1. State Key Laboratory of Coal ConversionInstitute of Coal ChemistryChinese Academy of Sciences Taiyuan 030001 P. R. China
2. Center of Materials Science and Optoelectronics EngineeringUniversity of Chinese Academy of Sciences Beijing 100049 P. R. China
3. Institute of Materials EngineeringUniversity of Siegen Siegen 57076 Germany
4. School of Petrochemical EngineeringChangzhou University Changzhou 213164 P. R. China