The effort for increasing syngas production and reducing soot and CO2 emissions from coal combustion is important for cleaner and more efficient use of coal for energy production. The primary reactions of coal volatiles for soot formation mechanism were numerically investigated under pyrolysis (thermal decomposition), partial oxidation (O-2 gasification) and O-2/CO2 gasification conditions. Soot formation was modeled in a plug flow reactor (PFR) with a detailed reaction mechanism containing 276 species, 2158 conventional gas phase reactions and 1635 surface phase reactions. The reaction temperature and pressure were maintained in the range 1273-1873 K and 0.1-2 MPa, respectively. The effect of temperature on product concentrations appeared more significant compared with pressure effect. In the viewpoint of special attention regarding O-2/CO2 blown gasification, the effect of O-2/CO2 input on the production of major combustion species was investigated. The O-2 input became important in reducing PAHs/soot at low temperature. However, if the gas mixture input had a high CO2 concentration, higher temperature and pressure provided in eliminated PAHs/soot and increased CO. (C) 2011 Elsevier Ltd. All rights reserved.