Chemical Looping Steam Methane Reforming Research Articles

High selectivity syngas generation by double perovskite oxygen carriers La2Fe2-xCoxO6 for chemical looping steam methane reforming

The generation of high-quality syngas combined with high-purity hydrogen is an essential challenge in the chemical looping steam methane reforming (CL-SMR) process, in which the design of oxygen carriers (OCs) is crucial. In this study, La2FeBO6 (BCr, Ni，Co) and La2Fe2-xCoxO6 (x = 0.2, 0.4, 0.6, 0.8, 1.0) double perovskites have been investigated as OCs in the CL-SMR process. Various analytical techniques (BET, XPS, XRD, H2-TPR, Raman.) have been deployed to characterize the OCs' specific surface area, crystal structure, and surface oxygen species. The fixed-bed experiments revealed that the Cr-modified perovskite had the lowest reactivity, which was attributed to the creation of LaCrO3 limiting the oxygen release rate of the OC. Meanwhile, Ni doping exhibited the maximum methane conversion (99.15 %), but it resulted in more carbon deposition due to methane cracking, and its carbon deposition was four times than that of Co doping. Whereas, the Co doped double perovskite OCs showed excellent overall performance, in which La2Fe1.8Co0.2O6 (L2F1.8Co0.2) exhibited the optimum CO selectivity (90.72 %), H2 selectivity (96.91 %), and H2 purity (96.84 %), as well as the lowest carbon deposition. Moreover, the L2F1.8Co0.2 also exhibited outstanding stability in 10 cycles, and it could be a prospective material for CL-SMR, enabling the simultaneous generation of high-quality syngas and high-purity hydrogen.

Experimental and numerical investigation of chemical-loop steam methane reforming on monolithic BaCoO3/CeO2 oxygen

Chemical looping steam methane reforming (CL-SMR) is a promising approach to co-production of syngas and hydrogen. As the CL-SMR process relies on the redox reaction of the oxygen carriers, the reactivity of oxygen carriers is crucial in the performance of CL-SMR. In this study, a monolithic BaCoO3/CeO2 oxygen carrier was synthesized, and the reaction performance was evaluated in CL-SMR. The kinetic parameters were determined based on Sestak-Berggren model, an unsteady-state CFD model was established to predict the dynamic reaction processes in three reaction stages of CL-SMR. The result suggests that the flow rate of inlet gas in reaction stages could affect the mass transfer during gas-solid reactions, and then change the evolution and distribution of reaction rate in monolithic oxygen carrier. Increasing the flow rate could improve the uniformity of reaction rate distribution and decrease the time consumption for cyclic process, but decreased the concentration of gas productions and increased the burden of gas product separation at the same time. Among three reaction stages, the conversion of oxygen carrier was accelerated with the increase of temperature, and the varied half-life time of conversions suggested that the reactivity in RS stage is intense and the reactivity in AC stage is mild.

Thermodynamic analysis of a CCHP system with hydrogen production process by methane reforming enhanced by solar-assisted chemical looping adsorption

Combined cooling, heating and power (CCHP) systems integrated with renewable energy can greatly alleviate the fossil energy crisis and greenhouse effect. This work proposes a novel CCHP system, which consists of a solar-assisted sorption enhanced chemical looping steam methane reforming (SE-CL-SMR) hydrogen generation subsystem, a solid oxide fuel cell-gas turbine (SOFC-GT) subsystem, a dual-effect Li-Br absorption chiller/heat pump (DAC/H) subsystem, and a domestic hot water (DHW) subsystem. The impacts of the reformer temperature, pressure, the ratios of steam to carbon, calcium oxide to carbon, and nickel oxide to calcium oxide on the system’s methane conversion rate, hydrogen yield, hydrogen purity, and CO2 capture efficiency are also explored. While ensuring the hydrogen production effect and considering the lowest energy consumption, the optimal reforming temperature, reforming pressure, ratios of S/C, CaO/CH4 and NiO/CaO of the CCHP system are 560 °C, 1 atm, 3, 1 and 0.5, respectively. The system’s energy and exergy analysis is performed under the optimized operating condition. In comparison with the data of reference, the findings demonstrate that the system’s overall power generation efficiency is 53.23 %, the total energy utilization rate is 74.32 %, and the exergy efficiency is 52.87 %.

Enhanced co-production of high-quality syngas and highly-concentrated hydrogen via chemical looping steam methane reforming over Ni-substituted La0.6Ce0.4MnO3 oxygen carriers

Chemical looping steam methane reforming (CLSMR) is increasingly attracting more and more attention as a promising technology for co-production of syngas and hydrogen. However, low reactivity, poor selectivity and weak resistance to carbon deposition of oxygen carriers (OCs) probably discourage further commercial application of CLSMR. With this background, a novel strategy of incorporating Ce and Ni into LaMnO3 is advised to promote lattice oxygen migration rate and improve syngas selectivity. The redox activity and cycle stability of La0.6Ce0.4Mn1−xNixO3 for CLSMR are explored in a fixed-bed reactor coupling with various characterization methods. The characterization results show that La0.6Ce0.4Mn1−xNixO3 OCs still maintain the standard perovskite structures and well-ordered skeleton. The introduction of Ce3+ induces large amounts of oxygen vacancies on the surface of OCs and improve the syngas selectivity of methane reforming, leading to higher oxygen mobility and lower carbon deposition. Meanwhile, the experimental results also confirm that the doping of Ni into La0.6Ce0.4MnO3 can greatly improve the oxygen-donation ability and effectively provide more active sites for reaction with methane. While excessive Ni in perovskite will enhance the methane dissociation, which is the main reason of carbon deposits. The proper amount of Ni doping can well match the methane activation rate to migration rate of bulk lattice oxygen that is feasible to realize the balance between productivity and efficiency. In addition, the reduced metal elements along with great amounts of oxygen vacancies together contribute to more active sites for the following steam splitting which avails to produce high-purity H2. La0.6Ce0.4Mn0.7Ni0.3O3 oxygen carrier eventually achieve syngas yield of 2.8 mmol/g H2 and 1.4 mmol/g CO that is closed to the ideal value without obvious carbon deposition, and pure H2 yield of 3.8 mmol/g, exhibiting the best redox performance and good regenerability. Meanwhile, La0.6Ce0.4Mn0.7Ni0.3O3 can still maintain high redox activity and basic perovskite structure after 15 cyclic redox tests, illustrating a desirable stability and reliability. In summary, this study offers a valuable and effective strategy to tackle with the bottleneck of CLSMR, paving the way of doping transition metal as a pathway of modulating reaction performance and stability of OCs in chemical looping processes.

Mid-temperature chemical looping methane reforming for hydrogen production via iron-based oxygen carrier particles

Chemical looping steam methane reforming (CL-SMR) via iron-based oxygen carriers is a promising method for efficient hydrogen production. To overcome challenges such as high reaction temperatures (>850 °C) and scarcity of low-cost, durable oxygen carriers (OCs), we have developed iron-based particles mixed with various ratios of nickel-based particles to achieve remarkable performance in CL-SMR at 600 °C. The mixed particles showed 85.23% methane conversion and 3.47 and 1.01 mL/min/gOC hydrogen production rates in the reduction and steam oxidation steps, respectively, in the two-step CL-SMR reaction. In the three-step CL-SMR reaction, air oxidation led to full recovery of oxygen carriers, enhancing methane conversion to 93.30% and elevating hydrogen production rate to 1.41 mL/min/gOC during steam oxidation. Precise control over methane conversion and hydrogen production in the three-step CL-SMR system is achievable by manipulating the mixing ratios of iron-based to nickel-based OC particles. Comprehensive experimental tests were conducted, covering practical aspects like support materials, gas velocity, and steam-to-carbon ratios. The outstanding cyclic stability of OC particles was confirmed over 200 consecutive redox cycles at 600 °C. The mid-temperature iron-based oxygen carrier particles, integrated with chemical looping demonstration project, might provide a powerful approach toward more efficient and scalable hydrogen production.

One-dimensional modeling of heterogeneous catalytic chemical looping steam methane reforming in an adiabatic packed bed reactor.

Hydrogen production via chemical looping steam methane reforming (CL-SMR) is among the most promising current technologies. This work presents the development in gPROMS Model Builder 4.1.0® of a 1D model of an adiabatic packed bed reactor used for chemical looping reforming (CLR). The catalyst used for this process was 18wt. % NiO with the support of Al2O3. A brief thermodynamic analysis using Chemical Equilibrium Application (CEA) was carried out to identify the optimum operating conditions. The model was simulated for 10 complete CL-SMR cycles. The effects of variations in temperature, pressure, gas mass velocity, nickel oxide concentration, reactor length, and particle diameter were studied to investigate the performance of the CL-SMR process under these variations. A parametric analysis was carried out for different ranges of conditions: temperatures from 600 to 1,000K, pressure from 1 to 5 bar, gas mass velocity between 0.5 and 0.9kg·m-2 s-1, nickel oxide concentration values between 0.1 and 1mol·m-3, particle diameters between 0.7 and 1mm, and fuel reactor (FR) lengths between 0.5 and 1.5m. At the optimum temperature (950K), pressure (1bar), and steam-to-carbon molar ratio (3/1), with an increase in particle diameter from 0.7 to 1mm, an 18% decrease in methane conversion and a 9.5% increase in hydrogen yield were observed. Similarly, with an increase in FR length from 0.5m to 1.5m, a delay in the temperature drop was observed.

Evaluation of a novel coupling process for the simultaneous production of syngas and ultra-pure hydrogen from natural gas with in situ utilization of carbon dioxide

Recently, with the aim of developing clean and efficient energy systems, various designs based on chemical looping combustion and reforming have been suggested. This study proposed and investigated the production of ultra-pure hydrogen in dual-purpose integrated zero-emission reforming (UPH2-DPIZER) process based on the sorption-enhanced chemical looping steam methane reforming (SECLSMR). This process is proposed on the basis of reduction in the emissions of carbon dioxide as well as the simultaneous generation of pure hydrogen and syngas for use in a wide range of applications. One of the most novel aspects of this research is that the proposed UPH2-DPIZER process can reduce or eliminate carbon dioxide emissions because all the produced and chemisorbed CO2 can be applied directly in the reforming process without any additional purification. Furthermore, the synthesized 30 wt%NiO-5wt.%CeO2/Al2O3 oxygen carrier was examined using the X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS) and scanning electron microscopy (SEM) techniques along with evaluation in SECLSMR process. The attained results of experimental tests are applied to adapt and validate the simulations of novel proposed process. The other objectives of this study are the reduction in required energy for the whole process along with reduction in the direct consumption of fossil fuels. The experiments showed high H2/CO molar ratio of 36 at 550 °C with appropriate methane conversion of about 74 %, while at 750 °C, nearly a complete conversion of CH4 occurs. The obtained results from the simulation of proposed UPH2-DPIZER showed the production of ultra-pure hydrogen along with syngas with H2/CO molar ratio of about 1 with negligible CO2 release.

Enhanced redox performance of LaFeO3 perovskite through in-situ exsolution of iridium nanoparticles for chemical looping steam methane reforming

Chemical looping steam methane reforming (CL-SMR) can produce high-purity hydrogen without additional separation units. However, the low reactivity of LaFeO3 oxygen carrier towards methane restricts the overall process performance. To enhance the redox activity of widely used LaFeO3 perovskite, a small amount of iridium was introduced to LaFeO3. The presence of iridium significantly enhanced both particle reduction and oxidation, and the particle preparation pathways of oxygen carriers greatly affected the long-term performance. The overall enhancement from the incorporation of iridium was demonstrated by density functional theory calculations. Despite these beneficial effects of iridium addition, surface iridium species prepared by an impregnation method were severely aggregated during successive redox cycling, leading to deactivation of the particles. In contrast, B-site incorporation of iridium leads to the exsolution of IrOx nanoparticles anchored on the perovskite host as well as to enhanced redox stability, which is essential for the long-term operation of the chemical looping process.

Double adjustment of Ni and Co in CeO2/La2Ni2-xCoxO6 double perovskite type oxygen carriers for chemical looping steam methane reforming

Chemical looping steam methane reforming (CL-SMR) is a clean and efficient technology for the co-production of syngas and hydrogen. In this work, a series of Ni and Co doped CeO2/La2Ni2-xCoxO6 double perovskite composite oxygen carriers were developed. The introduction of Co increase a large number of surface active sites, which accelerates the surface activation of CH4, while the addition of Ni provides oxygen vacancies to promote the migration of lattice oxygen in the particles. The optimal substitution ratios of cobalt and nickel are 0.6 and 1.4, respectively. The CeO2/La2Ni1.4Co0.6O6 sample exhibits excellent syngas selectivity (95%) accompanied with high methane conversion (86%) in the methane reforming stage at 850℃, and close to 100% hydrogen concentrations in the steam oxidation stage. Density functional theory calculations demonstrated that the partial oxidation of methane is a strongly exothermic process, and the double perovskite loaded with CeO2 is more conducive to the activation of CH4 and prevents the generation of carbon deposition. The Ni-Co synergistic effect formed by the appropriate doping ratio of Ni and Co can also greatly promote the partial oxidation of methane. Subsequently, the deeply reduced metals combined with oxygen vacancies provide sufficient active stable points for water vapor cracking to generate high-purity hydrogen.

Exploration of the reaction mechanism of the LaFeO3 oxygen carrier for chemical-looping steam methane reforming: a DFT study.

The CO conversion is expected to be controllable for chemical-looping steam methane reforming. Herein, density functional theory (DFT) calculations were employed to systematically explore the detailed reaction mechanism of CO conversion over the LaFeO3 oxygen carrier. It is found that the FeO2-terminated surface could exhibit better activity for CO adsorption than the LaO-terminated surface. In addition, the FeO2-terminated surface is much more favorable for CO oxidation than the LaO-terminated surface and the Fe-O site is the main active site. The oxygen diffusion process is easier to proceed on the LaO-terminated surface compared with the FeO2-terminated surface. Four pathways for the reaction process between the FeO2-terminated surface and CO were proposed and oxygen diffusion was determined as the rate-limiting step. For the reaction of CO with the LaO-terminated surface, one pathway was considered and CO2 desorption is the rate-limiting step. Comprehensively, the reactivity of CO conversion over the FeO2-terminated surface is superior to that over the LaO-terminated surface. We could control the CO conversion by regulating the oxygen activity of LaFeO3. This work provides guidance for the rational design of LaFeO3 oxygen carriers in the CL-SRM process.

Syngas production from chemical-looping steam methane reforming: The effect of channel geometry on BaCoO3/CeO2 monolithic oxygen carriers

Chemical-looping steam methane reforming (CL-SMR) is a promising technology to achieve the co-production of syngas and hydrogen. The performance of oxygen carriers in the partial oxidation of methane stage is crucial for the composition of syngas products. In this study, the performance of BaCoO3/CeO2 monolithic oxygen carrier for syngas production was investigated. The result of characterizations suggested that the oxygen carriers maintain the ideal crystal structures, the macroporous layer of BaCoO3/CeO2 adhered to monolith achieved a good energy supply and a high gas-solid contact area. To determine the reaction heat of partial oxidation of methane, the standard enthalpy of formation of BaCoO3 was measured by DSC, the obtained value was −957.794 kJ/mol. Based on the experimental result, a kinetic model of partial oxidation of methane was established, the obtained value of A and Ea were 75.902 and 74.772 kJ/mol, respectively. The effect of geometry on reaction performance was investigated by numerical simulation. It suggested increasing number of channel faces could improve the uniformity of reaction, the uniform reaction along the channel was beneficial to control the extent of reaction. Monolithic oxygen carriers need a proper geometry design to find a compromise between the heat storage for temperature control and reaction surface area.

Development and performance of CeO2 supported BaCoO3−δ perovskite for chemical looping steam methane reforming

Chemical looping steam methane reforming (CL-SMR) is a promising approach to co-production of syngas and hydrogen, and the reactivity of oxygen carriers is crucial in the performance of CL-SMR. In this study, CeO2 supported BaCoO3-δ oxygen carriers with different component distributions (labeled as dry-mix, sol-gel, co-sol-gel samples) were prepared and evaluated in CL-SMR. The BaCoO3-δ was loosely attached on CeO2 in the dry-mix sample, resulting in a high resistance to oxygen mobility and a low gas production. The co-sol-gel sample possessed impurities of Co3O4, BaCO3 and BaCeO3, which decreased reaction capacity and enhanced the secondary reaction of methane decomposition, leading to an excessive H2/CO ratio of syngas and coke formation. The contact of perovskite and CeO2 in sol-gel sample favors the synergistic effect of perovskite and CeO2, where the H2/CO ratio was close to the ideal value of 2 at 850 °C with the produced syngas and hydrogen reaching 4.57 mol/kg and 1.47 mol/kg, respectively. In situ Diffuse Reflectance Infrared Fourier Transform spectroscopy was employed to investigate the reaction mechanism of partial oxidation of methane, indicating that CH4 is gradually dehydrogenated and partially oxidized by lattice oxygen, and the conversion of -O-CH3 into -CHO and H2 is the rate-controlling step.

High syngas selectivity and near pure hydrogen production in perovskite oxygen carriers for chemical looping steam methane reforming

Chemical looping steam methane reforming (CL-SMR) provides an attractive route for hydrogen and syngas co-production through two successive steps of methane oxidation and steam splitting. However, there is also carbon formation through CH4 cracking which hampers the production of syngas (H2 and CO) and the following production of pure H2. This work prepared the perovskites La0.95Ce0.05NixFe1-xO3 (x = 0, 0.2, 0.5, 0.8, 1.0) as oxygen carriers for CL-SMR. The methane activation and steam splitting were investigated based on reactivity tests on a fixed-bed reactor and various characterizations. Results showed that La0.95Ce0.05Ni0.2Fe0.8O3 and La0.95Ce0.05Ni0.5Fe0.5O3 reached a high syngas selectivity (94.8%, 89.0%) accompanied with good methane conversion (93.1% and 95.7%) for methane partial oxidation, and near 100% hydrogen concentrations (higher than 99.6% and 99.5%) for steam splitting, indicating that additional separation step for pure hydrogen acquisition can be omitted. The H2/CO molar ratio was maintained at the optimal value of 2.0 throughout the methane partial oxidation process. Characterizations and density functional theory calculations demonstrated that methane partial oxidation was promoted via an oxygen vacancy-mediated Mars-van-Krevelen type mechanism and the partial oxidation ability of the oxygen carrier is restricted by its content of oxygen vacancy and lattice oxygen migration rate. The proper amount of Ni doping forming the NiFe synergetic effects also contributed highly to methane partial oxidation. Afterward, the deeply reduced metals combined with the oxygen vacancies provided active sites for steam splitting, hence generating pure H2.

Ni-enhanced red mud oxygen carrier for chemical looping steam methane reforming

Red mud is an iron-contained industrial waste, and the feasibility for its application in chemical looping steam methane reforming (CL-SMR) was evaluated. The Ni-enhanced red mud was prepared, and the redox reactivity, CO selectivity, H2/CO ratio, cyclic stability, and the resistance to carbon deposition and sintering were investigated. It was found that the Ni-enhanced red mud presented much higher reactivity than the unloaded one, and the red mud with NiO loading of 5 wt% (5NiO-RM) displayed the best performance with desirable reactivity and cyclic stability. For 5NiO-RM, the CO selectivity could reach 94.1%, the H2/CO ratio was 2.01, and the most suitable temperature for CL-SMR was 900 °C. Furthermore, the H2 yield in steam oxidation stage was 2.20 mmol·g−1, and the H2 purity could be up to 99.86%. The Ni could effectively activate the CH bond of methane and facilitate the transfer of lattice oxygen, leading to high reactivity. It existed in the form of metallic Ni and FeNi alloy after methane reforming stage, and most of the Ni species would developed into the FeNi spinel Ni0.4Fe2.6O4 in steam oxidation stage. Moreover, the impregnated NiO was beneficial to the particle porous structure, promoting the reactivity and redox stability.

Co-production of syngas and H2 from chemical looping steam reforming of methane over anti-coking CeO2/La0.9Sr0.1Fe1−xNixO3 composite oxides

Chemical looping steam reforming of methane (CL-SRM) is a novel process for the co-production of syngas and hydrogen without an additional purification process. However, the high activity of oxygen carriers is always accompanied by severecarbondeposition via the catalytic cracking of methane, which can result in the rapid deactivation of oxygen carriers and the production of low purity hydrogen. Herein, a series of novel composite oxide carriers of CeO2/La0.9Sr0.1Fe1−xNixO3 with varying doping ratios of Ni are developed to achieve selective and stable production of syngas and H2. The redox performance of CeO2/La0.9Sr0.1Fe1−xNixO3 was evaluated in a fixed bed reactor coupling with various analytical methods. It is found that the Ni doping ratio of 0.2 can significantly enhance the performance and stability of CeO2/La0.9Sr0.1Fe1−xNixO3. It is speculated that the proper doping ratio of Ni can simultaneously improve the surface lattice oxygen vacancies and the lattice oxygen migration rate. The CH4 reforming over CeO2/La0.9Sr0.1Fe0.8Ni0.2O3 displays a very stable performance while avoiding obvious carbon deposition within 20 min, in which, the CH4 conversion, H2 selectivity, and CO selectivity achieve 85%, 96%, and 88%, respectively. The yield of H2 (>95% purity) reaches 23 mL/min in the subsequent steam oxidation of reduced CeO2/La0.9Sr0.1Fe0.8Ni0.2O3. Its lattice oxygen can be completely recovered by the final air oxygenation. The CeO2/La0.9Sr0.1Fe0.8Ni0.2O3 exhibits high reactivity and stability in 10 redox cycles at 850 °C. These results demonstrate that the doping of Ni affords an efficient manner to regulate the lattice oxygen migration rate of perovskite oxides to match the surface reaction rate, thereby avoiding the deep reduction of surface metal ions within perovskite oxides and resulting carbon depositions during CL-SRM.

Screening loaded perovskite oxygen carriers for chemical looping steam methane reforming

Chemical looping steam methane reforming (CL-SMR) is a novel process that produce syngas and hydrogen by using solid oxygen carriers to react with methane. The selection of oxygen carriers is a key problem in the development of CL-SMR. This study screened the perovskites with different A (La, Sr) site elements, different B (Co, Fe) site elements, and different loaded materials (CeO2, ZrO2, Al2O3 and SiO2). The results showed that La in A site presented higher hydrogen production, Fe in B site could help keep the H2/CO ratio of the syngas at about 2, and CeO2 loading could achieve highest H2 purity. Thus, LaFeO3-CeO2 was screened as the optimal oxygen carrier. When WHSV was 11.79 h−1, the CO selectivity of LaFeO3-CeO2 was over 98%, H2/CO ratio of syngas was 2, and H2 purity was about 95%. The sample could recover its original crystalline phases after cyclic reactions. CeO2 could not only provide lattice oxygen for syngas production in POM stage, but also enhance the H2 production in RS stage. Furthermore, although a slight agglomeration of the sample occurred during high temperature reactions, LaFeO3-CeO2 exhibited stable reaction performance during 10 CL-SMR cycles.

Orthogonal Preparation of SrFeO3-δ Nanocomposites as Effective Oxygen Transfer Agents for Chemical-Looping Steam Methane Reforming

Orthogonal Preparation of SrFeO_3-δ Nanocomposites as Effective Oxygen Transfer Agents for Chemical-Looping Steam Methane Reforming

Nickel-iron modified natural ore oxygen carriers for chemical looping steam methane reforming to produce hydrogen

Chemical looping steam methane reforming (CL-SMR) is a promising and efficient method to produce hydrogen and syngas. However, oxygen carrier (OC) prepared by synthesis are complex, expensive and poor mechanical performance, while natural ore OCs are low activity and poor selectivity. In order to avoid these problems, Ni/Fe modification of natural ores were proposed to improve the reactivity and stability of OC to CL-SMR. The results indicated that the modified calcite recombined and improved the structural phase during the reaction, enhancing performance and inhibiting agglomeration. Moreover, high ratio of iron to nickel was easy to sinter and decline the OC performance. In addition, with the increase of steam flow, both CH4 conversion and carbon deposition decreased. Thereinto, the highest H2 concentration, CH4 conversion efficiency and H2 yield were obtained when the ratio of steam to OC was 0.05. Furthermore, CH4 flow rate had a great impact on CL-SMR performance. When the ratio of CH4 to OC was 0.04, it achieved the highest CH4 conversion efficiency of 98.96%, the highest H2 concentration of 98.83% and the lowest carbon deposition of 3.23%. However, the carbon deposition increased with the increase of CH4 flow rate. After a long-time chemical looping process, the Ni/Fe modified calcite showed a consistently stable performance with average H2 concentration of 93.08%, CH4 conversion efficiency of 88.03%, and carbon deposition of 2.15%.

Double adjustment of Co and Sr in LaMnO3+δ perovskite oxygen carriers for chemical looping steam methane reforming

As a key factor for chemical looping steam methane reforming, the oxygen carrier with high quality is essential. In this work, both high reactivity and coking resistance of the La1−xSrxMn1−yCoyO3+δ oxygen carriers are achieved by double adjustment of Co and Sr. The redox tests and characterization results showed that the introduction of cobalt provided surface active sites to accelerate the activation of methane on the surface, and the Sr doping increased the oxygen vacancies which facilitated the migration of oxygen anion in the bulk of the oxygen carrier particles. The doping of Co and Sr can match the supply of oxygen from the bulk and the need of oxygen on the surface of the oxygen carrier particles. The best substitution proportion of Co and Sr could be set in range of 0.4–0.5 and 0.2–0.4, respectively. The La0.8Sr0.2Mn0.5Co0.5O3+δ exhibited satisfactory performance and good stability in the cyclic redox tests.

Chemical looping steam methane reforming using Al doped LaMnO3+δ perovskites as oxygen carriers

Chemical looping steam methane reforming (CLSMR) is capable of co-production of high-quality syngas and pure hydrogen, and it is important to develop appropriate oxygen carriers for this process. In this work, LaMn1-xAlxO3+δ (x = 0, 0.1, 0.3, 0.5, 0.7) perovskites were investigated as oxygen carriers for CLSMR by means of characterizations and fixed-bed tests. The characterization and test results suggested that the substitution of Al leaded to more surface active sites and higher symmetry of crystal structure, which facilitates the activation of methane molecule on the surface and the formation of the oxygen vacancy in the bulk of the oxygen carrier particles, increasing the release rate of selective oxygen and the yield of syngas. The yield of CO2 declined with the Al doped proportion due to the decrease of the mount of Mn4+ and surface absorbed oxygen. The substitution of Al cations could stabilize the crystal structure and prevent the destruction of perovskite structure. No carbon formed on LaMn1-xAlxO3+δ with x from 0 to 0.5 and a long period of partial oxidation was achieved to produce high-quality syngas with the H2/CO ratio of 2 and pure hydrogen, while carbon deposition occurred on the LaMn0.3Al0.7O3+δ oxygen carrier. LaMn0.5Al0.5O3+δ possessed the best performance with CO selectivity of 96.4%, the CO yield of 1.70 mmol·g−1, the H2 yield of 3.32 mmol·g−1 in the reduction stage and the H2 yield of 1.98 mmol·g−1 in the oxidation stage on average in 20 cyclic redox tests. LaMn0.5Al0.5O3+δ exhibited good thermal stability and cyclic performance. It can be deduced that LaMn0.5Al0.5O3+δ perovskite is a potential oxygen carrier for cyclic CLSMR.