1. School of Energy and Power engineering North University of China Taiyuan 030051 Shanxi P. R. China
2. State Key Laboratory of Coal Conversion Institute of Coal Chemistry Chinese Academy of Sciences Taiyuan 030001 P.R. China
3. University of Chinese Academy of Sciences Beijing 100049 P.R. China
4. School of Materials and Chemistry University of Shanghai for Science and Technology 516 Jungong Road Shanghai 200093 P.R. China