Chemical Looping Steam Reforming Research Articles

Interactions of Mg-Fe-Al-O oxygen carriers with rare earth dopants (Ce, Y, Sm, La, and Pr) in chemical looping steam reforming

Chemical looping steam reforming (CLSR) is a novel process for syngas and hydrogen co-production. In this work, rare earth metals (Ce, Y, Sm, La, and Pr) were doped to improve the reactivity and cyclic stability of the Fe-based oxygen carrier for CLSR. The cyclic tests indicate that the oxygen carrier doped with rare earth possesses a higher CH4 conversion rate, oxygen transport capacity, and hydrogen selectivity and yield. The crystal structure, surface morphology, and reactivity of the oxygen carrier were characterized by different analytical methods (e.g., XRD, H2-TPR, XPS, and SEM). The rare earth-doped oxygen carrier shows higher active site dispersion and smaller crystallite size owing to stronger metal-support interactions between the metallic Fe and the rare earth. XRD and SEM results revealed that the introduction of rare earth increases the oxygen transport capacity and oxygen vacancy concentration, promoting the reactivity of oxygen carriers. However, the rare earth doping reduces the CO purity, possibly because the high reactivity favors full CH4 oxidation. Among the prepared oxygen carriers, Fe10La exhibited the best performance and stability over cycles, with a high CH4 conversion rate (89.2%) and hydrogen purity (95 vol%).

Green hydrogen production from biomass – A thermodynamic assessment of the potential of conventional and advanced bio-oil steam reforming processes

Steam reforming of bio-oil derived from biomass pyrolysis is one of the most promising methods for the production of green hydrogen with minimal carbon footprint. In this context, this work investigates the thermodynamic potential of hydrogen production from bio-oil steam reforming. Four routes – conventional steam reforming (CSR) and three advanced reforming processes – sorption-enhanced steam reforming (SESR), chemical looping steam reforming (CLSR) and sorption-enhanced chemical looping steam reforming (SE-CLSR) - were modeled for this purpose. Bio-oil was modeled as a complex mixture of model compounds belonging to all major oxygenate families in order to have a closer resemblance with raw bio-oil. CaO was selected as the sorbent, while NiO was selected as oxygen carrier. Furthermore, the effect of process parameters such as steam to carbon, sorbent to carbon, oxygen carrier to carbon ratios, and reforming temperature was explored. H2 purity and yield along with energy demand, served as the parameters for comparing the performance of the four processes. SESR provided the highest H2 yield (0.216 kgH2 kgBio-oil−1) among all the processes under optimum conditions along with a purity greater than 99 %. CLSR, meanwhile, had the lowest H2 yield and purity (0.178 kgH2 kgBio-oil−1 and 64.6 %, respectively). The combined SE-CLSR process had H2 yield greater than both CSR and CLSR (0.197 kgH2 kgBio-oil−1) and a H2 purity greater than 99 %. High in-situ heat generation was noted in the reforming reactor for both SESR and SE-CLSR, pointing towards a good potential for auto-thermal operation. Overall, SE-CLSR process is a highly intensified process with substantially lower energy requirements than all the other processes. The results highlight that by combining CO2-sorption and chemical looping with traditional reforming, H2 can be obtained in higher yields and purity and lower energy consumption.

Hybrid solar-driven hydrogen generation by sorption enhanced–chemical looping and hydrocarbon reforming coupled with carbon capture and Rankine cycle

Hydrogen (H2) production from fossil fuels using Hydrocarbon Reforming Methods (HRM) accounts for nearly 95% of Global H2 production. Unlike hybrid Chemical Looping Steam Reforming (CL-SR) systems, the Integrated Solar-Driven Sorption Enhanced–Chemical Looping of Hydrocarbon Reforming (SE-CL-HR) utilises solar thermal energy from the Concentrating Solar Power (CSP) system to drive the endothermic decomposition of feedstocks. Furthermore, the simulated hybrid systems utilise recovered heat to generate electricity, reuse of by-product CO2 for more syngas production and finaly, CO2 capture by reaction of CaO to form CaCO3. This work focused on simulating hybrid CSP systems and SE-CL-HR plants with Heat Transfer Fluid (HTF) output temperatures between 750 and 1050 °C. In this study, System Advisor Model (SAM) and MATLAB software are used to develop the CSP system. While the CSP result saved in the MATLAB workspace gets exported to Simulink to feed SE-CL-SMR, SE-CL-POX and SE-CL-ATR Aspen plus models. The integrated system was fed with CH4 as the working fluid of the solar furnace. Stoichiometric and Gibbs free-energy minimisation were employed to investigate the effect of operating parameters. The output of the integrated system shows ≥9.5% exergy efficiency in comparison to conventional HRM. In addition, CO2 capture by CaO and high-pH water (Ca, Mg, Na+, O2, OH− and Cl−) to produce CaCO3, MgCO3 and other valuable products was also investigated in a process simulation. The research results revealed that for 8.1 tons/hr of CH4 and 277.1 tons/hrH2O (steam) flowrates, 62 tons/hr of H2 can be generated and 338.5 tons/hr of CO2 emission can be reused and captured by the adoption of these new innovative technologies.

Techno economic comparison of combustor integrated steam reforming and sorption enhanced chemical looping steam reforming of methanol

Methanol steam reforming (MSR) has gained significant attention for in-situ hydrogen (H2) production. To overcome the high energy requirement in the process, two modified methods such as combustor integrated steam reforming (CISR), and sorption enhanced chemical looping steam reforming (SE-CLSR) are widely used for the production of H2. In the present work, a techno-economic comparison of CISR and SE-CLSR models has been carried out using Aspen Plus V11to assess the economic viability of hydrogen generation by MSR process. SE-CLSR model is developed considering NiO as an oxygen transfer material (OTM). Simulations have been performed to observe a strong dependence of methanol conversion, hydrogen yield, CO selectivity with different operating conditions like temperature, steam to methanol (S/M) ratio, catalyst weight to methanol molar ratio. The sensitivity analysis of the considered models is performed to obtain the optimum operating conditions. The hydrogen production cost is estimated as 2.66 $/kg and 2.79 $/kg from CISR and SE-CLSR processes, respectively.

Sorption-enhanced chemical looping steam reforming of glycerol with CO2 in-situ capture and utilization

Hydrogen production from chemical looping steam reforming using an oxygen transport catalyst is definitely enhanced by CO2 in-situ capture, which shifts the chemical equilibrium and reduces the energy demands. The utilization of CO2 from this process as a reactant for chemicals and fuels could help to improve economic reasons and mitigate its impact on climate. In this study, we proposed a sorption-enhanced chemical looping steam reforming of glycerol to realize the synergetic capture and conversion of CO2 in one integrated chemical looping hydrogen production process. The process is characterized to usethe oxidized NiO/NiAl2O4 as a steam reforming catalyst, the reduced NiO/NiAl2O4 as a CO2-CH4 dry reforming catalyst, and the inexpensive dolomite as a CO2 sorbent. The surface carbon that would deactivate the catalyst is combusted by air after CO2-CH4 dry reforming and the Ni on the catalyst is re-oxidized. The coupling of these different processes of chemical looping steam reforming, CO2 in-situ capture, dolomite decomposition and CO2 in-situ utilization, results in simultaneous generation of high purity hydrogen and syngas. The results demonstrated that hydrogen of above 92.5% was one-step generated and CO2 was decreased to zero in the pre-CO2 breakthrough periods. The reduced NiO/NiAl2O4 catalysts favored the CO2-CH4 dry reforming at 850 °C. The syngas of H2-to-CO molar ratios of 0.8–1.1 through the conversion of CO2 from in-situ extraction of the absorbed CO2 dolomite, was produced. The NiO/Al2O4 with 15 wt% NiO gave the highest hydrogen and syngas yields, and maintained high performance for the proposed system. The catalysts and dolomite exhibited good stability with no obvious loss of activity in 10 cycles.

Recent Insights into the Production of Syngas and Hydrogen Using Chemical Looping-Steam Reforming (CL-SR)

Chemical looping-steam reforming (CL-SR) is a prospective technology for the simultaneous production of syngas and hydrogen (H2). The quality of syngas and hydrogen (H2) obtained from CL-SR process has garnered the interest of the scientific society. A recyclable oxygen storage material (oxygen carrier) is reacted through an alternating cycle of fuel (reduction step) and steam (oxidation step) at higher temperatures. Oxygen carrier (OC) plays a vital role in directing the path of the reaction in the CL-SR process. Hence, developing and selecting a proper OC is crucial. The current study intends to address recent breakthroughs in the development and performance of OCs subjected to different reacting fuel species such as methane (CL-SMR), CO2 (CL-HG), and liquid fuels. The performance of various classes of OCs such as metal oxide, mixed metal oxides, and perovskites toward conversion and lattice oxygen selectivity is investigated. The thermodynamic study and constraints related to the performance of OCs in CL-SR are discussed along with the economic evaluation of the CL-SR process and the conventional SMR process. Further, the theoretical approaches involved in determining the kinetics of the CL-SR process and kinetic models developed by the researchers are reviewed. Finally, the scientific barriers and the suggestions for optimized operation of the CL-SR process are listed.

Modulating lattice oxygen activity of Ca2Fe2O5 brownmillerite for the co-production of syngas and high purity hydrogen via chemical looping steam reforming of toluene

The chemical looping steam reforming (CLSR) of biomass tar enables the process intensification for the co-preparation of syngas and high purity hydrogen. The practical application of brownmillerite-structured Ca2Fe2O5 is hindered by activity-related issues such as low fuel conversion and oxygen transfer capacity. Here, the doping of heteroatoms, e.g. Ni induces structural changes to the brownmillerite lattice, transforming it from a Pnma phase to a Pcmn one, with increased distortion of the FeO6 octahedra. The structural changes lead to the upwards shifts of the O 2p band of oxygen carrier, and subsequently improved lattice oxygen activity as well as oxygen transfer capacity. The formation of oxygen vacancy is a rate determining step during CLSR, while the Ni-doped Ca2Fe2O5 reduces the energy of oxygen vacancy formation and energy barrier for lattice oxygen migration through the bulk. During CLSR, Ca2Ni0.25Fe1.75O5 lead to significant improvement in syngas productivity, hydrogen purity and fuel conversion.

Research progress on chemical looping reforming of macromolecular components of volatiles from biomass pyrolysis based on decoupling strategy

This paper focuses on the development of chemical-looping reforming of macromolecular organic compounds from biomass pyrolysis based on decoupling strategy, including glycerol, benzene, and toluene. Firstly, the influence characteristics of pyrolysis conditions on the distribution of volatile are analyzed. Pyrolysis temperature and heating rate are the two most important factors. Three technical routes to prepare hydrogen-rich syngas by chemical-looping reforming of typical macromolecular components in the volatile components of biomass pyrolysis were emphatically discussed, which include auto-thermal chemical-looping reforming (CLRa), chemical-looping steam reforming (CLSR), and chemical-looping dry reforming (CLDR). The types of oxygen carriers, reforming characteristics, and reaction mechanisms related to the above three routes were compared. In the future, chemical-looping reforming based on the decoupling strategy focuses on developing oxygen carriers with high lattice oxygen reserves, fast transmission rate and good anti-coke formation performance, and more efficient fluidized bed reactors. At the same time, density functional theory calculations and reaction experiments combined to reveal the reaction mechanism, integrate and optimize the system's energy flow and material flow.

Regulation of Oxygen Activity by Lattice Confinement over Ni Mg1−O Catalysts for Renewable Hydrogen Production

The chemical looping steam reforming (CLSR) of bioethanol is an energy-efficient and carbon-neutral approach of hydrogen production. This paper describes the use of a Ni x Mg 1− x O solid solution as the oxygen carrier (OC) in the CLSR of bioethanol. Due to the regulation effect of Mg 2+ in Ni x Mg 1− x O, a three-stage reaction mechanism of the CLSR process is proposed. The surface oxygen of Ni x Mg 1− x O initially causes complete oxidation of the ethanol. Subsequently, H 2 O and bulk oxygen confined by Mg 2+ react with ethanol to form CH 3 COO* followed by H 2 over partially reduced Ni x Mg 1− x O. Once the bulk oxygen is consumed, the ethanol steam reforming process is promoted by the metallic nickel in the stage III. As a result, Ni 0.4 Mg 0.6 O exhibits a high H 2 selectivity (4.72 mol H 2 per mole ethanol) with a low steam-to-carbon molar ratio of 1, and remains stable over 30 CLSR cycles. The design of this solid-solution OC provides a versatile strategy for manipulating the chemical looping process.

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.

Optimisation of syngas production from a novel two-step chemical looping reforming process using Fe-dolomite as oxygen carriers

The production of syngas from hydrogen carbon feedstocks such as natural gas and biomass is of high importance to the chemical industry. In conventional chemical looping steam reforming(CLSR), the composition of the syngas produced is limited by the chemical equilibrium of the water-gas-shift reaction. In this study, we demonstrate that a two-step chemical looping reforming (TS-CLR) process is capable of alleviating the equilibrium limit to produce syngas of higher CO and H2 contents. For example, the total mole fraction of H2 and CO in the syngas produced from the conventional CLSR of toluene at 900 °C is limited to below 89.4 vol% (dry basis), whereas TS-CLR could produce syngas with >94 vol% of CO and H2 under the same condintions. The TS-CLR process is best carried out in a bed of Fe-dolomite oxygen carriers with a Ca:Fe ratio of 1:1 (denoted as C1F1). Compared to the pure Ca2Fe2O5 and Fe2O3/Al2O3 oxygen carriers, the C1F1 affords improvements in syngas yield, carbon conversion and syngas purity. The superior performance of C1F1 is attributed to the promotion of the lattice oxygen activities of Ca2Fe2O5 by MgO, as well as its excellent phase reversibility over redox cycles.

Enhanced Fe2O3/Al2O3 Oxygen Carriers for Chemical Looping Steam Reforming of Methane with Different Mg Ratios

Fe2O3/Al2O3 oxygen carriers improved with Mg addition were used for the chemical looping steam reforming of methane (CLSR) in a lab-scale fluidized bed reactor. The oxygen carrier with a (Mg+Fe)/Al molar ratio of 0.5 exhibited the most promising reactivity and stability as CO selectivity, CH4 conversion, H2/CO, and H2 yield remained at 96%, 82%, around 2, and 0.75 mmol/g oxygen carrier, respectively, after the 15th cycle, and only the Mg–Fe–Al–O spinel appeared after 50 cycles. According to characterization, the Mg–Fe–Al interaction was the root cause of performance differences. With the increase of the Mg/Al ratio, the reacted oxygen carriers possessed a decreased Fe2+/Fe3+ and exhibited better lattice oxygen activity, but depressed the CH4 conversion and CO selectivity during the CH4 reduction stage. The oxygen carrier with low-lattice-oxygen activity followed the indirect mechanism with C as the intermediate product, leading to high CH4 conversion and CO selectivity.

Chemical looping steam reforming of glycerol for hydrogen production over NiO-Fe2O3/Al2O3 oxygen carriers.

Fe-based oxygen carriers (OCs) are widely used in chemical looping steam reforming (CLSR) due to excellent resistance to carbon buildup, low toxicity, and high activity. In this study, a type of nano NiO–Fe2O3/Al2O3 Fe-based OC that can easily be reduced by fuels and re-oxidized by air was developed for use in glycerol CLSR. It was synthesized by co-precipitation and impregnation. Based on the quadratic regression orthogonal model, a quadratic polynomial function was established to investigate the effects of temperature (T), water/carbon ratio (S/C), and loading (M) on hydrogen content (HL) and hydrogen selectivity (S). The OCs were characterized by XRD, XPS, SEM/EDX-mapping, TEM, and H2-TPR to determine their physicochemical properties. XPS shows the Fe phase highly interacted with the Al2O3 supporting matrix by forming Fe aluminates in NiO–Fe2O3/Al2O3. The S (85.33%) and HL (78.41%) were obtained under the optimal conditions T = 600 °C, S/C = 1.0 mol mol−1 and M = 0. A hydrogen content fluctuation within 4% was obtained under T = 700 °C, S/C = 1.0 mol mol−1, and M = 2.5%, which means the cycle stability is perfect because of the addition of Ni. This study provides a basis for the development of efficient oxygen carriers in the CLSR system.

Hydrogen Production from Chemical Looping Steam Reforming of Biomass Waste Cooking Oil

Hydrogen Production from Chemical Looping Steam Reforming of Biomass Waste Cooking Oil

Chemical looping steam reforming of ethanol without and with in-situ CO2 capture

Chemical looping steam reforming (CLSR) of ethanol using oxygen carriers (OCs) for hydrogen production has been considered a highly efficient technology. In this study, NiO/MgAl2O4 oxygen carriers (OCs) were employed for hydrogen production via CLSR with and without CaO sorbent for in-situ CO2 removal (sorption enhanced chemical looping steam reforming, SE-CLSR). To find optimal reaction conditions of the CLSR process, including reforming temperatures, the catalyst mass, and the NiO loadings on hydrogen production performances were studied. The results reveal that the optimal temperature of OCs for hydrogen production is 650 °C. In addition, 96% hydrogen selectivity and a 'dead time' (the reduced time of OCs) less than 1 minute is obtained with the 1 g 20NiO/MgAl2O4 catalysts. The superior catalytic activity of 20NiO/MgAl2O4 is due to the maximal quantity of NiO loadings providing the most Ni active surface centers. High purity hydrogen is successfully produced via CLSR coupling with CaO sorbent in-situ CO2 removal (SE-CLSR), and the breakthrough time of CaO is about 20 minutes under the condition that space velocity was 1.908 h−1. Stability CLSR experiments found that the hydrogen production and hydrogen selectivity decreased obviously from 207 mmol to 174 mmol and 95%–85% due to the inevitable OCs sintering and carbon deposition. Finally, stable hydrogen production with the purity of 89%∼87% and selectivity of 96%∼93% was obtained in the modified stability SE-CLSR experiments.

Hydrogen and syngas co-production by coupling of chemical looping water splitting and glycerol oxidation reforming using Ce–Ni modified Fe-based oxygen carriers

In this study, renewable hydrogen production was achieved by coupling of water splitting and glycerol oxidation reforming by chemical looping technology (CLWS-GOR) using the novel Ce–Ni modified Fe-based oxygen carriers (OCs). The OCs were developed by combining metal chelating sol-gel and isometric impregnation method, which exhibited anti-sintering characteristic and lattice oxygen migration ability in CLWS-GOR. The amount of hydrogen between 12.49 and 12.96 mmol in the steam stage was produced from all the OCs with different ratios of Fe, Ce and Ni. However, with the increase of Ce and Ni doping, the production of H2 and CO in the fuel stage increased, as well as the probability of carbon deposits released in the subsequent steam stage. The H2/CO ratio in syngas were easily adjusted by steam to carbon molar ratio (S/C) in chemical looping steam reforming (CLSR), but the effects of steam introducing led to gradual deterioration of OCs. The results proved the OCs prepared by the combination method has high activity and stability for renewable hydrogen production from coupling of CLWS-GOR.

Recent Progress in the Steam Reforming of Bio-Oil for Hydrogen Production: A Review of Operating Parameters, Catalytic Systems and Technological Innovations

The present review focuses on the production of renewable hydrogen through the catalytic steam reforming of bio-oil, the liquid product of the fast pyrolysis of biomass. Although in theory the process is capable of producing high yields of hydrogen, in practice, certain technological issues require radical improvements before its commercialization. Herein, we illustrate the fundamental knowledge behind the technology of the steam reforming of bio-oil and critically discuss the major factors influencing the reforming process such as the feedstock composition, the reactor design, the reaction temperature and pressure, the steam to carbon ratio and the hour space velocity. We also emphasize the latest research for the best suited reforming catalysts among the specific groups of noble metal, transition metal, bimetallic and perovskite type catalysts. The effect of the catalyst preparation method and the technological obstacle of catalytic deactivation due to coke deposition, metal sintering, metal oxidation and sulfur poisoning are addressed. Finally, various novel modified steam reforming techniques which are under development are discussed, such as the in-line two-stage pyrolysis and steam reforming, the sorption enhanced steam reforming (SESR) and the chemical looping steam reforming (CLSR). Moreover, we argue that while the majority of research studies examine hydrogen generation using different model compounds, much work must be done to optimally treat the raw or aqueous bio-oil mixtures for efficient practical use. Moreover, further research is also required on the reaction mechanisms and kinetics of the process, as these have not yet been fully understood.

The thermodynamic evaluation and process simulation of the chemical looping steam methane reforming of mixed iron oxides

Steam reforming chemical looping (CL-SMR) using mixed iron oxides has the potential as an alternative to the current partial oxidation (POX) and steam reforming (SMR) processes. In this study, the use of FeMoO4, Fe2ZnO4 and Fe2MnO4 as oxygen carriers (OC) under the CL-SMR reaction scheme was proposed to overcome the current disadvantages of methane POX and SMR processes. This research is aimed at finding potential iron-based metal oxides for the production of syngas, which can be regenerated under favorable conditions in steam, while producing H2. Thermodynamic evaluation and process simulation of the CL-SMR reaction scheme using mixed iron-oxides was performed. Results indicate that FeMoO4, Fe2ZnO4 and Fe2MnO4 generated syngas at 750 °C, 730 °C and 600 °C, respectively. However, FeMoO4 was not fully regenerated under favorable conditions, whereas Fe2ZnO4 and Fe2MnO4 were completely regenerated at 440 °C and 640 °C, respectively. Fe2MnO4 showed the most favorable operating conditions among the studied OC towards the production of syngas. Preliminary experimental studies involved the synthesis of Fe2MnO4 through a solid-state method using Fe2O3 and MnO as precursors, which was characterized via XRD, while its redox performance was evaluated in a TGA CH4–H2O redox cycle, with reduction using CH4 followed by the steam oxidation of OC. Results indicate that both reduction with methane and oxidation with water vapor using Fe2MnO4 present reasonable reduction–oxidation rates to be used in the CL-SMR reaction scheme, verifying the feasibility of the theoretical study performed in the present investigation.

Renewable hydrogen production from chemical looping steam reforming of biodiesel byproduct glycerol by mesoporous oxygen carriers

Abstract The selection of metal oxides and supports to improve catalytic activity and stability of oxygen carriers (OCs) is crucial for chemical looping steam reforming (CLSR) to hydrogen production. In this study, the Ni-based MCM-41 and SBA-15 OCs with and without CeO2 promoter were prepared by direct synthesis and impregnation methods. The BET, XRD, TEM, ICP-AES, H2-TPR and DSC-TGA were used to analyze the synthesized OCs. Hydrogen production by CLSR using biodiesel byproduct glycerol was studied in a fixed-bed reactor with fuel and air stages. The DSC-TGA experiments were carried out to determine the thermal decomposition of biodiesel byproduct glycerol and the results indicated the exothermic and/or endothermic reactions as a result of secondary reactions and, the main degradation with the mass loss of 85.5 wt% occurred in the stages of 150–500 °C. The mesoporous OCs presented high specific surface area, large pore volume, and uniform pore size. It was found that the NiO and CeO2 in the mesoporous OCs were first reduced by fuels and the reduced OCs was responsible of steam reforming and water gas shift (WGS) to hydrogen production, and hydrogen selectivity was up to 90% using CeNiO/SBA-15. The mesoporous OCs with Ce promoter greatly shortened ‘dead time’ (the reduce time of OCs), and effectively suppressed carbon deposited on OCs. High loading of NiO and CeO2 on SBA-15 improved oxygen transfer and achieved excellent cyclic stability. These findings provide the fundamental understanding and principle of design on the conventional Ni-based OCs with room for further developments in chemical looping process.

Layered Mg-Al spinel supported Ce-Fe-Zr-O oxygen carriers for chemical looping reforming

A series of layered Mg-Al spinel supported Ce-Fe-Zr-O oxygen carriers were prepared for co-production of syngas and pure hydrogen via chemical looping steam reforming (CLSR). The presence of magnesium-aluminum layered double oxides (MgAl-LDO) significantly increases the specific surface area of the mixed oxides, reduces the particle size of CeO2-based solid solution and promotes the dispersion of free Fe2O3. When reacting with methane, MgAl-LDO supported oxygen carrier shows much lower temperature for methane oxidation than the pure Ce-Fe-Zr-O sample, indicating enhanced low-temperature reactivity. Among different Ce-Fe-Zr-O(x)/MgAl-LDO samples, the Ce-Fe-Zr-O(40 wt%)/MgAl-LDO sample shows the best performance for the selective oxidation of methane to syngas and the H2 production by water splitting. After a long period of high temperature redox experiment, the Ce-Fe-Zr-O(40 wt%)/MgAl-LDO oxygen carrier still shows high activity for syngas generation. The comparison on the morphology of the fresh and cycled oxygen carriers indicates that the Mg-Al spinel support still forms a stable skeleton structure with high dispersion of active components on the surface after the long-term cycling, which contributes to excellent redox stability of the Ce-Fe-Zr-O(40 wt%)/MgAl-LDO oxygen carrier.