Different concentrations (0.1 and 1 M K+/Na+) of salt solutions (K2CO3, Na2CO3, NaOH and NaCl) were used to impregnate alkali in sawdust. After devolatilization, char samples were gasified at different temperatures (750-900 degrees C) under CO2 in a macro-thermogravimetric analyzer for gasification kinetics. Morphologically, three classes of chars could be identified. Chars experiencing the highest catalytic influence were in Class-2 (0.5 M K2CO3 and 1 M NaOH) with a swollen and molten surface. In contrast, Class-1 (wood char like) and Class-3 (with salt deposits) chars showed moderate and low catalytic effect on gasification reactivity respectively. It is believed to be related to char surface swelling and alkali salt used. At 850 degrees C or below, the reactivity increased linearly (Class-1 and Class-3 Char) with initial alkali content up to 2200 mmol alkali/kg of char (except for NaCI). The same reaction rate was maintained until 3600 mmol/kg of char of alkali loading (Class-2) and then decreased. However, no trend was observed at 900 degrees C due to drastic change in reactivity of the samples, probably due to alkali transformation. Among the salts, K2CO3 (0.5 M) was found to be the most suitable for catalytic gasification due to its high catalytic activity in combination with relatively low carbon leaching. (C) 2016 Elsevier Ltd. All rights reserved.