1. College of Chemistry and Chemical Engineering Shanxi Key Laboratory of Gas Energy Efficient and Clean Utilization Taiyuan University of Technology Taiyuan Shanxi 030024 P. R. China
2. Key Laboratory of Neutron Physics and Institute of Nuclear Physics and Chemistry China Academy of Engineering Physics Mianyang Sichuan 621999 P. R. China
3. Key Laboratory of Coal Science and Technology Ministry of Education and Shanxi Province Taiyuan University of Technology Taiyuan Shanxi 030024 P. R. China