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Coal-based chemical looping gasification (CCLG) has been proposed as an emergent type of coal gasification technology that produces high-quality syngas by using lattice oxygen from oxygen carrier instead of molecular oxygen. In this paper, the Fe–Ni composite oxygen carrier was synthetized using sol-gel method and the gasification performance of the prepared sample was analyzed by a fixed-bed reactor. The results indicated that the Fe–Ni composite oxygen carrier presented a high carbon conversion of fuel and syngas selectivity during the CCLG process. Additionally, the cycle stability test showed that the carbon conversion of fuel and syngas selectivity did not change significantly with the increase of cyclic frequency. To further study the influence of volatiles released from coal on the gasification performance of oxygen carrier, the interactions between the oxygen carrier samples and char obtained at different pyrolysis temperatures were investigated by a fixed-bed reactor and TG-MS, respectively. The results suggested that the gas products (H 2 , CO, CO 2 and CH 4) yields of char-oxygen carrier were significantly lower than those of coal-oxygen carrier. Besides, the pyrolysis temperature for preparing char had a great effect on the carbon conversion of fuel and syngas selectivity due to the distinction of volatiles released from solid fuel. • Efficient Fe–Ni composite oxygen carrier was crafted via sol-gel method. • Fe–Ni composite oxygen carrier showed good performance with desirable reactivity and cyclic stability. • Interaction between oxygen carrier and volatiles released from coal was investigated. • Char gasification was demonstrated to be the rate determining step during the CCLG process. [ABSTRACT FROM AUTHOR]

A thermodynamic study on a toluene chemical looping reforming process with six metal oxides was conducted to evaluate the product distribution for selecting an appropriate oxygen carrier with thermodynamic favorability towards high syngas yield. The results show that a suitable operation temperature for most oxygen carriers is 900 °C considering syngas selectivity and solid C formation whether the toluene is fed alone or together with fuel gas. The syngas selectivity of all oxygen carriers decreases with the increasing equivalence ratio, but the decrease degrees are quite different due to their different thermodynamic natures. With the increasing amounts of H2 and CO, the syngas selectivity for various oxygen carriers correspondingly decreases. The addition of CO2 and H2O(g) benefits reducing the solid C formation, whereas the addition of CH4 leads to more solid C being produced. Under the simulated gasification gas atmosphere, a synergetic elimination of solid C and water–gas shift reactions are observed. In terms of syngas selectivity, Mn2O3 possesses the best performance, followed by CaFe2O4 and Fe2O3, but NiO and CuO exhibit the lowest performance. BaFe2O4 presents a high H2 selectivity but a very poor CO selectivity due to the formation of BaCO3, which has a high thermodynamic stability below 1200 °C. Nevertheless, Mn2O3 is more likely to form solid C than feeding toluene alone and has a lower melting point. Considering syngas selectivity, carbon deposit and melting point, CaFe2O4 exhibits the highest performance concerning the tar chemical looping. [ABSTRACT FROM AUTHOR]

Summary: This study proposes a novel methodology for controlling syngas production from high‐temperature CO2/steam co‐electrolysis. The co‐electrolysis of CO2/steam mixtures is one of the most promising methods to reduce CO2 emissions and mitigate climate change. CO2 and steam are reduced to produce synthetic gas (H2 and CO) through thermo‐electrochemical reactions occurring in a solid‐oxide‐cell fuel electrode. To make this technology viable, it is essential to improve electrochemical cell performance and obtain controllability of gas conversion and product gas selectivity. In this study, Fe infiltration to the Ni/YSZ fuel electrode and subsequent in situ alloying of Ni‐Fe is used to enhance the cell performance and syngas productivity. Impregnation of Fe‐oxide nanoparticles on the fuel electrode support of solid oxide cells and subsequent in situ alloying Ni‐Fe is obtained. Their homogeneous morphology and distribution are obtained by using an advanced infiltration technique. Results show that the Ni‐Fe/YSZ fuel electrode enhances CO selectivity and lowers an overvoltage imposed on the cell. This may result in syngas production with higher carbon contents and a higher co‐electrolysis system efficiency. In addition, its long‐term durability for 500‐hour operation is also evidenced with stable syngas production and negligible cell degradation. [ABSTRACT FROM AUTHOR]

To mitigate CO 2 emissions, its reduction by high-temperature electrolysis using solid oxide cells is extensively investigated, for which excessive steam supply is assumed. However, such condition may degrade its feasibility due to massive energy required for generating hot steam, implying the needs for lowering steam demand. In this study, high-temperature electrolysis of CO 2 - enriched mixtures by using fuel-electrode supported La 0.6 Sr 0.4 CoO 3 /YSZ/Ni-YSZ solid oxide cells is considered to satisfy such needs. The effect of internal and external steam supply on its electrochemical performance and gas productivity is elucidated. It is shown that the steam produced in-situ inside the fuel-electrode by a reverse water gas shift reaction may decrease significantly the electrochemical resistance of dry CO 2 -fed operations, attributed to self-sustaining positive thermo-electrochemical reaction loop. This mechanism is conspicuous at low current density, whereas it is no longer effective at high current density in which total reactant concentrations for electrolysis is critical. To overcome such limitations, a small amount of external steam supply to the CO 2 - enriched feed stream may be needed, but this lowers the CO 2 conversion and CO/H 2 selectivity. Based on these results, it is discussed that there can be minimum steam supply sufficient for guaranteeing both low electrochemical resistance and high gas productivity. [ABSTRACT FROM AUTHOR]

Efficient partial oxidation of methane at reduced reaction temperature was achieved by designing asymmetric Ni/SDC/LSCF membrane. Oxygen vacancies in the catalyst layer of asymmetric LSCF membrane can utilize the active oxygen species transported from air feed side to promote the selective syngas production. • Asymmetric membrane reactor achieved high syngas yield at reduced temperature. • Oxygen vacancies was introduced in catalyst layer to activate oxygen species. • Active lattice oxygen is proportional to oxygen vacancies and Sm 0.2 Ce 0.8 O 2−δ ratio. • The catalytic mechanism is suggested to be dominated by direct partial oxidation. Methane partial oxidation (POM) by a catalytic membrane reactor is a promising process by integration of oxygen separation and catalytic reaction to produce syngas, an important feedstock for downstream processes. However, high methane conversion and syngas yield require high temperature operation (>850 °C) due to dry/steam reforming involvement, which leads to high-energy consumption and poor catalyst stability. In this study, a novel asymmetric membrane reactor incorporated with a catalyst layer of enriched oxygen vacancy was designed for direct partial oxidation (DPO) of methane to syngas. A composite of Sm 0.2 Ce 0.8 O 2−δ (SDC)/γ–Al 2 O 3 supported Ni catalyst was coated on La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3−δ (LSCF) membrane for the reactor. It was found that activated oxygen species (O 2 −2 and O−2) from SDC surface favours syngas formation (86% CH 4 conversion and 92.5% CO selectivity) on the catalyst layer at 750 °C. The introduction of oxygen vacancies to the catalyst layer maintains the active oxygen species in catalysis and promotes DPO of methane over CH 4 combustion at reduced temperature. [ABSTRACT FROM AUTHOR]