Gasification of metallurgical coke in CO2-CO-N2 with and without H2

•Coke gasification reaction with CO2 was studied with and without H2 using TGA.•Gasification rate with H2 is higher than that without H2 at lower temperatures.•The enhancing effect of H2 on gasification diminishes with temperature increase.•Gasification is controlled by the diffusion of CO2 as temperature increases.•Diffusion affects gasification at a lower temperature with H2 than without H2.