Chemical-looping combustion (CLC) and chemical-looping gasification (CLG) are innovative technologies for clean and efficient conversion of carbonaceous feedstock into power, fuels and value-added chemicals through cyclic redox reactions. Metal oxide materials play a key role in the chemical looping redox processes.  Low cost, multiple phases and environmental friendly nature of iron oxide leads to the commercial viability of chemical looping technology. However, the moderate reactivity and recyclability of iron oxide, due to, high reaction activation energy and low ionic conductivity, largely hinders the successful commercialization of chemical looping process. Aliovalent dopants can increase the redox reactivity of iron oxide by not only providing active sites for carbonaceous feedstock conversion , but also creating oxygen vacancies for improved ionic conductivity. In this work, we compare the impact and reaction mechanism of aliovalent Ni-, Co- and Cu- modified iron oxides that undergo cyclic redox reactions using methane reforming as an example. Density functional theory (DFT) predicts that modified surface and internal configuration with Ni-, Co- or Cu-doped iron oxides can significantly decrease the reaction activation energy of methane dissociation. In addition, the surface modification can lower the formation energy of oxygen vacancy, and these dopant-induced oxygen vacancies are beneficial for lattice oxygen diffusion. Experimental results confirm the universally reactivity increase in aliovalent dopant modified oxygen carriers in chemical looping operating temperature windows compared to undoped iron oxide. A detailed morphological and structural characterization was performed on both surface and internal of the oxide particles to investigate the similarity and differences among the above-mentioned dopants. The understanding of methane conversion mechanism has provided us the guideline to particle design and has successfully led to the production of commercially viable oxygen carriers.<br/>

Aliovalent dopant-induced reactivity and recyclability enhancement in iron based  oxygen carrier for chemical looping applications

255th National Meeting (2018)

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