Abstract Investigation of a series of chars prepared by rapid pyrolysis of cellulose in the temperature range of 400–800°C has shown that they have a high chemisorptive affinity for oxygen. Maximum chemisorption occured on chars prepared at a HTT of 550°C. The Elovich equation was used to describe the kinetics of the process. The extent of chemisorption decreased with increasing HTT of the chars, although the surface area of the chars stayed approximately constant; indicating the presence of less reactive areas on the surface of chars formed at higher temperatures. As chemisorption progressed there was a corresponding increase in the intensity of several IR absorption bands, which were attributed to the formation of stable oxygen-containing functional groups. The chemisorption process, preceded by physical adsorption, does not influence the gasification reaction. The presence of impurities from pre-pyrolysis doping of cellulose could promote or inhibit the rate of gasification but had negligible effect on the initial rate of chemisorption. The role of these two processes in char combustion was discussed in the light of known concepts for the carbon-oxygen reaction.