1. Research Institute of Special Chemicals, Taiyuan University of Technology, Taiyuan 030024, Shanxi, P. R. China
2. Shanxi Key Laboratory of Gas Energy Efficient and Clean Utilization, Taiyuan 030024, Shanxi, P. R. China
3. Key Laboratory of Coal Science and Technology of Ministry of Education and Shanxi Province, Taiyuan University of Technology, Taiyuan 030024, Shanxi, P. R. China