Chemical looping gasification (CLG) of biomass uses the lattice oxygen of oxygen carriers to convert biomass into syngas with a low tar content, high heating value, and low price. It is of key importance to exploit well-dispersed and thermally stable oxygen carriers for the CLG process. In the current work, a series of oxygen carriers with varied Fe and Ni molar ratios were synthesized from hydrotalcite compound precursors (HTlcs), which made the metallic elements mix at the molecular level. Consequently, highly dispersed complex metal oxygen carriers can be achieved after precursor calcinations. CLG of biomass char was carried out in TGA and a fixed bed reactor accompanied by various physical and chemical analyses for the fresh and used oxygen carriers. The result manifested the HTlcs crystalline form, which was formed in the precursors and produced the Fe0.99Ni0.6Al1.1O4 compound after calcination, suggesting that a high degree dispersion of the multimetal oxygen carrier was synthesized. The main H2 uptake and CLG reactivity of the oxygen carriers were related to its higher metal dispersion and synergistic effect between Fe and Ni. Accordingly, there was an optimum Fe/Ni ratio of 4:1 in oxygen carriers at which the oxygen carrier can achieve better CLG reactivity. Also, the oxygen carrier to biomass char mass ratio of 7:3 provided a maximum weight loss of 35.59% and a largest mass loss rate of 2.46 wt %/min, suggesting higher lattice oxygen releasing efficiency. CO exhibited a higher generating rate in the CLG reactions owing to its higher reaction activation energy with lattice oxygen [O], while H2 was more prone to being consumed. The morphological analysis of fresh and regenerated samples exhibited that the oxygen carrier was reduced to the Fe3Ni2 alloy phase after the CLG process, and the lattice oxygen can be fully recovered in an air atmosphere. Although the BET surface displayed a decreased trend in the regenerated oxygen carriers, serious sintering was not observed in the samples, and the main metallic crystallized phases were still maintained.

Double-perovskite type oxide LaSrFeCoO6(LSFCO) was used as oxygen carrier for chemical looping steam methane reforming (CL-SMR) due to its unique structure and reactivity. Two different oxidation routes, steam-oxidation and steam-air-stepwise-oxidation, were applied to investigate the recovery behaviors of the lattice oxygen in the oxygen carrier. The characterizations of the oxide were determined by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), hydrogen temperature-programmed reduction (H2-TPR) and scanning electron microscopy (SEM). The fresh sample LSFCO exhibits a monocrystalline perovskite structure with cubic symmetry and high crystallinity, except for a little impurity phase due to the antisite defect of Fe/Co disorder. The deconvolution distribution of XPS patterns indicated that Co, and Fe are predominantly in an oxidized state (Fe3+ and Fe2+) and (Co2+ and Co3+), while O 1s exists at three species of lattice oxygen, chemisorbed oxygen and physical adsorbed oxygen. The double perovskite structure and chemical composition recover to the original state after the steam and air oxidation, while the Co ion cannot incorporate into the double perovskite structure and thus form the CoO just via individual steam oxidation. In comparison to the two different oxidation routes, the sample obtained by steam-oxidation exhibits even higher CH4 conversion, CO and H2 selectivity and stronger hydrogen generation capacity.Download high-res image (136KB)Download full-size image Chemical looping steam methane reforming (CL-SMR) is a novel and promising technology for syngas and hydrogen co-production using double-perovskite oxide as oxygen carrier.

•Substitution of Sr is beneficial to the formation of metal with high valence state.•Coexistence of multi-metals synergistically promotes the oxygen diffusion.•The CL-SMR reaction boundary stays on the surface of the double perovskite oxides.•Lattice oxygen transfers from the bulk to boundary to take part in the reaction.•The reduced metals in active sites gradually transfer inward the bulk.Co-production of syngas and hydrogen via chemical looping steam methane reforming (CL-SMR) using double perovskite-type oxide La1.6Sr0.4FeCoO6 as an oxygen carrier was studied. The reaction mechanisms, including the synergistic effects, the metal transitions, the oxygen diffusion and the migration of reaction boundary during the two-step reactions, were systematically investigated by the characterizations of the oxygen carriers at different reaction stages using XRD, XPS, H2-TPR and TG technologies. Meanwhile, isothermal reactions were carried out in a fixed-bed reactor to analysis the reaction products. Three reaction stages including the total oxidation of methane with the active adsorbed oxygen, partial oxidation of methane with the lattice oxygen, and the methane decomposition were identified, using the surface of the oxygen carrier particles as reaction boundary. A large number of syngas was generated due to the concordant of methane dissociation with the lattice oxygen diffusion, and the resistant to coke formation was enhanced effectively. In the steam dissociation stage, the deep reduced metals (Fe2+ and Co0) combining with the abundant oxygen vacancies provided enough active sites for the breakage of HO bond of H2O. The oxygen vacancies were neutralized immediately by the O atom, and the two H atoms combined together to form amounts of H2. These results suggested that, the positive roles displayed by the synergistic effects between multi-metals in double perovskite structure could effectively promote the partial oxidation of methane and steam splitting. It provides a potential way to develop more active oxygen carrier for CL-SMR to co-produce syngas and hydrogen by comprehensively considering the methane dissociation and the lattice oxygen diffusion.Download high-res image (158KB)Download full-size image

•The gasification performance of sewage sludge CLG with iron ore was investigated.•Natural hematite can provide the required oxygen for sludge gasification.•An optimal equivalent coefficient, temperature and steam content were determined.•Sludge conversion showed an uptrend with the increase of cycle numbers.•Sludge ash revealed a physical effect rather than a chemical effect on the hematite.Chemical looping gasification (CLG), with inherent characteristic of low pollutant emissions can realize the treatment and disposal principle of sewage sludge of harmlessness, reduction, stabilization and reutilization. This work attempted to investigate the feasibility of CLG of sewage sludge with hematite oxygen carrier. The role of hematite in CLG was firstly determined and it was used as gasification agent to provide the required oxygen for sludge conversion. Subsequently, the effect of various operating parameters on sludge CLG was discussed. An optimal mass ratio of sludge to hematite oxygen carrier was determined at 0.33 to achieve the high-efficient conversion of sludge. The reaction temperature of sludge gasification was set at 900 °C to avoid the excessive reduction of hematite. Suitable steam content was assigned to at 19.52%, where the sludge conversion attained the maximum. Ash deposited caused the decrease of specific surface area of hematite, but the accumulated mineral elements in sludge ash can improve the reactivity of oxygen carrier. Additionally, the ash accumulation also can prolong the gas mean residence time. Hence, the sludge conversion showed a slight uptrend with the cycle numbers. The phosphorus element of sludge was formed of CaH2P2O7 and CaHPO4 during the CLG. Although some sludge ash deposited on the surface of hematite particles, the new compounds were not observed in the reacted oxygen carrier. Additionally, sludge ash has a relatively high resistance trend for bed agglomeration and deposit formation due to the high content of Ca/Al elements. Consequently, the accumulation of sludge ash only reveals physical effects rather than chemical effects on the hematite particles. Thus, it is easy to separate the sludge ash from hematite particles according to the differences in density and size.

•The reactivity of NiFe2O4 oxygen carrier (OC) with biomass char was investigated.•NiFe2O4 OC shows an excellent performance due to the synergistic effect of Fe/Ni.•An optimum OC to biomass char mass ratio and suitable steam content was determined.•An acceptable decrease of NiFe2O4 OC reactivity is observed within 20 cycles (64 h).•Structural collapse and BET surface area decrease lead to the deactivation of OC.Chemical looping gasification (CLG) involves the use of an oxygen carrier (OC) which transfers oxygen from air to solid fuel to convert the fuel into synthesis gas, and the traditional gasifying agents such as oxygen-enriched air or high temperature steam are avoided. In order to improve the reactivity of OC with biomass char, facilitating biomass high-efficiency conversion, a compound Fe/Ni bimetallic oxide (NiFe2O4) was used as an OC in the present work. Effect of OC content and oxygen sources on char gasification were firstly investigated through a TG reactor. When the OC content in mixture sample attains 65 wt.%, the sample shows the maximum weight loss rate at relatively low temperature, indicating that it is very favorable for the redox reactions between OC and biomass char. The NiFe2O4 OC exhibits a good performance for char gasification, which is obvious higher than that of individual Fe2O3 OC and mechanically mixed Fe2O3 + NiO OC due to the Fe/Ni synergistic effect in unique spinel structure. According to the TGA experimental results, effect of the steam content and cyclic numbers on char gasification were investigated in a fixed bed reactor. Either too low steam content or too high steam content doesn't facilitate the char gasification. And suitable steam content of 56.33% is determined with maximum carbon conversion of 88.12% and synthesis gas yield of 2.58 L/g char. The reactivity of NiFe2O4 OC particles shows a downtrend within 20 cycles (∼64 h) due to the formation of Fe2O3 phase, which is derived from the iron element divorced from the Fe/Ni spinel structure. Secondly, the sintering of OC particles and ash deposit on the surface are also the reasons for the deactivation of NiFe2O4 OC. However, the carbon conversion and synthesis gas yield at the 20th cycle are still higher than those of the blank experiment. It indicates that the reactivity of NiFe2O4 OC can be maintained at a relatively long time and NiFe2O4 material can be used as a good OC candidate for char gasification in the long time running.

•The reactivity of iron ore with char was investigated in a fixed bed reactor.•Steam, as gasification agent, can evidently improve the biomass char conversion.•An optimized mass ratio of iron ore to char and steam content were determined.•An acceptable decline of iron ore reactivity was observed after 20 cycles (52 h).•The decrease of iron ore reactivity is ascribed to sintering and ash deposition.Chemical looping gasification (CLG), employing the oxygen carriers to replace the gasification agents for solid fuels gasification, is viewed as a promising gasification technology thanks to its low cost for producing high quality synthesis gas. In the present work, natural iron ore is applied as an oxygen carrier for CLG of biomass char in a fixed-bed reactor. The Redox reactions between biomass char and iron ore can occur even under inert atmosphere, but the char conversion is low due to inadequate contact of solid–solid phases, resulting in a low reaction rate. In order to improve the char conversion rate, mixture of steam and iron ore is used as gasification agent in the CLG of biomass char. An optimal mass ratio of oxygen carrier to biomass char and a suitable amount of steam addition are determined. It is observed that biomass char gasification with the mixture of iron ore and steam increases the carbon conversion by 80%, and attains three times gas yield as much as the char gasification with individual iron ore. The cyclic performance of iron ore is also discussed. The carbon conversion and gas yield shows a mild downtrend with the increase of cycle numbers due to a slight decrease of specific surface area of oxygen carrier, caused by the thermal sintering and ash deposition. However, iron ore still maintains a satisfactory reactivity after 20 cycles (∼52 h), indicating that it is a good oxygen carrier candidate for char gasification.

The objective of this paper is to systematically investigate the influences of different preparation methods on the properties of NiFe2O4 nanoparticles as oxygen carrier in chemical looping hydrogen production (CLH). The solid state (SS), coprecipitation (CP), hydrothermal (HT), and sol–gel (SG) methods were used to prepare NiFe2O4 oxygen carriers. Samples were characterized by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Brunauer–Emmett–Teller (BET) surface area measurement, as well as Barrett–Joyner–Halenda (BJH) porosity test. The performance of the prepared materials was first evaluated in a TGA reactor through a CO reduction and subsequent steam oxidation process. Then a complete redox process was conducted in a fixed-bed reactor, where the NiFe2O4 oxygen carrier was first reduced by simulated biomass pyrolysis gas (24% H2 + 24% CO + 12% CO2 + N2 balance), then reacted with steam to produce H2, and finally fully oxidized by air. The NiFe2O4 oxygen carrier prepared by the sol–gel method showed the best capacity for hydrogen production and the highest recovery degree of lattice oxygen, in agreement with the characterization results. Furthermore, compared to individual nickel ferrite particles, the mixture of NiFe2O4 and SiO2 presented remarkably higher stability during 20 cycles in the fixed-bed reactor. The structural and morphological stability of samples after reactions was also examined by XRD, XPS, and SEM analyses.

Double-perovskite type oxide LaSrFeCoO6 was used as oxygen carrier for chemical looping steam methane reforming (CL-SMR) due to its unique structure and reactivity. Solid-phase, amorphous alloy, sol-gel and micro-emulsion methods were used to prepare the LaSrFeCoO6 samples, and the as-prepared samples were characterized by means of X-ray diffraction (XRD), hydrogen temperature-programmed reduction (H2-TPR), X-ray photoelectron spectroscopy (XPS), Brunauer-Emmett-Teller (BET) surface area. Results showed that the samples made by the four different methods exhibited pure crystalline perovskite structure. The ordered double perovskite LaSrFeCoO6 was regarded as a regular arrangement of alternating FeO6 and CoO6 corner-shared octahedra, with La and Sr cations occupying the voids in between the octahedral. Because the La3+ and Sr2+ ions in A-site did not take part in reaction, the TPR patterns showed the reductive properties of the B-site metals. The reduction peaks at low temperature revealed the reduction of adsorbed oxygen on surface and combined with the reduction of Co3+ to Co2+ and to Co0, while the reduction of Fe3+ to Fe2+ and the partial reduction of Fe2+ to Fe0 occurred at higher temperatures. From the point of view of the oxygen-donation ability, resistance to carbon formation, as well as hydrogen generation capacity, the sample made by micro-emulsion method exhibited the best reactivity. Its redox reactivity was very stable in ten successive cycles without deactivation. Compared to the single perovskite-type oxides LaFeO3 and LaCoO3, the double perovskite LaSrFeCoO6 exhibited better syngas and hydrogen generation capacity.Catalytic performance of sample ME in ten cycles (a) Methane reduction stage; (b) Steam oxidation stage

•Fe2O3/NiO oxygen carrier was used for CLG of biomass in 10 kWth CFB.•The gasification efficiency of system reached to 70.48%.•Ni–Fe kamacite was generated in redox cycles to help improve reactivity.•Fe–Ni bimetallic OC showed stable CLG performance with better reactivity.Chemical-looping gasification (CLG) of biomass was investigated in a 10 kWth interconnected fluidized-bed reactor with Fe–Ni bimetallic oxides as oxygen carriers (OC). The thermodynamic analysis of the CLG indicated that the temperature range of 700 °C–950 °C can be suitable for the CLG reactions. The fluidized bed experimental results indicated that biomass was partially oxidized to synthesis gas by the lattice oxygen of the oxygen carrier in the fuel reactor and the synthesis gas composition of CO, H2 and CH4 as well as carbon conversion rate and gasification efficiency increased with the rising reaction temperature, while the CO2 fractions decreased due to the exothermic process. Carbon conversion decreased with the rising ratio of biomass to oxygen carrier. However, there was an optimal value of the gasification efficiency at 70.48% corresponding to the feeding rate of 1.6 kg/h. Compared to the Fe2O3/Al2O3 oxygen carrier, the Fe–Ni bimetallic oxygen carriers displayed a higher the gasification efficiency of biomass, which was correlated with the increasing composition of CO, H2 caused by the synergistic effect between Fe2O3 and NiO. The fresh and used oxygen carriers were characterized by means of XRD, SEM/EDX and BET. The XRD results indicated the mainly reduction products of the oxygen carrier were Fe3O4 in the CLG of biomass and new phase of Ni–Fe kamacite was formed during redox cycles, which could improve the reactivity of the oxygen carrier. Also, the oxygen carriers can be well regenerated and kept good crystalline state. The surface area of the oxygen carrier decreased from 2.486 m2/g to 2.085 m2/g after 120 min CLG reactions. The average pore diameter and total pore volume shifted from 39.8 nm, 0.0248 cc/g to 39.4 nm, 0.0205 cc/g, respectively, suggesting that a part of micorpores in the particles of the oxygen carrier were blocked or collapsed. However, reactivity deterioration of the Fe–Ni bimetallic oxygen carrier was not observed during the experiment operation. SEM-EDX results showed that the metal elements were distributed uniformly in the fresh and used oxygen carriers and irregularly blocky particles with smaller average size and porous structure were still present in regenerated oxygen carrier samples. Overall, these results suggested that the Fe–Ni bimetallic oxygen carrier was a good candidate for the CLG of biomass.

Chemical looping gasification (CLG) was investigated in a 10 kWth interconnected fluidized bed reactor with Fe2O3/Al2O3 as oxygen carriers (OC) and pine sawdust as fuel. The effects of the operation temperatures and sawdust feeding rate on the gas composition, cold gas efficiency, and carbon conversion rate of biomass were investigated. The fresh and used oxygen carrier particles were characterized by means of XRD, SEM, and BET. The results indicated that the sawdust was partially oxidized to syngas by lattice oxygen from the oxygen carrier. The syngas yield, cold gas efficiency, and carbon conversion increased with increasing operating temperature. Also, the concentrations of CO, H2, and CH4 in the syngas increased at the elevated temperature, while the CO2 fraction decreased. The feeding rate of biomass has a significant impact on the syngas composition and cold gas efficiency. There was an optimal value of feeding rate at 2.24 kg/h corresponding to the maximum cold gas efficiency in the tested reactor system. XRD analysis showed that the oxygen carrier particles were reduced to Fe3O4 from Fe2O3 in the course of the CLG reactions. BET results indicated the surface area, total pore volume, and average pore size of the oxygen carrier particles increased initially and then slightly decreased with the reaction proceeding, due to the interstice and thermal sintering. However, the OC samples were well regenerated and maintained a good crystalline state after 60 h of operation, which illustrated that the synthesized oxygen carrier had a stable reactivity and good resistance to agglomeration.

Chemical looping gasification (CLG) is considered as a novel gasification technology because gas-phase oxygen of the gasifying medium can be replaced by lattice oxygen of the oxygen carrier. The gasifying mediums (e.g., pure O2 and steam) used as the oxygen source can apparently improve the char conversion in traditionally biomass gasification. Similarly, the objective of this study is to investigate char CLG with the oxygen carrier as an individual oxygen source. A NiO-modified iron ore oxygen carrier was prepared by the impregnation method coupled with ultrasonic treatment. The characteristics of the oxygen carrier were analyzed by an X-ray diffractometer (XRD) and H2 temperature-programmed reduction (H2-TPR). The formation of spinel-type nickel iron oxide NiFe2O4 can evidently enhance the reactivity of the oxygen carrier. The reduction of the oxygen carrier by biomass char was investigated using thermogravimetric analysis (TGA) together with a fixed-bed reactor under an inert atmosphere. TGA tests show that the reactivity of the oxygen carrier increased with the increase of NiO loading. An optimal mass ratio of char/oxygen carrier is determined at 4:6 with the aim of obtaining a maximum reaction rate. The presence of spinel-type nickel iron oxide NiFe2O4 apparently improved the reaction rate of char gasification. The fixed-bed gasification results show that CO was generated faster than other components because carbon was partially oxidized and H2 was quickly consumed by the lattice oxygen [O] of the oxygen carrier. A relatively high carbon conversion of 55.56% was obtained in the char CLG, in comparison to that of char pyrolysis (5.52%). The lattice oxygen [O] of the oxygen carrier was fully consumed by biomass char. Moreover, biomass char was catalytically pyrolyzed becausee the deep reduction products (metallic iron and nickel) can act as catalysts for char pyrolysis. XRD analysis shows that the oxygen carrier was deeply reduced into Fe (Ni) alloy and Fe3C species during the reduction stage of char CLG. However, the regenerated oxygen carrier after oxidation can be recycled for char CLG on the basis of XRD and scanning electron microscopy (SEM) analyses.

•Biomass gasification using chemical looping was studied with iron ore oxygen carrier.•Oxygen carrier possesses a similar performance with steam for biomass gasification.•An optimum molar ratio of Fe2O3/C was maintained at 0.23 for maximum gas yield.•The reactivity of oxygen carrier was gradually decreased with the reduction time.Experiments regarding to biomass gasification using chemical looping (BGCL) were carried out in a fluidized bed reactor under argon atmosphere. Iron ore (natural hematite) was used as an oxygen carrier in the study. Similar to steam, a performance of oxygen carrier which provided oxygen source for biomass gasification by acting as a gasifying medium was found. An optimum Fe2O3/C molar ratio of 0.23 was determined with the aim of obtaining maximum gas yield of 1.06 Nm3/kg and gasification efficiency of 83.31%. The oxygen carrier was gradually deactivated with reduction time increasing, inhibiting the carbon and hydrogen in biomass from being converted into synthesis gas. The fraction of Fe2+ increased from 0 to 47.12% after reduction time of 45 min, which implied that active lattice oxygen of 49.75% was consumed. The oxygen carrier of fresh and reacted was analyzed by a series of characterization methods, such as X-ray diffraction (XRD), Scanning electron microscopy (SEM), and Energy-dispersive X-ray spectroscopy (EDX).

Chemical-looping reforming (CLR) is a technology that can be used for partial oxidation and steam reforming of hydrocarbon fuels. It involves the use of a metal oxide as an oxygen carrier, which transfers oxygen from combustion air to the fuel. Composite oxygen carriers of cerium oxide added with Fe, Cu, and Mn oxides were prepared by co-precipitation and investigated in a thermogravimetric analyzer and a fixed-bed reactor using methane as fuel and air as oxidizing gas. It was revealed that the addition of transition-metal oxides into cerium oxide can improve the reactivity of the Ce-based oxygen carrier. The three kinds of mixed oxides showed high CO and H2 selectivity at above 800 °C. As for the Ce−Fe−O oxygen carrier, methane was converted to synthesis gas at a H2/CO molar ratio close to 2:1 at a temperature of 800−900 °C; however, the methane thermolysis reaction was found on Ce−Cu−O and Ce−Mn−O oxygen carriers at 850−900 °C. Among the three kinds of oxygen carriers, Ce−Fe−O presented the best performance for methane CLR. On Ce−Fe−O oxygen carriers, the CO and H2 selectivity decreased as the Fe content increased in the carrier particles. An optimal range of the Ce/Fe molar ratio is Ce/Fe > 1 for Ce−Fe−O oxygen carriers. Scanning electron microscopy (SEM) analysis revealed that the microstructure of the Ce−Fe−O oxides was not dramatically changed before and after 20 cyclic reactions. A small amount of Fe3C was found in the reacted Ce−Fe−O oxides by X-ray diffraction (XRD) analysis.

Three-dimensionally ordered macroporous (3DOM) LaFe0.7Co0.3O3 perovskite-type oxides were synthesized using a polystyrene (PS) colloidal crystal templating method. The obtained 3DOM LaFe0.7Co0.3O3 perovskites were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and Brunauere-Emmette-Teller (BET) surface area. Its performance as oxygen carriers in chemical looping steam methane reforming (CL-SMR) to produce syngas (H2 + CO) and hydrogen were investigated in a fixed-bed reactor. The size of PS spheres obviously increases as the styrene addition increases. The calcination temperature is the major factor to affect the prepared 3DOM perovskite. SEM and TEM analysis show that the samples calcined at 500, 800 and 850°C exhibit good 3DOM structures which collapse when the sample is calcined at 900°C. XRD results suggest that the obtained 3DOM LaFe0.7Co0.3O3 perovskites are pure crystalline. Two kinds of oxygen species, bulk lattice oxygen and surface adsorbed oxygen, are found to exist on the 3DOM LaFe0.7Co0.3O3 perovskites. The surface oxygen contributes to the complete oxidization of methane to CO2 and H2O in beginning of the reaction, while the bulk lattice oxygen tends towards partial methane oxidation to H2 and CO. In the methane conversion step, methane is partially oxidized into syngas at a H2/CO molar ratio close to 2:1 by the 3DOM-LaFe0.7Co0.3O3 in a wide range of the reactions, suggesting that the sample exhibits a good resistance to carbon deposition. In the steam oxidation step, the reduced perovskites are oxidized by steam to generate hydrogen with hydrogen productivity about 4 mmol/g oxygen carriers.

Polystyrene spheres were prepared by soap free emulsion polymerization method, then three dimensional ordered macroporous (3DOM) oxides Fe2O3 were successfully prepared after impregnation and calcination using nitrates as raw materials and citric acid as complexing agent. The samples were characterized by the techniques of scanning electron microscopy (SEM), X-ray diffraction (XRD), BET and mercury porosimetry. Pyrolysis and gasification of biomass with Fe2O3 as oxygen carriers in helium atmosphere were carried out in a thermogravimetric analyzer coupled with mass spectrometry (TG-MS). The possibility of 3DOM Fe2O3 functioning as gasification agent in biomass gasification substituted for pure oxygen, oxygen-enriched air or steam were investigated. Furthermore, a comparison experiment was carried out by using analytically pure Fe2O3 to analysis the high-performance of 3DOM Fe2O3. The characterization results showed that 3DOM Fe2O3 presented 3DOM morphology and the tiers were arranged alternatively and connected through three-dimensional pore structures. 3DOM Fe2O3 prepared was pure Fe2O3 and no other impurity phases existed when contrast with the XRD pattern of analytically pure Fe2O3, TG-MS results showed that Fe2O3 contributed to biomass gasification in high temperature stage. When used 3DOM Fe2O3 as oxygen carrier, the maximum weight loss and maximum weight loss rate raised 7.1% and 0.29%/min in the gasification stage, respectively, meanwhile two generation peaks of CO, CO2, and CH4 appeared in the MS curves.

Chemical-looping steam methane reforming (CL-SMR) is a novel method proposed on the base of chemical looping combustion (CLC) technology. In the CL-SMR scheme, methane is partially oxidized to syngas (H2/CO=2.0) by the lattice oxygen in reformer reactor in the absence of gaseous oxidant, and then the reduced oxygen carrier is oxidized by steam to produce hydrogen in steam reactor. The use of perovskite type oxide LaFeO3 as an oxygen carrier in CL-SMR was studied. While the basicity of CaO/MgO modified oxygen carriers, LaFeO3-CaO and LaFeO3-MgO, were also synthesized aiming to increase specific surface area, thermostability, and resistance to coke formation. The synthesized oxides were characterized by X-ray diffraction (XRD), H2-temperature-programmed reduction (H2-TPR), Brunauer-Emmett-Teller (BET) surface area and X-ray photoelectron spectroscopy (XPS). Three oxygen carriers exhibited high active and selective for syngas production from methane, and maintained perovskite type over cyclic redox operations. The LF-CaO sample is the best candidate for the CL-SMR of the three samples judging from the reactivity, selectivity, and resistance to carbon formation. It showed good regenerability during 5 redox reactions.

•Double perovskites exhibit high reactivity and stability for CL-SMR.•Substitution of A site metal obviously affects the valence states of B/B′ sites.•The metal cations and the oxygen vacancies coordinately control the reactivity.•La0.6Sr0.4FeCoO6 shows the best capacity for oxygen transport and steam splitting.Chemical looping steam methane reforming (CL-SMR) is a potential route to efficiently co-produce syngas and hydrogen. Development of oxygen carrier with high activity, good recyclability, strong resistance to carbon deposition and excellence capacity for steam splitting is highly desired for this process. The article investigated a novel and unique structure of double perovskite-type oxides La1−xSrxFeCoO6 (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0) as oxygen carrier. XRD, XPS and H2-TPR technologies were adopted to characterize the physical and chemical properties of them. Meanwhile, isothermal reactions and cyclic redox reactions were carried out in a fixed-bed reactor to determine the influences of Sr-substitution on the reactivity of La1−xSrxFeCoO6. XRD results confirmed the formation of double perovskite crystal structure for all the samples, while substitution of Sr induced a certain degree of Fe/Co disorder generating oxygen vacancies and/or higher oxidation states of metal cations. Synergistic interactions between surface metal ions, such as Fe4+/Fe5+ with Co3+ which were detected by XPS, strongly enhance the reducibility of oxygen carriers. Three zones including total oxidation of methane by surface oxygen, partial oxidation of methane by lattice oxygen and carbon deposition were divided. Among the six samples with different substitution of Sr, La0.6Sr0.4FeCoO6 exhibited the best oxygen transport ability, thermal stability, as well as capacity for hydrogen generation. A stable CH4 conversion at ∼90% with desired H2/CO ratio at 2.0–2.5 in the methane reduction stage, and an average hydrogen yield at ∼5.9 mmol/g oxygen carrier with ∼93.8% of hydrogen concentration in the steam oxidation stage were obtained during twenty successive redox reactions, which made them very attractive for the purpose of chemical looping partial oxidation of carbon fuel in real applications.