Looping Dry Reforming Of Methane Research Articles

Enhanced performance of La1-xFeO3-δ oxygen carrier via A-site cation defect engineering for chemical looping dry reforming of methane

Chemical looping is a process-intensification tool that focuses on the fields of fossil fuel combustion, CO2 capture, hydrocarbon valorization, energy storage, and other energy-related and environmental-related areas. Perovskite-structured LaFeO3, a typical oxygen storage material, shows great potential for chemical looping partial oxidation and H2O/CO2 splitting. Here, we report a simple and efficient strategy to enhance catalytic activity by tuning A-site cation defects in perovskites via a sol-gel method. Systematically studies show that A-site cation defects affect both the physical and chemical properties. With the A-site cation defect engineering, the crystallite size of the La1-xFeO3-δ perovskites is reduced. The catalytic performance for CH4 oxidation and CO2 splitting is enhanced with increasing oxygen vacancy concentration. The La0.93FeO3-δ oxygen carrier exhibits the highest catalytic performance with 88% CO selectivity and 90% methane conversion at 750 °C. In addition, the La0.93FeO3-δ shows higher stability in the successive CH4 partial oxidation/CO2 splitting redox cycles, with almost unchanged CH4 conversion and CO selectivity. All these results demonstrate that the strategy of adjustment of different molar ratios of A/B site in perovskite metal oxides can effectively regulate the oxygen vacancy concentration.

Boosted carbon resistance of ceria-hexaaluminate by in-situ formed CeFexAl1−xO3 as oxygen pool for chemical looping dry reforming of methane

High potential to carbon deposition over metallic Fe0 greatly limits the improvement of methane-to-syngas selectivity via chemical looping technology. Herein, we found that the in-situ formed CeFexAl1−xO3 over ceria-hexaaluminate as “oxygen pool” could greatly improve carbon resistance even with presence of Fe0. Formation of CeFexAl1−xO3 only proceeds in ceria-hexaaluminate composite while not occurs in CeO2-Fe2O3-Al2O3, which was probably originated from the strong interaction between CeO2 and the adjacent Fe and Al ions in BaFe3Al9O19 hexaaluminate structure. CeFexAl1−xO3 with outstanding oxygen ion conduction capacity was in close contact with metallic Fe0 exsoluted from Fe-hexaaluminate in a unique CeFexAl1−xO3/Fe0/hexaaluminate sandwich-like structure, which provided a convenient pathway for CeFexAl1−xO3 as “oxygen pool” to supply sufficient oxygen for in-time oxidation of carbon over adjacent Fe0. Consequently, the recycled ceria-hexaaluminate displayed both outstanding carbon resistance and high CH4 conversion (∼90%) with enhanced syngas yield that 105% and 72% higher than CeO2-Fe2O3-Al2O3 oxide and Fe-hexaaluminate, respectively.

Flame spray pyrolysis synthesized Ni-doped Fe/Ce oxygen carriers for chemical looping dry reforming of methane

The current study investigates a nano-Fe/Ce oxygen carriers (OCs) doped with Ni synthesized by flame spray pyrolysis (FSP) method for the chemical looping dry reforming of methane (CL-DRM). The thermodynamic analysis and reaction simulation of the CL-DRM process with iron-based oxygen carriers are first carried out. The result shows that when reacting with CH4, Fe2O3 is reduced to Fe3O4 at first, accompanied by generation of H2O and CO2, and then to Fe with H2 and CO production. Fe can be oxidized to Fe3O4 and FeO by CO2. Subsequently, based on the reaction patterns obtained from the aforementioned analysis, CL-DRM experiment using Ni-doped Fe/Ce oxygen carriers is conducted in a fixed-bed reactor, and the effects of different Ni doping and reaction conditions on the performance of the oxygen carriers are investigated. The OC with a Ni/Fe molar ratio of 2/98 (2NiFe) achieves over 30% CH4 conversion and 90% CO selectivity in the partial oxidation step and stable cyclic performance. The FSP process facilitates high dispersion of Ni and formation of NiCe and NiFe alloys, which are stable active sites. Moreover, the transformation of Fe oxides and CeO2 into CeFeO3 on the surface of the OC has enhanced lattice oxygen availability and further improved cyclic stability.

Migration of lattice oxygen during chemical looping dry reforming of methane with Ca2Fe2O5/Zr0.5Ce0.5O2 oxygen carrier

Ca2Fe2O5/Zr0.5Ce0.5O2 exhibits excellent reactivity in chemical looping dry reforming of methane. The migration of lattice oxygen is crucial to the cyclic stability of oxygen carrier, but the lattice oxygen migration in Ca2Fe2O5/Zr0.5Ce0.5O2 were not extensively explored. This work explored the lattice oxygen migration of Ca2Fe2O5/Zr0.5Ce0.5O2 during redox process. During the reduction process, the lattice oxygen reacted with the hydrogen radical, resulting in the decrease of lattice oxygen content and the increase of oxygen vacancy. As the lattice oxygen released, the spatial structure of Ca2Fe2O5 was destroyed and transferred into Fe8Ca8O20 with oxygen defects due to lattice distortion. The exothermic reaction between H2 and Ca2Fe2O5 promoted the formation of FeH with hexagonal close-packed structure. After reduction for 160 min, the unstable FeH completely converted into FeC with stable structure and the complete reduction was reached. As for the oxidation process, Fe and CaO reacted with the oxygen radical to form Ca2Fe2O5, leading to the complete recovery of lattice oxygen within 40 min. However, crystalline phase transformation could lead to the spatial structure instability and sintering after multiple redox cycles. Overall, the migration of oxygen during redox process is clarified in detail, providing a reference for improving the cyclic stability of Ca2Fe2O5/Zr0.5Ce0.5O2.

Regulation of metal-support interface of Ni/CeO2 catalyst and the performance of low temperature chemical looping dry reforming of methane

Interface regulation is an effective strategy to improve the interaction between carrier and active metal center, which can improve the catalytic activity and oxygen storage capacity of the catalysts. In this paper, Ni/CeO2 catalysts supported on CeO2 with different morphologies (nanorods, nanocubes, nanoctahedrons and nanopolyhedrons) were synthesized. The structure dependence of the catalysts for the low temperature chemical looping dry reforming of methane (CL-DRM) was investigated. The characterization results showed that Ni species were highly dispersed on the surface of CeO2 carrier, and some Ni ions entered the CeO2 lattice, resulting in the increase of oxygen vacancies. The Ni/ceria-rods catalyst had the highest reducibility, the most oxygen vacancies and the highest oxygen storage capacity. The irregular CeO2 nano single crystal of about 10.3 nm in the Ni/ceria-polyhedra led to high specific surface area and high reducibility which exhibited the highest redox activity and redox stability in low-temperature chemical looping dry reforming of methane at 550 °C. This study provided a new strategy for the design of efficient metal/CeO2 catalysts, which was expected to promote the application of cerium-based catalysts in chemical looping technology.

A novel Ni–MoCxOy interfacial catalyst for syngas production via the chemical looping dry reforming of methane

<h2>Summary</h2> Modulating the oxygen-metal interface that enables efficient and selective C–H activation remains challenging. Herein, we present a novel MoC_xO_y oxygen carrier for syngas production via the chemical looping CH₄–CO₂ reforming (CL-DRM) reaction. Molybdenum carbide additive induces the re-dispersion of Ni particles from Al₂O₃ surface to α-MoC driven by the strong interaction between Ni and α-MoC. A dynamic structure transformation between MoC_x and MoC_xO_y occurs and new Ni–MoC_xO_y interfaces form during the redox cycling, which is discovered to be crucial for the low-temperature CH₄ activation using surface construction experiments and <i>in-situ</i> spectroscopic methods. As a result, Ni–(α-MoC)/Al₂O₃ exhibits near 100% selectivity to syngas with a H₂/CO ratio of 2:1 at 500°C, which is a significantly lower temperature than that of conventional systems. This study first employs molybdenum carbide as an oxygen storage material (OSM) in CL-DRM reaction, paving the way of utilizing transition metal carbides as OSMs in chemical looping processes.

Operando Ce K-edge XANES Study of Low-loading Ni/CeO2 in Chemical Looping Dry Reforming of Methane

Abstract In this study, operando Ce K-edge XANES measurements of CeO2-supported Ni (Ni/CeO2) catalysts for chemical looping dry reforming of methane (CLDRM) were performed. Low-loading Ni/CeO2 was effective for selectively promoting the partial oxidation of CH4 and suppressing coke deposition. Operando XANES measurements confirmed the redox state of Ce oxide in CLDRM and revealed that the reoxidation of reduced Ce oxide during CO2 reduction was faster than the reduction of Ce oxide during CH4 oxidation.

Sandwich Ni-phyllosilicate@doped-ceria for moderate-temperature chemical looping dry reforming of methane

Chemical looping dry reforming of methane (CL-DRM) enables the highly selective oxidation of CH4 and reduction of CO2. We designed sandwich and core-shell structured 5% Ni-SiO2@Ce0.8M0.2O2-δ (M = Fe, Co, Ni) catalysts for moderate-temperature CL-DRM. Highly dispersed nano Ni particles are anchored on the surface of SiO2 spheres, and then transition metal oxide-doped CeO2 is dispersed on the inner core to form a shell layer serving as the oxygen storage role. This trilayer structure provides abundant CeO2-Ni interfaces and catalytic sites. Doping of transition metal oxides helps to activate methane for synthesis gas generation at lower temperatures. In the chemical looping cycle, the available OSC (oxygen storage capacity) was enhanced by the introduction of transition metals into ceria and follows the order of Fe-doped (2.92 mmol g−1) > Ni-doped (1.69 mmol g−1) > Co-doped (0.86 mmol g−1) > undoped (0.58 mmol g−1) catalysts. The catalyst exhibits high coke resistance and redox reactivity in successive CL-DRM redox cycles at 620 °C. In situ Drifts and Raman of CH4/CO2 temperature programmed desorption over recycled/pre-reduced catalysts show that methane is activated into CHx over highly dispersed nickel nanoparticles at 400 °C and then converted into H2 and CO by lattice oxygen. Then, oxygen vacancies are refilled, reduced species (Fe0 and Fe2+) are re-oxidized using CO2 to produce CO, and deposited carbon from CH4 POx is also removed via CO2 gasification.

Syngas production via chemical looping reforming using methane-based feed and NiO/Al2O3 oxygen carrier

Syngas production based on chemical looping reforming was experimentally studied using a fixed-bead reactor. The 15 wt% NiO/Al2O3 was used as the oxygen carrier. The reaction temperature was fixed as 800 °C. For reactant containing CH4 only, it was termed as chemical looping partial oxidation of methane (CL-POM). With five CL-POM cycles, no decay in oxygen carrier activity was found. A high H2/CO ratio resulted due to dominant H2 production reactions in the reduction stage. Carbon deposition on the oxygen carrier surface can be identified from the CO and CO2 formations in the oxidation stage. With CO2 added in the reactant in addition to CH4, this was referred to as the chemical looping dry reforming of methane (CL-DRM). Near theoretical amounts of H2 and CO yields were obtained. With both H2O and CO2 added in the reactant in addition to CH4, this was referred to as the chemical looping tri-reforming of methane (CL-TRM). Due to coupled steam reforming of methane (SRM), POM, and DRM, higher CH4 conversion, H2 and CO yields resulted compared with the CL-POM and CL-DRM cases. The average H2/CO ratio of 1.2 was obtained with reactant with molar ratio of CH4/CO2/H2O = 1/1/1.

Hydrogen production via chemical looping dry reforming of methane: Process modeling and systems analysis

AbstractThe present study presents and analyses a family of “chemical looping dry reforming” (CLDR) processes that produce inherently separated syngas (H2 and CO) streams via a combination of methane cracking in a “cracker reactor” and the Boudouard reaction (i.e., conversion of the formed carbon with CO2 to CO) in a “CO2 reactor,” and then further maximize the H2 yield via conversion of the produced CO via water‐gas‐shift. Remaining CO2 emissions are minimized via CO2 capture and sequestration. Four different configurations are evaluated which differ in how the heat required for the highly endothermic dry reforming reaction is supplied: (i) combustion of additional CH4 feed (CLDR‐CH4); (ii) combustion of some of the CO produced in the CO2 reactor (CLDR‐CO); and combustion of some of the carbon produced in the cracker reactor with (iii) pure oxygen (CLDR‐C‐oxy); or (iv) with air (CLDR‐C‐air). Process models are developed to comparatively analyze the mass and energy balances of these configurations, and benchmark them against H2‐production via conventional dry reforming and steam reforming of methane. Our results show that CLDR‐C‐oxy is the most promising H2‐production pathway among the chemical looping and conventional technologies both in terms of chemical energy efficiency and in terms CO2 emissions. Thus, the unique flexibility offered by the production of inherently separated syngas streams in CLDR enables overcoming the disadvantage of the strongly endothermic dry reforming reaction by combusting carbon internally in the reactor and thus achieving highly effective heat integration. Overall, the results support the technical viability and demonstrate the promise for strong process intensification of CLDR compared to conventional dry reforming and even steam reforming, the most widely used H2‐production pathway to‐date.

Flame Spray Pyrolysis Synthesized Ni-Doped Fe/Ce Oxygen Carriers for Chemical Looping Dry Reforming of Methane

Flame Spray Pyrolysis Synthesized Ni-Doped Fe/Ce Oxygen Carriers for Chemical Looping Dry Reforming of Methane

Chemical looping dry reforming of methane using mixed oxides of iron and cerium: Operation window

A series of the mixed oxides of iron and cerium, with an iron(III) oxide content ranging from 0 wt% to 100 wt% were tested as oxygen carriers in the chemical looping dry reforming of methane (CL-DRM). The reactivity during the CL-DRM significantly increased when iron and cerium are forming a mixed oxide. By careful control of the Fe2O3/CeO2 mass ratio, initial oxidation state and reaction time the activity of the oxygen carrier material can be adjusted so as to substantially favour oxidation of methane to syngas and discourage both total oxidation of methane and carbon deposition via decomposition of methane.

Chlorine-promoted perovskite nanocomposite as a high-performance oxygen transfer agent for chemical looping methane-assisted CO2 splitting

Metal oxide-mediated CO2 splitting with the assistance of methane (aka chemical looping dry reforming of methane) is a novel and attractive approach for CO2 utilization. Herein, we demonstrate that doping and tailoring the redox window of strontium ferrite (SrFeO3-δ)-calcium oxide nanocomposites are effective strategies to improve the performance of chemical looping reforming. The oxygen storage capacity of this redox material is about 0.82 mol O/kg. Chlorine promotes coking in the reduction step; the tailored window not only suppresses complete oxidation of methane but also enhances CO2 transformation in a fixed-bed reactor. At 980 °C, the carbon efficiency is as high as 99%, very close to the equilibrium value. In this case, no recycling or downstream separation is needed, making the proposed scheme more efficient. In addition, both the yield of CO and the productivity of syngas remain stable over 10 redox cycles. This exceptional redox performance makes the chloride-promoted SrFeO3-δ-based nanocomposites a highly competitive and cost-effective chemical looping material.

Effect of Composition on the Redox Performance of Strontium Ferrite Nanocomposite

Chemical looping dry reforming of methane is an attractive approach to use carbon dioxide and methane, the two most abundant greenhouse gases. For this scheme, the redox material (or oxygen carrier...

Ni-Fe-Al mixed oxide for combined dry reforming and decomposition of methane with CO2 utilization

The chemical looping dry reforming of methane can be used to convert greenhouse gases into products with much desirable specification. However, developing an oxygen carrier with coke-tolerance and high oxygen exchange rate usually requires the use of rare-earth metals or lanthanides. In this study, by utilizing deposited surface carbon as a reaction intermediate rather than suppressing it, complete methane conversion was possible even with the earth-abundant metal oxide particles. To establish an optimized H2/CO ratio for the hydrocarbon synthesis, the CH4 feedstock was partially replaced with CO2. By itself, Ni-Al oxide exhibited deactivation due to the agglomeration arising from methane decomposition over the redox cycle. Fe-Al oxide had stable performance over cycles, but a sudden performance decline was observed when the amount of CO2 co-feeding exceeded a certain point. Incorporating Ni into the Fe-Al oxide was found to overcome these problems. The formation of a spinel phase with Fe alleviated the agglomeration, and enhanced CH4 activation under high CO2 partial pressure. The introduction of Ni also improved carbon gasification kinetics with CO2.

Bimetallic BaFe2MAl9O19 (M = Mn, Ni, and Co) hexaaluminates as oxygen carriers for chemical looping dry reforming of methane

Chemical looping dry reforming of methane allows the continuous production of syngas and CO with decreased carbon footprint from two separated reactors, which provided system flexibility for various downstream applications, such as F-T synthesis or hydrogen purification. A key issue for this process is to find an appropriate oxygen carrier (OC) with high reactivity and recyclability. In this work, bimetallic BaFe2MAl9O19 (M = Mn, Ni, and Co) hexaaluminates were studied as OCs, with Fe-substituted BaFe2Al10O19 and BaFe3Al9O19 for comparison. The influence of Mn, Ni, and Co doping on structure, redox reactivity and stability was investigated by means of XRD, XPS, BET, H2-TPR, CH4-IR, SEM, CO2-TPO and fixed-bed experiments. Pure Fe-substituted OCs presented the coexistence of β-Al2O3 and magnetoplumbite (MP) hexaaluminate phases, which transformed from MP to β-Al2O3 during cyclic CH4/CO2 operation. Bimetallic BaFe2MAl9O19 (M = Mn, Ni, and Co) only crystallized in β-Al2O3 hexaaluminate due to the presence of +2 valent Mn, Ni, and Co, and the β-Al2O3 structure still remained stable during the CH4 reduction step. Mn doping inhibited the release of lattice oxygen, while Ni doping initiated significant CH4 pyrolysis. Among all dopants, the BaFe2CoAl9O19 OC exhibited good reactivity for syngas production with high CH4 conversion, high syngas yield, desirable H2/CO ratio (~2), and stable regenerability by CO2, taking advantages of the enhanced oxygen-donation ability and the preservation of hexaaluminate phase during successive CH4/CO2 redox cycles.

Thermodynamic analysis of syngas production via chemical looping dry reforming of methane

Chemical looping dry reforming of methane (CL-DRM) for syngas production was studied based on thermodynamic equilibrium analysis under various fuel reactor temperatures and pressures. Fe2O3 was used as the oxygen carrier (OC). Four CL-DRM stages can be identified based on the ratio of circulated Fe2O3 flow rate to fed CH4 flow rate (OC/CH4): combined methane decomposition (MD) and partial oxidation of methane (POM), combined POM and complete oxidation of methane (COM) with POM dominance, combined POM and COM with COM dominance, and COM. For syngas production the OC/CH4 ratio must be small and its value depends on reaction temperature. Based on the results obtained, it was found that CH4 oxidation due to the presence of OC is the key reaction that affects CL-DRM performance. Compared with conventional DRM in which no OC was introduced, CL-DRM has advantages of producing higher CH4 conversion and lower carbon formation. However, lower CO2 conversion results. It was found that both conventional DRM and CL-DRM were not favourable as reaction pressure increases. The CH4 conversion in CL-DRM can be enhanced by increased CO2/CH4 ratio and water addition in the feedstock. However, CO2 conversion decreased due to increased CO2 amount or enhanced water gas shift reaction.

Chemical looping dry reforming of methane with hydrogen generation on Fe2O3/Al2O3 oxygen carrier

A chemical looping dry reforming process for co-production of hydrogen and syngas was proposed. This process contains four different stages, i.e. reduction, dry reforming, steam oxidation and air oxidation. The partial oxidation of CH4 with lattice oxygen occurred along with dry reforming reaction on the reduced iron oxide in the dry reforming stage, which helps to obtain the flexibility syngas ratio and increase hydrogen yield in the next steam oxidation stages. In this study, Fe2O3/Al2O3 oxygen carrier was used to verify the feasibility of this process in a fluidized-bed reactor at 900 °C and 1.01 bar. Carbon deposition and physical properties of the carrier were studied by using O2-TPO, XRD and BET methods. It was found that the efficient conversion of CO2 and CH4 to syngas can be achieved on the reduced iron oxygen carrier. When the feed ratio of CH4/CO2 was 1 and the reduction extent of iron was 33%, the CH4 conversion and syngas yield (the output of syngas/the input of CH4) reached 98.32% and 3.84 during the dry reforming stage, respectively. Moreover, increasing the feed ratio of CH4/CO2 raised the H2/CO ratio of syngas, but the deposited carbon would form with the available lattice oxygen depleted. Finally, superior redox activity and stability were obtained during the 15 cycles, although slight sintering was observed on the reacted oxygen carrier.

Ni, Co, Fe supported on Ceria and Zr doped Ceria as oxygen carriers for chemical looping dry reforming of methane

Chemical looping dry reforming of methane (CLDRM) consists in reacting CH4 with an oxygen carrier (OC) to produce syngas and subsequently oxidizing the OC using CO2. Based on previous work on Ni/CeO2, several ceria based OCs are explored. First, different preparation methods are compared. OCs obtained by Ni impregnation on homemade ceria or coprecipitation method show similar results while the use of a commercial ceria leads to an inactive carrier. Second, Zr doping of the carrier is shown to improve the thermal stability of the material but the increased oxygen mobility promotes the total oxidation of methane instead of syngas production. Simultaneously higher amounts of coke are produced. Then, the substitution of Ni by other active elements is explored. Iron doped OC leads to very low CLDRM activity in the temperature range explored (600–800 °C). Furthermore, selectivity is negatively affected as iron oxide can contribute as oxygen carrier together with ceria, contrary to Ni or Co. Finally, substitution of Ni with Co is studied resulting in a lower reactivity towards methane. This proves to be particularly interesting at low temperature (600–650 °C) by providing good balance between surface properties for methane activation and bulk mobility of oxygen species.

Chemical looping dry reforming of methane: toward shale-gas and biogas valorization

Chemical looping dry reforming of methane (CLDRM) is performed by exposing a Ni/CeO2 to CH4 and CO2 in a cyclic way. The solid acts as oxygen carrier producing syngas (CO+H2) during exposure to CH4, and is re-oxidized during exposure to CO2. Absence of CO2 during syngas production avoids reverse water gas shift reaction and allows high selectivity. Oxygen capacity is restored and residual carbon formed at the surface is removed during exposure to CO2. In view of biogas reforming without prior separation of compounds, CLDRM is tested in presence of CO2 in the CH4 feed. CLDRM performance remains high as long as methane is in excess with respect to CO2. At 800°C, CO2/CH4 ratio up to 0.8 may be used, whereas at 600°C, CO2/CH4 should be kept below 0.4. These results allow considering direct biogas reforming in looping conditions. For shale gas valorization, the reactivity of ethane in CLDR conditions is explored. In all the explored temperature range, ethylene formation is observed. Optimization of conversion and selectivity to syngas from ethane reforming should nevertheless be possible by adapting the amount of solid and reaction conditions to the higher oxygen need for ethane reforming in comparison to that of methane.