Catalytic mechanism of ion-exchanging alkali and alkaline earth metallic species on biochar reactivity during CO2/H2O gasification

To understand the detailed catalytic mechanism of ion-exchanging AAEM species on biochar structure and its specific reactivity during CO2/H2O gasification, the experiments were carried out in a laboratory fixed-bed reactor at 800 degrees C, with two kinds of AAEM-loading methods. The migration and precipitation characteristics of AAEM species was evaluated by ICP-AES, while the transformation of biochar structures were analyzed by FTIR and Raman. The specific reactivity of H2O/CO2 gasification biochar was determined by TGA analysis in Air at 370 degrees C. The results show that the stronger catalytic properties of K and Ca species in H2O atmosphere are obtained than that in CO2. The effect of K is mainly on the formation of O-containing functional groups (e.g. alcohol/phenolic-OH, aldehyde/ester C = O and carboxylic -COO- groups) and the transformation from small ring systems to larger ones, while the catalytic effect of Ca is only to increase the proportion of large aromatic ring structures (>= 6 fused benzene rings). The biochar-CO2 reaction took place mainly at the gas-solid interface of biochar, while biochar-H2O one existed throughout the biochar particle. A better distribution of active sites (i.e. surface K/Ca species and O-containing groups) on biochar surface would result in the high specific reactivity of biochar during gasification.