An evaluation of the reactivity of synthetic Fe-Ni oxygen carriers: CO oxidation, H2O reforming, and toluene cracking
2021
Lin, Yan | Zhang, Zhen | Wang, Haitao | Fang, Shiwen | Huang, Zhen | Chen, Tianju | Wei, Guoqiang | Zhao, Kun | Zhao, Zengli | Wu, Jinhu | Fang, Yitian | Li, Haibin
NiFe₂O₄ is an ideal oxygen carrier for the chemical looping process. This study focused on the evaluation of NiFe₂O₄ reactivity in relation to CO oxidation, H₂O reforming and toluene (model tar) cracking. The NiFe₂O₄ was synthesized by the coprecipitation (CP), solid state (SS) and sol–gel (SG) methods for the TG and fixed bed experiments. We proposed a distributed activation energy model of the time integral, namely, DAEM-TI, for the evaluation of the reactivity of NiFe₂O₄ for CO oxidation (nonisothermal condition) and H₂O reforming (isothermal condition). The goodness of the model fitting agreed well with the experimental data for CO oxidation (nonisothermal condition) but was slightly worse for H₂O reforming (isothermal condition). The average activation energy, Eₘₑₐₙ, obtained by DAEM-TI was successfully used to determine the reactivity rank for different oxygen carriers. Eₘₑₐₙ analysis showed that the reactivity rank for CO oxidation was determined to be sample SG, sample SS and sample CP, and for H₂O reforming, the rank determined to be sample CP, sample SG and sample SS. These results agreed well with TG analysis, and this finding will inspire the applications of the DAEM. In general, the sample SG showed better reactive performance for CO oxidation, H₂O reforming and toluene cracking compared to the other samples. The inert support significantly increased the multiple redox cycle reactivity of NiFe₂O₄, and the improvement due to the inert support was ranked as follows: ZrO₂≈Al₂O₃ > TiO₂(anatase) > TiO₂(rutile) > SiO₂.
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