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Abstract: Fundamental pyrolysis/gasification characteristics of natural biomass and acid-washed biomass without alkali and alkaline earth metals (AAEM) were investigated by a thermogravimetric analyzer (TGA) and a fixed-bed reactor. In these experiments, six types of biomass were used and the contents of cellulose, lignin and AAEM species in the biomass were measured. It was observed that the characteristic of biomass pyrolysis and gasification was dependent on its components and AAEM species on the basis of TGA experiments. During biomass pyrolysis, the tar and gas yields increased with the growth of cellulose content, but the char yield decreased. There were two reactions indicating two major decomposition mechanisms. The first stage of decomposition showed rapid mass decrease due to the volatilization of cellulose, while the second stage became slow attributed to the lignin decomposition. The higher the cellulose content, the faster the pyrolysis rate. In contrast, the pyrolysis rate of biomass with higher lignin content became slower. In addition, the rises of cellulose content elevated the peak temperature of gasification and prolonged the gasification time. Meanwhile, the effect of AAEM species on gasification behavior was studied by comparing unwashed and acid-washed biomass. AAEM species increased the peak gasification value, whereas decreased initial gasification temperature. It revealed that the activity of biomass gasification was attributed to the interaction between AAEM–cellulose/lignin. [Copyright &y& Elsevier]