Chemical Looping Dry Reforming Of Methane Research Articles

Microwave heating-assisted chemical looping dry reforming of methane

Chemical looping dry reforming of methane (CLDRM) offers a sustainable pathway to convert methane (CH4) and carbon dioxide (CO2) to syngas, i.e., a mixture of hydrogen (H2) and carbon monoxide (CO). However, carbon deposition caused by high gas temperature remains a crucial challenge for the CLDRM. We proposed microwave (MW) heating-assisted CLDRM to leverage the selective heating feature of MWs to create a thermal gradient between solid and gas phases. This thermal gradient, i.e., a higher solid temperature than the gas temperature, can promote desired reduction and oxidation (redox) reactions, while suppressing undesired gas phase reactions, in particular, CH4 decomposition. At bulk temperature of 800 °C, the MW heating-assisted CLDRM achieved a maximum CH4 conversion of 97% and H2/CO ratio of around 2. Compared to the conventionally heated CLDRM, the MW heating increased the redox extents of magnetite (the oxygen carrier) by 2.5 and 1.5 times, respectively, and suppressed carbon deposition.

Tailored SrFeO3-δ for chemical looping dry reforming of methane

Chemical looping dry reforming of methane (CL-DRM) is a highly efficient process that converts two major greenhouse gases (methane and CO2) into syngas ready for the feedstock of liquid fuel production. One of the major obstacles facing this technology now is creating oxygen carriers that are stable and reactive. We fabricated high-performance Sr0.98Fe0.7Co0.3O3-δ perovskite-structured oxygen carrier by combining A-site defects and B-site doping of SrFeO3-δ. During isothermal CL-DRM tests at 850 ºC, Sr0.98Fe0.7Co0.3O3-δ achieved 87.1% methane conversion and 95.2% carbon monoxide selectivity in the methane partial oxidation reaction, followed by a syngas yield of 11.6 mmol·g-1, and carbon monoxide yield of 4.16 mmol·g-1 in CO2 decomposition. A-site defect engineering of the perovskite creates abundant oxygen vacancies and enhances oxygen storage capacity (OSC). Co-doping of the B-site of Sr0.98FeO3-δ increases oxygen mobility and methane/CO2 activation, resulting in high activity in the CL-DRM process. This methodology resulted in high ionic mobility and facilitated the rapid diffusion of oxygen in the bulk phase, thereby increasing the redox properties of SrFeO3-δ. The oxygen carrier exhibits excellent structural stability and regeneration ability in successive redox cycles. This strategy offers a simple but very effective pathway to tailor OSC, oxygen mobility, and oxygen vacancies of perovskite-structured materials for chemical looping or redox-involved processes.

A nickel-modified perovskite-supported iron oxide oxygen carrier for chemical looping dry reforming of methane for syngas production

The chemical looping dry reforming of methane (CLDRM) process, which converts methane and carbon dioxide into syngas, is an environmentally friendly greenhouse gas utilization strategy. In this work, it is demonstrated that a nickel-modified perovskite-supported iron-based oxygen carrier (Ni-Fe2O3/La0.8Sr0.2FeO3) significantly enhances the reactivity of CLDRM in the temperature range of 770–800 °C while maintaining high CO selectivity and oxygen capacity, as well as good carbon deposition resistance. With the addition of nickel, the methane conversion is 52 % higher than that without nickel at 800 °C. Rational coupling of the oxygen carrier components achieves over 99 % CO selectivity. 160 consecutive isothermal cycles confirm the outstanding stability of Ni-Fe2O3/La0.8Sr0.2FeO3. Based on the experimental results and characterizations, the evolution scheme and synergistic effects between the components of the Ni-Fe2O3/La0.8Sr0.2FeO3 oxygen carrier for CLDRM reaction are proposed. The results provide a pathway for oxygen carrier design to decrease the reforming temperature while maintaining excellent reaction performance in iron-based chemical looping systems.

High-reactive and coke-resistant polyhedral NiO/Fe2O3 oxygen carrier for enhancing chemical looping CH4–CO2 dry reforming

Chemical looping dry reforming of methane (CL-DRM) is a promising technology for syngas production and efficient CH4 and CO2 utilization to provide appropriate H2/CO ratio in the reducer for Fischer-Tropsch synthesis. The crucial issue in CL-DRM is to find a highly reactive oxygen carrier (OC) with good stability. Polyhedral NiO/Fe2O3 composite oxygen carriers were successfully fabricated via a hydrothermal and calcination method based on different solubility product constants of nickel carbonate (NiCO3) and ferrous carbonate (FeCO3) in aqueous solution. The physicochemical properties of the OCs were characterized by XRD, XRF, SEM, TEM, TG/DTA, XPS, H2-TPR and Raman spectroscopy. The performance of NiO/Fe2O3 OCs was measured in a fixed-bed reactor. The experimental results indicated that the Fe2O3-0.6Ni OC has the highest syngas yield up to 90.25% with ideal H2/CO mole ratio (approximately 2) in the reducer at 750 °C. In addition, in reducing atmospheres, the Ni3Fe alloy was formed instead of metallic Ni and Fe, thus significantly improves coke resistance. Density functional theory (DFT) calculations demonstrated that the energy barrier of rate determining step of dehydrogenation process (CH3 releases H to form CH2) is 2.64 eV with OC of pure Fe2O3, which is higher than that of the condition with OC of NiO/Fe2O3 composite (2.21 eV). Therefore, the addition of NiO to Fe2O3 favors the CH4 dehydrogenation process on the surface of OCs. This study provides guidance for the design of oxygen carriers for chemical looping dry reforming of methane with the better coke-resistant property.

Syngas Production by Chemical Looping Dry Reforming of Methane over Ni-modified MoO3 /ZrO2.

We investigated supported-MoO3 materials effective for the chemical looping dry reforming of methane (CL-DRM) to decrease the reaction temperature. Ni-modified molybdenum zirconia (Ni/MoO3 /ZrO2 ) showed CL-DRM activity under isothermal reaction conditions of 650 °C, which was 100-200 °C lower than the previously reported oxide-based materials. Ni/MoO3 /ZrO2 activity strongly depends on the MoO3 loading amount. The optimal loading amount was 9.0 wt.% (Ni/MoO3 (9.0)/ZrO2 ), wherein two-dimensional polymolybdate species were dominantly formed. Increasing the loading amount to more than 12.0 wt.% resulted in a loss of activity owing to the formation of bulk Zr(MoO4 )2 and/or MoO3 . In situ Mo K-edge XANES studies revealed that the surface polymolybdate species serve as oxygen storage sites. The Mo6+ species were reduced to Mo4+ species by CH4 to produce CO and H2 . The reduced Mo species reoxidized by CO2 with the concomitant formation of CO. The developed Ni/MoO3 (9.0)/ZrO2 was applied to the long-term CL-DRM under high concentration conditions (20 % CH4 and 20 % CO2 ) at 650 °C, with two pathways possible for converting CH4 and CO2 to CO and H2 via the redox reaction of the Mo species and coke formation.

A mechanistic analysis of particle flow in a pulsatile circulating dual fluidized bed for chemical looping technology based on CDF-DEM simulation

This paper presents a three-dimensional computational fluid dynamic–discrete element method (CFD-DEM) model using Geldart class D particles for studying the fluid flow pattern in a circulating dual fluidized bed (CDFB) for chemical looping dry reforming of methane (CLDRM). The system design comprised a high-velocity air reactor (AR) also known as riser fluidized bed, a riser tube, a cyclone chamber, a fluidizing bed fuel reactor (FR), and a connecting loop, which closes the loop between AR and FR. The particles distribution, volume fraction, flow pattern, velocity and their circulation between the AR (riser) and FR (second fluidized bed) in CDFB were deeply investigated. The results showed that the CLDRM system experiences a pressure imbalance between the reduction and oxidation zones, causing solid particles to undergo a highly intricate and turbulent pulse flow. As a result, the operation of the system is alternately governed by two flow regimes: bubbling fluidization and pulsatile circulating fluidization. The burst of a high pressure pulses provide the pressure head required for circulation of the particles. The pulses also led to the intermittent transportation of particles ― in the form of particles clusters ― from high-pressure area to the region with a lower pressure.

Oxygen release and reduction kinetics of La0.35Sr0.35Ba0.3Fe1-xCoxO3 as oxygen carriers for chemical looping dry reforming of methane

Chemical looping dry reforming of methane (CL-DRM) is a viable technology by converting CH4 and CO2 to various value-added products to achieve carbon neutrality. However, it is vital for the technology to find suitable oxygen carriers with high oxygen capacity and activity. La0.35Sr0.35Ba0.3Fe1-xCoxO3 perovskite-type oxides were proposed as oxygen carriers for CL-DRM. The oxygen (O2) release property and the kinetics of La0.35Sr0.35Ba0.3Fe1-xCoxO3 reduction by CH4 were investigated via thermogravimetric analysis, O2-temperature programmed desorption and then in a fixed-bed reactor. The O2 release process of La0.35Sr0.35Ba0.3Fe1-xCoxO3 OCs can be divided into two phases. The O2 release process and corresponding rate of OCs were facilitated due to the substitution of Fe with Co in B-site. The total amounts of O2 release for these OCs were enhanced about 1.5 times from 0.445 mmol/gOC to 0.706 mmol/gOC as Co atomic fraction in B-site changes from 0 to 1. The linear correlation for high temperature phase and a volcano-curve for low temperature phase was found for the correlations among total O2 release and Co content during the O2 release process. The reduction kinetics of CH4 over OCs was described using the Avrami–Erofe'ev model (A1.5 or A2). The values of apparent activation energy (Ea) for all OCs were obtained. The results indicated the best substitution proportion of Co in La0.35Sr0.35Ba0.3Fe1-xCoxO3 OCs can be set in the range of 0.2–0.4 to emerge the excellent redox performance. The kinetics models and parameters offer valuable information for CL-DRM reactor design and further development of OCs with different A or/and B-site modifications.

Highly active La0.35Sr0.35Ba0.3Fe1-xCoxO3 oxygen carriers with the anchored nanoparticles for chemical looping dry reforming of methane

Chemical looping dry reforming of methane (CL-DRM) has the potential as a viable technology to achieve carbon neutrality in terms of converting CH4 and CO2 to various value-added products with the minimal separation requirements. However, the design and development of an appropriate oxygen carrier (OC) with the remarkable reactivity and stability make the CL-DRM process challenging. Herein, the Co-substituted La0.35Sr0.35Ba0.3Fe1-xCoxO3 (LSBFC) perovskite oxides with the anchored nanoparticles as the novel OCs were synthesized and investigated for the redox performance in the CL-DRM process. It is found that the best substitution proportion of Co in the anchored perovskite oxides can be set in range of 0.2–0.6. The optimized OCs can greatly improve the reactivity of the chemical looping process based on various characterizations. Among all samples, La0.35Sr0.35Ba0.3Fe0.6Co0.4O3 OC increases the oxygen mobility and shows a higher oxygen diffusion rate to achieve the CH4 conversion of 84.3% and syngas yield of 15.23 mmol⋅g−1 in the CH4 reduction step, respectively. A detailed analysis of the anchored perovskite oxides reveals the substitution of Co can greatly weaken the perovskite lattice to result in the migration of Fe and the formation of Fe nanoparticles, which tremendously promote the activation of CH4 for the further conversion. Furthermore, the excellent OCs also exhibit the high stability in the enhanced reaction performance, the preservation of material structure and the stable regenerability by CO2 during the successive redox cycles. These features demonstrate that the new perovskite materials with anchored nanoparticles can be the promising oxygen carriers for the CL-DRM process.

Chemical Looping Dry Reforming of Methane over Ni-Modified WO3/ZrO2: Cooperative Work of Dispersed Tungstate Species and Ni over the ZrO2 Surface

In this study, we successfully developed nickel (Ni)-modified tungstate zirconia (Ni/WO3/ZrO2) as an effective material for chemical looping dry reforming of methane (CL-DRM) under isothermal conditions (750 °C). The performance of Ni/WO3/ZrO2 strongly depended on the WO3 loading amount. The optimal amount of 10.0 wt% WO3, corresponding to low surface W density (<4 W atoms/nm2), in Ni/WO3(10)/ZrO2 resulted in the exclusive formation of dispersed tungstate species, such as isolated monotungstate and/or oligomeric polytungstate species. Increasing the loading amount to 30.0 wt% (higher surface W density (>4 W atoms/nm2)) resulted in the formation of crystalline WO3 species, diminishing the CL-DRM performance over Ni/WO3/ZrO2. Comprehensive characterization, including in situ/operando W L3-/L1-, Ni K-, and Zr K-edge X-ray absorption spectroscopy studies, revealed that surface dispersed tungstate species were reduced by CH4 to yield CO and H2, and low-valent W species assignable to W0 to W3+. The low-valent W species were reoxidized by CO2 to produce CO and regenerate the original W6+ species. These active tungstate species cooperatively work with Ni over ZrO2 surface to promote partial CH4 oxidation, leading to efficient CL-DRM.

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.

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.

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.

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.

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.

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.

Ni/CeO2 based catalysts as oxygen vectors for the chemical looping dry reforming of methane for syngas production

Chemical looping dry reforming of methane (CLDRM) is performed by exposing a Ni/CeO2 solid to CH4 and CO2 in a cyclic way. The solid acts as an oxygen vector producing syngas (CO+H2) during exposure to CH4, and is re-oxidized during exposure to CO2. Absence of CO2 during syngas production allows suppressing reverse water gas shift reaction and reaching high selectivity. Exposure to CO2 restores the oxygen capacity of the support and removes residual carbon formed at the surface, thus fully regenerating the catalyst. Solids were characterized by TPR, XRD, Raman scattering, and XPS. Results show that part of the Ni is reduced and remain in metallic state during the looping process. On the other hand, Ni2+ species in strong interaction with Ce cations are observed even after exposure to methane. Both Ni species play important roles on reactants activation and oxygen supply by the solid. Ni loading is a crucial parameter for controlling the reduction behavior of the support and therefore for CLDRM process optimization.