An evaluation of the reactivity of synthetic Fe-Ni oxygen carriers: CO oxidation, H2O reforming, and toluene cracking

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 approximate to Al2O3 > TiO2(anatase) > TiO2(rutile) > SiO2.

Automated summary

This study focused on evaluating the reactivity of NiFe2O4 in CO oxidation, H2O reforming, and toluene cracking, proposing a distributed activation energy model for the evaluation. The results showed that the sample synthesized by sol-gel method exhibited better reactive performance compared to other samples, indicating the potential applications of the DAEM in enhancing reactivity of oxygen carriers.