Mass transfer usually affects the rate of chemical reactions in coal.The effect of internal diffusion on char gasification with CO2 in the temperature range from 1123 K to 1273 K was investigated via thermogravimetric analysis and assessment of char morphology features.The results revealed that the effect of internal diffusion on the initial reaction rate was more significant with an increase of particle size,due to the concentration gradient of the gasification agent within the solid particles.In the early stage of gasification,the generation of new micropores and the opening of closed pores led to an increase in specific surface area.As the reaction proceeded,the openings were gradually expanded and the specific surface area continued to increase.However,with further reaction,disappearance of edge pores,melting and collapse of the pore structure led to a decrease in specific surface area.The intrinsic activation energy and reaction order based on the nth-order model were 157.67 kJ· mol-1 and 0.36,respectively.Thus,temperature zones corresponding to chemical reaction and diffusion control were identified.Moreover,the calculated effectiveness factor provided a quantitative estimation of internal diffusion in the initial stage.