Co species in the Co/Si4Al2O2N6 catalyst confer lower valence state on the Co catalyst supported on Si4Al2O2N6, thus promoting the C–C bond cleavage capability, leading to high C1 product yield and boosting the hydrogen-production efficiency. The catalytic mechanism studies explored by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) reveal that the Co/Si4Al2O2N6 exhibits a remarkable preference for C1 products over the Co/Si3N4 and Co/Al2O3 catalysts at low reaction temperature, thus resulting in high hydrogen-production efficiency with excellent catalytic durability.

Investigating the effects of operating parameters on the performance of sorption-enhanced membrane reactor for ethanol steam reforming reaction using computational fluid dynamics method

In this study, the performance of a sorption-enhanced membrane reactor (SEMR) was examined using a Pd-Ag membrane during ethanol steam reforming (ESR). During this study, simultaneous ESR and CO2 adsorption concept was adopted and computational fluids dynamic (CFD) method (two-dimensional model) was developed to evaluate the SEMR performance during ESR reaction. The employed CFD model for the present study provided information about the molar fractions and pressures of components to analyze driving forces under unsteady state condition. Regarding validation, the experimental data related to the membrane reactor (MR) during ESR reaction showed good agreement with modeling outcomes and the application of adsorption reaction improved MR performance. The SEMR performance was investigated after model validation, and during this step, SEMR and MR were compared. Moreover, the effects of main operating parameters, such as gas hour space velocity (GHSV), reaction pressure, and temperature, were studied to compare the SEMR and MR performance during C2H5OH conversion and hydrogen recovery. CFD modeling results showed that SEMR had better performance and increased the ethanol conversion about 20% (SEMR: 70% and MR: 59%) by temperature enhancement at low pressures compared with the conventional membrane reactor. The relative error between numerical and experimental data obtained was 3% in this study.

Renewable Hydrogen Production with Steam Reforming of Ethanol Using Siliceous Mesocellular Foam‐Supported Nickel Catalysts

Nickel (Ni) catalysts loaded on siliceous mesocellular foam (MCF‐S) are synthesized via the wet impregnation method with 3, 5, 10, and 15 wt% NiO loadings and different aging levels (no, partial, and full ageing) to determine how both factors affect the progress of the ethanol steam reforming (ESR) reaction. After extensive material characterization testing to determine material porosity, crystallinity, and Ni metal particle size and spatial location, as well as reaction testing at 300–700 °C and 4 H2O: 1 EtOH molar ratio, the fully aged 10 wt% Ni/MCF‐S possesses the strongest structural stability and catalytic activity, reaching 100% EtOH conversion and 68% H2 selectivity at 700 °C. The aging disperses and embeds more Ni nanoparticles within the walls of the mesopores, which promote the ESR reaction from easier diffusion and more active site contact within the pores. Furthermore, the catalyst reveals little signs of deactivation, as the structure remains virtually unchanged, and any coke formed is on the silica support and not over the Ni nanoparticles after the ESR reaction. Such results have demonstrated a proven applicability for ESR and a further need to research about aging effects toward improving structural properties and the catalytic reaction activity.

Effect of Potassium Doping on the Structural and Catalytic Properties of Co/MnOx Catalyst in the Steam Reforming of Ethanol.

The promotional effect of potassium (~1.25 wt%) on a Co/MnOx catalyst was studied for samples prepared by the impregnation method in the steam reforming of ethanol (SRE) process at 420 °C for a H2O/EtOH molar ratio of 12/1. The catalysts were characterized using physicochemical methods to study their textural, structural, and redox properties. The XRD studies revealed that, during the treatment of both cobalt-based catalysts under a hydrogen atmosphere at 500 °C, Co0 and MnO phases were formed by the reduction in Co3O4 and Mn2O3/Mn3O4 phases, respectively. Potassium doping significantly improved stability and ability for the C-C bond cleavage of the Co/MnOx catalyst. The enhancement of activity (at ~25%) and selectivity to hydrogen (at ca. 10%) and the C1 product, mainly carbon dioxide (at ~20%), of the Co/MnOx catalyst upon potassium doping was clarified by the alkali promoter's impact on the reducibility of the cobalt and manganese oxides. The microscopic observations revealed that fibrous carbon deposits are present on the surface of Co/MnOx and KCo/MnOx catalysts after the SRE reaction and their formation is the main reason these catalysts deactivate under SRE conditions. However, carbon accumulation on the surface of the potassium-promoted catalyst was ca. 12% lower after 18 h of SRE reaction compared to the unpromoted sample.

A strong bimetal-support interaction in ethanol steam reforming

The metal-support interaction (MSI) in heterogeneous catalysts plays a crucial role in reforming reaction to produce renewable hydrogen, but conventional objects are limited to single metal and support. Herein, we report a type of RhNi/TiO2 catalysts with tunable RhNi-TiO2 strong bimetal-support interaction (SBMSI) derived from structure topological transformation of RhNiTi-layered double hydroxides (RhNiTi-LDHs) precursors. The resulting 0.5RhNi/TiO2 catalyst (with 0.5 wt.% Rh) exhibits extraordinary catalytic performance toward ethanol steam reforming (ESR) reaction with a H2 yield of 61.7%, a H2 production rate of 12.2 L h−1 gcat−1 and a high operational stability (300 h), which is preponderant to the state-of-the-art catalysts. By virtue of synergistic catalysis of multifunctional interface structure (Rh-Niδ−-Ov-Ti3+; Ov denotes oxygen vacancy), the generation of formate intermediate (the rate-determining step in ESR reaction) from steam reforming of CO and CHx is significantly promoted on 0.5RhNi/TiO2 catalyst, accounting for its ultra-high H2 production.

Study of the impregnation sequence of active phase and effect of cobalt content over Co-CeO2/MgΑl2O4 catalysts in ethanol steam reforming

Co–CeO2/MgAl2O4 catalysts were obtained by varying the impregnation order (sequential or co‒impregnation) of active phase (Co) and Ce and were evaluated in the ethanol steam reforming (ESR) reaction. Results from TPR and XPS revealed that the impregnation order influenced the metal‒metal and/or metal‒support interactions and Co0/Con+, Ce3+/Ce4+ and the Co/Ce surface molar ratio, affecting the catalyst behavior in the ESR reaction. The solids prepared by sequential impregnation, Co/Ce/S and Ce/Co/S exhibited a greater degree of reduction than the solid obtained by co‒impregnation (CoCe/S), though these systems displayed low dispersion of Co species and low content of surface Co°. The solid CoCe/S showed the highest dispersion (68.5%) and greater presence of Co0 on the surface. The effect of the cobalt content (4, 8 and 12 wt%) was also examined in catalysts prepared using the co‒impregnation method. With the increase in cobalt content, a greater loss of stability and a greater amount of carbon deposits were observed. The highest H2 yield (5.3 mol H2/mol C2H5OH) and stability were achieved over the solid obtained by co‒impregnation with 8 wt% Co, which was attributed to the high dispersion of the active phase and its high content of surface metallic cobalt.

Operando DRIFT-MS for studying the oxidative steam reforming of ethanol (OSRE) reaction

An operando DRIFT-MS system (Diffuse Reflectance Infrared Fourier Transform Spectroscopy coupled with Mass Spectrometry) was designed and set up to study the oxidative steam reforming of ethanol reaction (OSRE). This reaction involves the mixture of water, ethanol and oxygen to produce mainly hydrogen, which is a rather attractive energy carrier. Spectroscopic monitoring of the process is a key tool to contribute to the understanding of: i) the dynamics on the catalyst surface, ii) the reaction mechanism and iii) the effect of the solid's properties on the catalytic process. In this sense, this document sets forth the experimental design that allows to carry out the study under operando DRIFT-MS conditions through time for the OSRE reaction. Selection criteria for parameters, materials, configuration, and experimental conditions are included, particularly optimizing the parameters of particle size and the dilution factor with KBr as well as the temperature and flow conditions for carrying out the reaction.•Clear signals of the adsorbed species in IR that do not present interference by water in the reaction atmosphere.•Simple assembly and online product detection by MS that allow to follow the change in the products of the OSRE reaction according to the temperature.•Controlled entry of gases and quantification by loop injection.

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.

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.

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.

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.

Magnesium addition to Ni spinels and a composite as design strategy of catalysts for ethanol steam reforming

Two synthesis strategies were considered, by one side, spinel structures were studied as precursors of Ni based catalysts and by the other side a mixed oxide composite as support in order to achieve the necessary basic characteristics that could minimize carbon formation in ethanol steam reforming reaction (ESR). For this purpose, two spinels families, Ni1-xMgxAl2O4 and Mg1-xNixAl2O4 and a composite Ni/MgO–Al2O3 were successfully synthetized. Catalysts were characterized by XRD, SBET, TPR, XPS, CO2-TPD and evaluated in ESR. The best catalytic activity was observed for Ni0.99Mg0.01Al2O4 and Ni/MgO–Al2O3. These catalysts presented the highest values of H2 selectivity and the least values of CO selectivity with almost zero formation of methane. This excellent behavior was attributed to the higher reducibility and higher amount of available Ni° species at surface with a higher support interaction. Long term experiences were conducted in order to evaluate stability. Both catalysts remained stable with minimum carbon formation.

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.

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.

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.

Improving the coking resistance of Ni/Al2O3 modified by promoter (Ce, Zr, or Mg) under ethanol steam reforming: Perspective from growth sites of coking

A series of nickel catalysts supported on Al2O3 that modified with Ce-, Zr-, and Mg-promoter were prepared via a sol-gel method and a subsequent impregnation method for the ethanol steam reforming reaction (ESR). The effect of promoters on the carbon deposition was focused. Compared with Ni/Al2O3 catalyst, the introduction of different promoters decreased the selectivity for CH2CH2 to different extent, especially, Ce-, Mg- containing catalysts completely suppressed the production of CH2CH2 for 30 h tested at 500 °C. And the medium and strong acid sites were confirmed as the major sites for CH2CH2 production. Encapsulation carbon derived from ethylene takes the primary responsibility for carbon deposition, and the formation of metal carbide is the other reason for causing carbon deposition. Among the tested catalysts, Ni/Mg–Al2O3 exhibited a better performance for anti-carbon, which was attributed to the blockage of medium and strong acid sites as well as the high Ni crystallinity.

Electrodeposition of a Li-Al Layered Double Hydroxide (LDH) on a Ball-like Aluminum Lathe Waste Strips in Structured Catalytic Applications: Preparation and Characterization of Ni-Based LDH Catalysts for Hydrogen Evolution

A functionally structured catalyst was explored for ethanol steam reforming (ESR) to generate H2. Aluminum lathe waste strips were employed as the structured catalytic framework. The mixed metal oxide (Li-Al-O) was formed on the surface of Al lathe waste strips through calcination of the Li-Al-CO3 layered double hydroxide (LDH), working as the support for the formation of Ni catalyst nanoparticles. NaOH and NaHCO3 titration solutions were, respectively, used for adjusting the pH of the NiCl2 aqueous solutions at 50 °C when developing the precursors of the Ni-based catalysts forming in-situ on the Li-Al-O oxide support. The Ni precursor on the Al structured framework was reduced in a H2 atmosphere at 500 °C for 3 h, changing the hydroxide precursor into Ni nanoparticles. The titration agent (NaOH or NaHCO3) effectively affected the physical and chemical characterizations of the catalyst obtained by the different titrations. The ESR reaction catalyzed by the structured catalysts at a relatively low temperature of 500 °C was studied. The catalyst using NaHCO3 titration presented good stability for generating H2 during ESR, achieving a high rate of H2 volume of about 122.9 L/(gcat·h). It also had a relatively low acidity on the surface of the Li-Al-O oxide support, leading to low activity for the dehydration of ethanol and high activity to H2 yield. The interactions of catalysts between the Ni precursors and the Li-Al-O oxide supports were discussed in the processes of the H2 reduction and the ESR reaction. Mechanisms of carbon formation during the ESR were proposed by the catalysts using NaOH and NaHCO3 titration agents.

β-Si4Al2O2N6 supported Ni catalyst for enhanced ethanol steam reforming: Tuning metal-support interaction by high-temperature solution of Si3N4 with Al2O3

Developing a high-performance Ni-based catalyst for ethanol steam reforming (ESR) reaction is desirable for sustainable hydrogen production. In this work, β-Si4Al2O2N6, the high-temperature solid solution of Si3N4 and Al2O3, was utilized as support to fabricate Ni catalyst (Ni/Si4Al2O2N6) for ESR reaction to enhance hydrogen-production efficiency. The catalytic experiments demonstrated that Ni/Si4Al2O2N6 catalyst exhibited higher C–C bond cleavage capacity, hydrogen-production efficiency, catalytic durability and better anti-coke performance as compared with Ni/Si3N4 and Ni/Al2O3 catalysts. H2-TPR, XPS and NH3-TPD studies revealed that the stronger metal-support interaction (MSI) in Ni/Si4Al2O2N6 catalysts induced more distinct charge transfer from Ni species to Si4Al2O2N6 support, fabricating Ni active sites with higher oxidation state and achieving higher catalytic activity and durability for ESR reaction.