In order to obtain fundamental information on pressurized catalytic gasification of carbonaceous materials, four coal chars loaded with alkaline earth carbon-ates were gasified in a thermobalance at 1, 5 and 25atm of CO2. The measured catalytic activity of the additives was discussed in terms of their chemical states and reactions of them with mineral matters in the coal chars under the gasification conditions checked by X-ray diffraction.
All the carbonates except magnesium salt raised the gasification reactivity of the coal chars remarkably, and the catalytic activity at high pressures was almost independent of the coal char species. However, under 1 atm of CO2, the catalytic activities were very small with chars of high ash content. This dependence of the catalytic activity on pressure of CO2 is explained by the results from X-ray diffraction, i.e., alkaline earth carbonates become stable under higher pressure of CO2 but under 1 atm they reacted with silica and alumina components to form silicates and aluminosilicates, and lose the catalytic activity.