Xianming Cheng

Hydrogen and syngas production from two-step steam reforming of methane over CeO2-Fe2O3 oxygen carrier

Two-step steam reforming of methane (SRM) is a novel chemical looping process towards the production of pure hydrogen and syngas (synthesis gas), consisting of a syngas production step and a water-splitting step. Renewable energy can be used to drive this process for hydrogen production, especially solar energy. CeO2-Fe2O3 complex oxide oxygen carrier was prepared by the impregnation method and characterized by means of X-ray diffractometer (XRD), Raman spectroscopy (Raman) and hydrogen programmed reduction (H2-TPR). CH4 temperature programmed and isothermal reactions were adopted to test syngas production reactivity, and water splitting reaction was employed to investigate water-splitting activity. Moreover, two-step SRM performance was evaluated by a successive redox cycle. The results showed that CO-uncontaminated H2 and highly selective syngas (with H2/CO ratio close to 2) could be respectively obtained from two steps, and CeFeO3 formation was found in the first redox cycle and proved to be enhanced by the redox treatment. After 10 successive cycles, obvious CeFeO3 phase was detected, which may be responsible for favorable successive redox cycle performances.

Hydrogen and syngas production from two-step steam reforming of methane using CeO2 as oxygen carrier

Abstract CeO2 oxygen carrier was prepared by precipitation method and tested by two-step steam reforming of methane (SRM). Two-step SRM for hydrogen and syngas generation is investigated in a fixed-bed reactor. Methane is directly converted to syngas at a H2/CO ratio close to 2:1 at a high temperature (above 750 °C) by the lattice oxygen of CeO2; methane cracking is found when the reduction degree of CeO2 was above 5.0% at 850 °C in methane isothermal reaction. CeO2-δ obtained from methane isothermal reaction can split water to generate CO-free hydrogen and renew its lattice oxygen at 700 °C; simultaneously, deposited carbon is selectively oxidized to CO2 by steam following the reaction (C+2H2O→CO2+2H2). Slight deactivation in terms of amounts of desired products (syngas and hydrogen) is observed in ten repetitive two-step SRM process due to the carbon deposition on CeO2 surface as well as sintering of CeO2.

Preparation and characterization of Ce-Fe-Zr-O(x)/MgO complex oxides for selective oxidation of methane to synthesize gas

A series of Ce-Fe-Zr-O(x)/MgO (x denotes the mass fraction of Ce-Fe-Zr-O, x=10%, 15%, 20%, 25%, 30%) complex oxide oxygen carriers for selective oxidation of methane to synthesis gas were prepared by the co-precipitation method. The catalysts were characterized by means of X-ray diffraction (XRD) and H2-TPR. The XRD measurements showed that MgFeO4 particles were formed and Fe2O3 particles well dispersed on the oxygen carriers. The reactions between methane diluted by argon (10% CH4) and oxygen carriers were investigated. Suitable content of CeO2/Fe2O3/ZrO2 mixed oxides could promote the reaction between methane and oxygen carriers. There are mainly two kinds of oxygen of carriers: surface lattice oxygen which had higher activity but lower selectivity, and bulk lattice oxygen which had lower activity but higher selectivity. Among all the catalysts, Ce-Fe-Zr-O(20%)/MgO exhibited the best catalytic performance. The conversion of the methane was above 56%, and the selectivity of the H2 and CO were both above 93%, the ratio of H2/CO was stable and approached to 2 for a long time.

A yolk/shell strategy for designing hybrid phase change materials for heat management in catalytic reactions

Thermal energy storage technology is a promising option for implementing thermal management in advanced chemical processes, and phase change materials (PCMs) are recognized as the ideal thermal storage materials due to their high heat storage density and moderate temperature variation in charging/discharging processes. Herein, a yolk/shell strategy is firstly introduced to encapsulate PCMs with catalytic materials to fabricate a thermal storage functional catalyst. Chemical looping combustion technology, which couples endothermic and exothermic reactions, is chosen as the model process to observe the thermal storage behavior of such catalysts at a micro level. A novel method was proposed to prepare a yolk/shell Al@Al2O3 phase change composite, where the Al2O3 shell is obtained by the catalytic oxidation of surface layer of Al microspheres by O2 in the presence of Ni nanoparticles. After that, the Al@Al2O3 was coated with Fe2O3/Al2O3 to form an (Fe2O3/Al2O3)/(Al@Al2O3) thermal storage functional oxygen carrier. The Al@Al2O3 microspheres possess high latent heat (315 J g−1) and superior thermal conductivity (1.5–2.7 W (m K)−1). The voids between the yolk and the shell can serve as a buffering space for the volumetric changes of the Al core during the melting/freezing process, resulting in excellent charge/discharge stability. The heat released from the exothermic oxidation reaction can be efficiently absorbed by the PCM core to prevent thermal runaway. The thermal storage functional catalyst provides an intensive and practical approach for thermal management in complex chemical processes.