Steam Conversion Research Articles

Thermal Integration of Solid Oxide Electrolysis Cell Systems with External Heat Sources to Maximize Heat Recuperation and Exergetic Efficiency

Green hydrogen is expected to play a significant role as an energy carrier in the future energy system. As the issue of climate change due to greenhouse gas emissions has recently emerged, efforts are being made to change from a carbon-based energy society to a hydrogen-based energy society worldwide. Among several hydrogen production technologies, green hydrogen refers to hydrogen that does not generate carbon dioxide at all in production processes such as water electrolysis by using renewable energy. The hydrogen production through water electrolysis is more mature than other green hydrogen production technologies and is the most popular green hydrogen production method because it is easy to mass-produce with a modular structure. In particular, a solid oxide electrolysis cell (SOEC) system, which has the highest efficiency among electrolysis systems, is drawing significant attention.The high efficiency of SOEC systems originates from heat utilization for water electrolysis, which makes it critical to have optimal thermal integration. The SOEC systems operating at the high temperature above 700°C need a significant amount of thermal energy for steam generation and inlet gas heating. To deal with these thermal energy requirements, the internal heat recuperation and the external heat source integration with system components must be implemented in an effective manner. The thermal integration is the most important part of the SOEC system design. However, the majority of previous studies have concentrated on the performance of unit-cells and stacks, ignoring thermal energy consumption of the systems and heat integration.The purpose of this study is to explain the basis of thermal integration and to investigate the effects of internal and external thermal integration on the whole system performance. The basic concept of the thermal integration of SOEC system is presented while considering internal heat recuperation and coupling with external heat sources. By using temperature-heat transfer analysis, the procedure to design the optimal thermal integration of the SOEC system is described. Based on the proposed system, a parametric study with respect to stack operating conditions (i.e., stack inlet temperature, air utilization, steam conversion, hydrogen fractions) is conducted in order to elucidate their effect on the system level performance. Then, the effects of external heat sources such as steam injection, indirect heat transfer with hot fluids and heat supply by an electrical heater are examined, with pinch analysis and exergetic performance evaluation. The results show that high temperature external heat is not always a prerequisite for the SOEC system. The systematic comparison with several heat integration methods provides a clear guideline to maximize the exergetic efficiency when designing and operating SOEC systems. Through the analysis, this study provides understanding the internal and external characteristics of the thermal integration.

Modeling Delamination of Electrodes of Solid Oxide Electrolyzers with Fuel Electrode as a Support

Solid oxide electrolyzers (SOE) are the most efficient yet not fully mature devices for electrochemical production of hydrogen. These devices offer a great advantage in applications which make it possible to utilize process heat or steam to feed SOE for direct conversion of steam instead of water. However, the technology is prone to a degradation, as it combines advanced materials, requires dedicated fabrication techniques and it operates at elevated temperature, typically above 650ºC. One of the biggest challenges is the mitigation of degradation of solid oxide electrolyzers due to the delamination of the electrode. Several measures can be proposed to limit the process, however full elimination of this type of degradation is not yet possible. The good understanding of the mechanisms and consecutive steps which lead to deterioration of the interface between the electrolyte and air electrode of SOE is based on thorough experimental studies supported by the numerical modeling.In the study we present a delamination model, which can be used to identify the safe operating envelope of SOEs with a given structure and material composition. The mechanisms behind degradation through delamination are discussed with respect to the chemical and electrochemical potentials. This is complement by the discussion of criteria for the formation and propagation of cracks, taking into account the oxygen potential at the electrolyte-electrode interface. Moreover, the microstructural modifications of the electrodes, e.g. increase of its porosity, are discussed as one of the potential measures to substantially reduce the risk of delamination under design point and off-design operation of SOEs. The methodology of manipulating the porosity of the electrode by varying the content and type of pore forming agents was proposed in order to adjust the parameters of electrodes to the required microstructure. Results of the experimental characterization of cells fabricated in such a way are presented, and the guidelines for fine-tuning the microstructure are discussed with respect to the degradation mechanisms.

Reverse Water Gas Shift Versus Carbon Dioxide Electro-Reduction: The Reaction Pathway Responsible for Carbon Monoxide Production in Solid Oxide Co-Electrolysis Cells

Solid oxide co-electrolysis cells are an emerging technology that can utilize renewable energy sources for the conversion of steam and carbon dioxide into valuable chemicals and feedstocks. An important challenge in the analysis of these devices is understanding the reaction pathway(s) responsible for the production of carbon monoxide. Some researchers have suggested that it is largely attributed to the reverse water gas shift reaction, since the polarization curves of pure steam electrolysis and co-electrolysis overlap each other; therefore, they surmised the electro-reduction of carbon dioxide is inconsequential to carbon monoxide production. Conversely, other studies have shown the polarization curves corresponding to co-electrolysis lie between those of pure steam and pure carbon dioxide electrolysis, thus indicating the reverse water gas shift reaction and the electro-reduction of carbon dioxide are both contributors. For the first time, this analysis attempts to untangle the conflicting phenomena observed in previous experiments by utilizing dimensional analysis, thermodynamics, and reaction kinetics. We illustrate the operating regime in which both reaction pathways contribute to the production of carbon monoxide, while demonstrating that the reverse water gas shift reaction is inconsequential when steam electrolysis and co-electrolysis polarization curves coincide, which is contrary to what has been concluded in previous analyses. This work is intended to provide an enhanced understanding of the observed behaviour of solid oxide co-electrolysis cells, and can help designers and researchers make informed decisions on how to construct their cell to exploit a desired reaction pathway.

Degradation Behavior of MK35x Stacks with Chromium-Based Interconnects in Steam Electrolysis Operation

The currently ongoing commercialization of high-temperature solid oxide electrolysis (SOEL) requires the understanding of the underlying dominant degradation mechanisms to enable continuous progress in reducing stack degradation rates.In the present study, the degradation behavior of stacks with chromium-based interconnects (MK35x) and electrolyte-supported cells (ESC) developed at Fraunhofer IKTS is investigated. For this purpose, the initial electrochemical performance of 10-layer stacks was extensively characterized in various operating conditions in both fuel cell and electrolysis mode by electrochemical impedance spectroscopy (EIS). Degradation was evaluated during galvanostatic steady-state steam electrolysis operation over >3000 h in the temperature range of 800-825°C at a current density of -0.6 A cm-2, corresponding to a steam conversion rate of 75%. EIS analysis was used to separate the different loss contributions in the stack and showed that the ohmic resistance increase was the dominating performance degradation phenomenon. Moreover, electrochemical degradation rates in steady-state SOEL mode are compared to the ones in reversible mode with a daily cycling between electrolysis and fuel cell operation.Post-mortem analysis was carried out with scanning electron microscopy (SEM) to correlate the observed degradation phenomena with microstructural and morphological changes. The observed low degradation rates demonstrate that MK35x are ready for scale-up, and the present work gives guidance for operation strategies and stack design to extend their lifetime even further.

Accelerated Stress Testing of Solid Oxide Electrolysis Cells in a Symmetric Steam-Rich Atmosphere

Temperature, current density, steam utilization variability, and local steam starvation or excess may cause diverse degradation processes to occur in solid oxide electrolysis cells. Typical degradation mechanisms for SOEC with nickel-based fuel electrode materials include nickel migration/evaporation and agglomeration, which may lead to reduced active sites at the triple-phase boundary. However, the phenomenological cause of such degradation mechanisms is still actively debated, making the selection of a durable fuel electrode material challenging. It is desirable to understand the process by which these phenomena occur not only to minimize it, but to intentionally induce it to develop accelerated stress test protocols for cell lifetime prognostics. The degradation of solid oxide electrolyzers has been reported to be accelerated by certain stressful operating conditions. Brisse and Mocotuguy conducted a review of the degradation mechanisms of solid oxide button cells; they reported that high steam partial pressures can lead to the formation of nickel hydroxide at the cathode, which then diffuse to the surface of YSZ1. Sun et al. hypothesize that this is the main mechanism for nickel migration, due to the positive oxidation state of nickel and the direction of the electric potential2. Changes in the surface morphology of the fuel electrode due to redox cycle-induced degradation has been reported, showing the dynamics of nickel migration and agglomeration under these conditions3 . Redox cycling was found to be a destructive test protocol; efforts are currently being made by the group of Daria Vladikova to prevent fracturing of the electrodes and electrolyte during such stressful testing4. Königshofer et al. have reported through multiple investigations that protocols inducing operation at high steam conversion rates (>90%) and large current densities (0.8 A/cm2) have been effective at reproducing long-term SOEC voltage degradation5,6.The objective of this research is to establish a protocol that will help determine the causes that trigger Ni migration or evaporation, and that will mimic the electrode degradation mechanism to standardize the procedure for comparing the long-term performance of solid oxide electrolysis cells. Symmetric button cells of various fuel electrode chemistries with a diameter of 20 mm (active area 1.23 cm2) are tested under symmetric atmospheres with steam/H2 blends. The following two accelerated stress tests (AST) protocols are employed: cycling of steam partial pressure and cycling of current density. In the former, the steam molar fraction is varied from 75% to 95% in a 20-minute cycle for at least 400 cycles (i.e., 1,176 h). In the latter protocol, current density is controlled using a galvanodynamic 10-minute long cyclic ramp profile between 0.8 A/cm2 and 1.5 A/cm2 at a constant steam molar fraction between 75-95% for at least 800 cycles (i.e., 1,176 h).For all tests, the cells are operated at a constant furnace temperature between 700°C and 850°C. The performance characteristics of the various cells are expressed in terms of electrochemical impedance spectroscopy (EIS) and polarization curves every 12 h during the AST. X-ray diffraction (XRD) and fluorescence (XRF) are used to analyze the cells at beginning of life and post-mortem to identify phase changes which occur during operation. Scanning Electron Microscopy - Energy Dispersion Spectroscopy (SEM-EDS) and Glow-discharge spectroscopy (GD) are used to identify and map the nickel concentration on the cathode surface and cross-section. Preliminary results suggest that the high frequency resistance may increase by nearly 500% under a constant high-steam condition (> 90%) in a Ni-YSZ|YSZ|Ni-YSZ cell during a 200 h operation. P. Moçoteguy and A. Brisse, Int J Hydrogen Energy, 38, 15887–15902 (2013).X. Sun, T. L. Skafte, and S. H. Jensen, Fuel Cells (2021).S. Yang et al., J Alloys Compd, 921, 166085 (2022).D. Vladikova et al., Energies (Basel), 15 (2022).B. Königshofer et al., J Power Sources, 523 (2022).B. Königshofer et al., J Power Sources, 497 (2021).

Nb2CTX/graphene aerogels for efficient solar-driven steam generation

The development of high-efficiency photothermal conversion materials for seawater desalination is crucial to mitigating the global freshwater shortage crisis. The present investigation is aimed to prepare three-dimensional cylinder Nb2CTX/graphene aerogels (Nb2CTX/GAs) by a combined hydrothermal and freeze-drying process as a photothermal conversion material for solar-driven steam generation. The broad adsorption spectrum, porous microstructure, and excellent hydrophilicity account for the superior photothermal conversion performance of Nb2CTX/GAs. A high evaporation rate of 1.423 kg·m2h−1 was achieved as well as an exceptional solar steam conversion efficiency of 89.6% under one sun irradiation. Furthermore, Nb2CTX/GAs exhibited excellent cyclic stability of photothermal conversion. This work attempts to reveal the great prospect of Nb2CTX/GAs in seawater desalination applications.

Reverse Water Gas Shift versus Carbon Dioxide Electro-Reduction: The Reaction Pathway Responsible for Carbon Monoxide Production in Solid Oxide Co-Electrolysis Cells

Solid oxide co-electrolysis cells can utilize renewable energy sources for the conversion of steam and carbon dioxide into valuable chemicals and feedstocks. An important challenge in the analysis of these devices is understanding the reaction pathway(s) that govern carbon monoxide generation. Studies in which co-electrolysis polarization lies between those of pure steam and pure carbon dioxide electrolysis suggest that carbon dioxide electro-reduction (CO2ER) and the reverse water gas shift (RWGS) reaction are both contributors to CO generation. However, experiments in which co-electrolysis polarization overlaps that of pure steam electrolysis propose that the RWGS reaction dominates CO production and CO2ER is negligible. Supported by dimensional analysis, thermodynamics, and reaction kinetics, this work elucidates the reasons for which the latter conclusion is infeasible, and provides evidence for why the observed overlap between co-electrolysis and pure steam electrolysis is a result of the slow kinetics of CO2ER in comparison to that of steam, with the RWGS reaction being inconsequential. For sufficiently thin cathode current collectors, we reveal that CO2ER is dominant over the RWGS reaction, while the rate of steam electro-reduction is much higher than that of carbon dioxide, which causes the co-electrolysis and pure steam electrolysis polarization curves to overlap. This is contrary to what has been proposed in previous experimental analyses. Ultimately, this work provides insight into how to design solid oxide co-electrolysis cells such that they can exploit a desired reaction pathway in order to improve their efficiency and product selectivity.

Estimating the effect of the main design parameters on the effectiveness of high-purity hydrogen production from raw hydrocarbons in membrane catalytic devices

The paper presents the results of the application of a physically grounded mathematical model, verified through numerous practical examples, intended for estimating the effect of some design factors (membrane thickness and the system of high-purity hydrogen outlet from the under-membrane space of membrane elements) on the effectiveness and efficiency of the production of highly pure hydrogen from the products of steam conversion of hydrocarbons in advanced membrane catalytic devices.

Hydrogen Technologies: A Critical Review and Feasibility Study

Nowadays, one of the most important areas in refining the energy sector in the developed countries is the transition to environmentally friendly technologies, and hydrogen energy production is the most promising of them. In this rapidly advancing area, significant progress in creating new technologies for hydrogen fuel generation, transportation, storage, and consumption has been recently observed, while a fast-growing number of research papers and implemented commercial projects related to hydrogen makes it necessary to give their general review. In particular, the combination of the latest achievements in this area is of particular interest with a view to analyzing the possibility of creating hydrogen fuel supply chains. This paper presents an analytical review of existing methods of hydrogen production, storage, and transportation, including their key economic and energy-related characteristics, and proposes an approach to the creation, analysis, and optimization of hydrogen supply chains. A mathematical model has been developed to determine the cost of hydrogen, taking into account the supply chain, including production, transport and storage. Based on the results of modeling in the given scenario conditions for 2030, 2040 and 2050, promising hydrogen supply chains have been established. Under the various scenario conditions, hydrogen production by 2050 is most preferable by the method of steam conversion of methane with a cost of 8.85 USD/kg H2. However, due to the environmental effect, electrolysis also remains a promising technology with a cost of hydrogen produced of 17.84 USD/kg.

Thermodynamic screening of candidate ceria and perovskite systems as potential oxygen carrier materials for chemical looping water gas shift

Methane reforming and gasification processes are valuable pathways toward hydrogen production, and currently they represent nearly 79% of the worldwide hydrogen production market share. Chemical looping-water gas shift (CL-WGS) is a promising downstream process that can be integrated with reforming and gasification reactors and utilizes redox active metal oxides as oxygen exchange materials to produce separate streams of H2 and CO2. Thus, this technology can enable the production of high-purity hydrogen coupled with carbon capture without the need for an additional CO2 separation system.Although a number of redox-active metal oxides have been proposed in the literature as viable candidates for CL-WGS, the majority are based on stoichiometric metal oxides. However, non-stoichiometric oxides, which have the benefit of stability, rapid kinetics, and thermodynamic tunability, have only been proposed a handful of times. And of the prior proposed non-stoichiometric materials, none of the so called “water splitting” redox materials of the solar thermochemical H2O splitting (STCH) fields have been discussed for CL-WGS applications, despite their potentially favorable thermodynamic properties. In this research, we have identified 13 potential oxygen carrier materials and screened these for CL-WGS viability based on a simplified closed-system thermodynamic analysis. Ceria (CeO2-δ), CZO20 (Ce0.8Zr0.2O2-δ), and LSMA4060 (La0.6Sr0.4Mn0.4Al0.6O3-δ) are identified to have the most suitable properties in terms of operating temperatures, specific H2 yields, and conversions of syngas, during reduction, and steam, during oxidation. Results show that CZO20 and LSMA4060 have especially excellent reduction and oxidation extents at relatively low operating temperatures. For example, CZO20 and LSMA4060 have 85% syngas and steam conversions when cycled between 485-912 and 100–635 °C, respectively. Results show that only CZO20 is viable for isothermal operation, but higher temperatures are required; at 1023 °C, syngas and steam conversions are 80 and 12%.

STEAM CONVERSION OF ETHANOL TO HYDROGEN OVER CO-CE-O CATALYSTS

In the offered article, the reaction of steam conversion of ethanol to hydrogen over binary cobalt-chromium oxide catalysts was explored. It had been found that at temperatures up to 400°C, ethanol is mainly converted into ethyl acetate. It is shown that with increasing reaction temperature, the yield of ethyl acetate passes through a maximum. At the high temperatures of the ethanol steam reforming reaction, the main reaction product is hydrogen. The peak yield of hydrogen is detected over the catalyst Co: Ce=1:9 at 650°C and is equal to 89.9%. It has been demonstrated that carbon monoxide and methane are by-products of the reaction of the steam conversion of ethanol into hydrogen. Keywords: Ethanol conversion, binary catalysts, cerium oxide, hydrogen, ethyl acetate.

Thermal Integration of Solid Oxide Electrolysis Cell Systems with External Heat Sources to Maximize Heat Recuperation and Exergetic Efficiency

The purpose of this study is to explain the basis of thermal integration and to investigate the effects of internal and external thermal integration on the whole system performance. The basic concept of the thermal integration of SOEC system is presented while considering internal heat recuperation and coupling with external heat sources. By using temperature-heat transfer analysis, the procedure to design the optimal thermal integration of the SOEC system is described. Based on the proposed system, a parametric study with respect to stack operating conditions (i.e., stack inlet temperature, air utilization, steam conversion, hydrogen fractions) is conducted in order to elucidate their effect on the system level performance. Then, the effects of external heat sources such as steam injection, indirect heat transfer with hot fluids and heat supply by an electrical heater are examined, with pinch analysis and exergetic performance evaluation.

Performance and Degradation of Electrolyte Supported SOECs with Advanced GDC Thin-film Layers in Long-term Stack Test

Electrolyte supported Solid Oxide Cells (ESCs) with advanced thin-film Gd-doped ceria layers deposited via EB-PVD method at 600 oC were assembled and electrochemically investigated in a so-called “rainbow” stack with 30 repeat units (RUs). At the initial stage of the SOEC operation, the stack reached a high performance with an electrical efficiency of 99.65 % at 75 % steam conversion and a total power input of 1.98 kW. A long-term stack test was performed in SOEC mode for over 5000 h and demonstrated a low voltage degradation of approx. +10.9 mV·kh–1 per RU (+0.9% kh–1). The RUs with EB-PVD GDC thin-films demonstrated similar initial performance and degradation rate to the state-of-the-art cells. In this paper, the investigation mainly focuses on the electrochemical characteristics of RUs containing the EB-PVD thin-film GDC layers.

Syngas and H2 production from natural gas using CaFe2O4 – Looping: Experimental and thermodynamic integrated process assessment

Experimental methods and thermodynamic simulations were employed in this study to assess the H2 production potential of a CaFe2O4 based blue H2 production process from natural gas (NG, >90 vol%CH4). Fixed bed reactor testing was used to verify the product outcomes. Syngas production from methane using CaFe2O4 was demonstrated. Stable H2 production with high steam conversion was demonstrated with the CaFe2O4 when reduced with methane. The thermodynamic integrated process simulation enabled simulation of the process in two and three reactor configurations to understand the feasibility of a heat integrated system. The 2-reactor process used the generation of syngas as the prevailing mode for H2 generation while the 3-reactor system utilized steam water splitting in a dedicated reactor as the prevailing mode to generate H2. Simulation of the 2-reactor process's FR showed syngas generation similar to the products from fixed bed demonstrations, establishing a connection between thermodynamic simulation and experimental data. The H2 yield potentials of the various configurations were determined and compared to steam methane reforming with capture (SMR-CCS) and a Fe2O3 based system from the literature. The 2-reactor process has the potential to generate 1.6–2.1 mol of H2/mole of NG fed to the system. Three reactor configurations showed the highest potential for H2 yield with a range of 2.2–2.56 mol of H2/mole NG but with the need for additional CCS at the highest yield. A thermal management approach was introduced that combined the chemistries of CaFe2O4 and CuFeAlO4 which enabled increasing the potential yield to 2.66 mol H2/mol NG and enabling a system without the need for addition carbon capture to meet 90% threshold targets. The three reactor cases showed the most competitive performance in comparison to SMR-CCS with up to a 14.6% improvement in H2 yield.

Preparation and performance study of scalable high-efficiency solar steam generated system

Solar-driven evaporation is gaining more and more attention due to its widespread use, including desalination, power generation and solar fuel production. Among them, desalination is the most needed because water is the source of life. In this work, we have developed a new efficient and low-cost solar desalination system consisting of non-woven fabrics, carbon powder and polystyrene foam. We designed the experiments under a solar irradiation of 1000 W m−2, an ambient temperature of 25 °C and a humidity of 0.4, controlled in a laboratory performance. In this system, the solar steam conversion efficiency is greatly improved due to the fibrous structure and high absorbance of the carbonized non-woven fabric. The practical application of the system was also tested. The experimental results show that the solar steam conversion efficiency of the new system can reach 85.3% under the solar radiation intensity of 1000 W m−2. The corresponding evaporation rate is 1.23 kg (m2 h)−1. In addition, the effects of wind speed, solar irradiance, ambient temperature, and material absorptivity on evaporation efficiency are simulated. The thermal environment parameters for enhancing evaporation efficiency are given. The performance of the solar interface evaporation system is compared in terms of the first law of thermodynamics and external energy. Finally, the economics and the analysis of the device are performed, the cost of interface evaporation material is $1.05 m−2. Due to the low cost of raw materials, simple material preparation and high evaporation efficiency, the system provides the possibility for the large-scale expansion and application of solar interface evaporation.

Steam Conversion of Ethane and Methane–Ethane Mixtures in a Membrane Reactor with a Foil Made of a Pd–Ru Alloy

Steam Conversion of Ethane and Methane–Ethane Mixtures in a Membrane Reactor with a Foil Made of a Pd–Ru Alloy

Effect of Water Content on Ethanol Steam Reforming in the Nonthermal Plasma.

Ethanol steam reforming can be a source of green hydrogen. The process of producing hydrogen from ethanol is very complex. Catalysts designed for this process often become deactivated due to coke deposition. In this work, a plasma reactor was used, which is insensitive to disturbance induced by coke. The research focused on determining the influence of steam on the course of the process. The optimal water/ethanol molar ratio was found to be 4. The energy efficiency was the highest at this ratio, 22.5 mol(H2)/kW h. At the same time, a high ethanol conversion (92%) was obtained. It was also observed that the conversion of steam was many times lower than that of ethanol. However, water shortage caused a rapid increase in coke, acetylene, and ethylene production.

MXene/MnO2 nanocomposite coated superior salt-rejecting biodegradable luffa sponge for efficient solar steam generation

Solar steam generation is widely regarded as one of the potential green approaches for freshwater regeneration by utilizing solar energy. Herein, the MXene/MnO2 nanocomposite-coated biodegradable luffa sponge (Ti3C2-MnO2@LS) is proposed as an efficient solar evaporator for solar steam generation. The thin layer of Ti3C2-MnO2 coated on the surface of the luffa sponge (LS) serves as the solar absorber and enhances the hydrophilicity of the LS, while the thermally insulating LS layer with microporous structure endows sufficient water transportation and localizes heat for interfacial water evaporation. Combining MXene with MnO2 can increase the surface area as well as the stability. The Ti3C2-MnO2@LS delivers a solar evaporation rate as high as 1.36 kg m−2 h−1, with a solar steam conversion efficiency of 85.28 % under one sun irradiation. Furthermore, this Ti3C2-MnO2@LS exhibits superior salt-rejecting properties even under highly concentrated saltwater desalination and excellent wastewater purification performance. This work demonstrates the prospects of combining novel 2D materials with biomass-based materials for practical solar steam generation.

Steam Conversion of Ethane and Methane–Ethane Mixtures in Membrane Reactor with a Foil from Pd–Ru Alloy

The features of steam conversion of ethane and methane-ethane mixtures containing 5, 10 and 15% ethane in a membrane reactor with a 30 μm thick Pd–Ru foil at temperatures of 1800 and 3600 h–1 and steam/feed rations of 3 and 5 have been investigated. Comparative experiments with “non-membrane” reaction have shown that in the membrane reactor the feedstock conversion to form H2 and CO2 increases and ethane hydrocracking decreases. Increasing the rate of H2 recovery through the membrane by permeate evacuation leads to an increase in the yield of H2 and CO2. With a decrease in the steam/feed ratio from 5 to 3, the ethane hydrocracking and the rate of carbon deposits formation increases. Optimal conditions for steam conversion of ethane and methane-ethane mixtures are T = 773 K, feed space velocity of 1800 h–1 and steam/feed ratio of 5. The established regularities are similar to those obtained earlier for other types of raw materials (mixtures of methane with propane, propane, n-butane, a mixture simulating the average composition of associated petroleum gas) in this membrane reactor.

High H2 selective performance of Ni-Fe-Ca/H-Al catalysts for steam reforming of biomass and plastic

The development of a selective catalyst for the conversion of biomass and plastics into H2 by steam reforming can combat the energy crisis and global warming. In this work, support Ni-Fe-Ca/H-Al bifunctional catalysts were prepared by loading Ni and Fe into pretreatment CaO/Al2O3 (Ca/H-Al) carriers and showed high catalytic activity for the steam reforming of biomass and plastic. Moreover, the idea of bidirectional degradation was exploited to strengthen the pyrolysis of plastic with a high H/C and biomass with a high O/C. Interestingly, the products presented high H2 selective (1302.10 mL/g) and low CO2 yield (120.23 mL/g) in 7Ni-5Fe-Ca/H-Al(2:4) catalyst compared with current reports. Here, the abundant oxygen vacancies (Ov) in the H-Al carrier exhibited an electron-deficient nature, providing active sites for anchoring NiO. Meanwhile, NiO interacted with Ca2Fe2O5 to produce more defective Ov sites, which stabilized the NiO particles in the 7Ni-5Fe-Ca/H-Al (2:4) catalyst, and the interaction between the catalyst and the carrier was enhanced, leading to the reduction of weakly basic sites, this property promoted the strong adsorption of CO2 and H2O by the catalyst, contributing to the enhancement of efficient steam conversion and the promotion of conversion of by-products to H2. Notably, 7Ni-5Fe-Ca/H-Al(2:4) catalysts maintained structural integrity after regeneration and exhibited excellent regenerability in H2 selection and CO2 adsorption. The work provides a new idea for the study of efficient H2 production from steam reforming of biomass and plastics.