1. State Key Laboratory of High-Efficiency Coal Utilization and Green Chemical Engineering, Ningxia University, Yinchuan 750021, PR China
2. Institute of Clean Coal Technology, East China University of Science and Technology, Shanghai 200237, PR China
3. Department of Environmental Science and Technology, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama 226-8503, Japan