The CH4-CO2 reforming process is of great importance for current chemical industry, since it could utilize the two cheapest carbon-containing compounds with production of value-added syngas. However, sintering and carbon deposition of catalysts greatly hampers the industrial implementation of this route. Chemical looping CH4-CO2 reforming provides a novel route to directly produce syngas with a H2/CO ratio of ~ 2.0 from methane in combined with CO2 utilization via the transport of oxygen carrier (OC), which emerges as an attractive technology for syngas production, enabling the use of low-cost transition metal oxides, controllable carbon deposition via the incomplete reduction of OC, and resulting in the inherently H2/CO ratio of ~2.0 by avoiding mixed CH4/CO2 streams. The chemical looping CH4-CO2 reforming performance is highly dependent on the microstructure of OC. The relationship between the microstructure of oxygen carrier and reactivity is of great value for the rational designing of OC.
A team of researchers led by Professor Xiaodong Wang and Professor Tao Zhang (http://www.taozhang.dicp.ac.cn/eng/index_eng.php) at Dalian Institute of Chemical Physics (DICP), Chinese Academy of Sciences, P.R. China firstly used Fe-substituted La-hexaaluminate, which is usually regarded as high-temperature catalyst in combustion and aerospace fields, as OC in the chemical looping CH4-CO2 reforming. It was found that Fe-substituted La-hexaaluminate exhibited good reactivity and stability in the successive CH4/CO2 redox cycles. The La-hexaaluminate structure was still preserved even during CH4 reduction with the synthesis gas generation. This is very different from many OCs reported at the present time, wherein they usually lost their structure during reduction. They found that sole CO2 oxidant more favored improving synthesis gas selectivity than using O2/air through the selective regeneration for O5-Fe3+(Tr) and O4-Fe3+(Th) related to synthesis gas production, which offers an attractive opportunity for CO2 utilization. Furthermore, they studied the structural evolution of Fe-substituted La-hexaaluminate (LFA-t, t = 900-1200 oC) as thermal treatment and ten periodic CH4/CO2 redox cycles, and correlated to their reactivity and stability for syngas production. Their work is now published in the research journal, AIChE Journal and International Journal of Hydrogen Energy.
The optimized hexaaluminate materials with excellent redox property and high temperature stability developed by Professor Xiaodong Wang could be considered as one of promising chemical looping CH4-CO2 reforming OCs.
 Yanyan Zhu, Weiwei Liu, Xueyan Sun, Xiaoxun Ma, Yu Kang, Xiaodong Wang*, Junhu Wang, La-hexaaluminate for synthesis gas generation by chemical looping partial oxidation of methane using CO2 as sole oxidant. AIChE J., 2018, 64(2): 550-563.
 Yanyan Zhu, Xueyan Sun, Weiwei Liu, Peng Xue, Ming Tian, Xiaodong Wang*, Xiaoxun Ma, Tao Zhang. Microstructure and reactivity evolution of La-Fe-Al oxygen carrier for syngas production via chemical looping CH4-CO2 reforming. Int. J. Hydrogen Energy, 2017,42:30509-30524.
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