1. Graduate School of Energy Science and Technology, Chungnam National Univ., 99 Daehak-ro, Yusung-gu, Daejeon 305-764, Korea.
2. Dept. of Applied Chemistry and Biological Engineering, Chungnam National Univ., 99 Daehak-ro, Yusung-gu, Daejeon 305-764, Korea.
3. Clean Coal Center, Korea Institute of Energy Research, 152 Gajeong-ro, Yuseong-gu, Deajeon 305-343, Korea.
4. Professor, Graduate School of Energy Science and Technology, Chungnam National Univ., 99 Daehak-ro, Yusung-gu, Daejeon 305-764, Korea (corresponding author).