The catalytic effect of iron oxide phases on the conversion of cellulose-derived chars in diluted O2 and CO2

The conversion of biomass-derived char is substantially influenced by its metal content. One of the main catalytically active metallic elements in biomass is Fe, which occurs in various mineral forms. For the implementation of catalytic effects into char conversion models, investigations on the role of mineral type and loading are required. In this work, the catalytic effect of an Fe sulfate loading series on the oxidation and gasification of an inherently mineral-free cellulose-derived char was analysed. Characterisation focused on the Fe phases present in the char identifying the transformation from FeSO4 to γ-Fe2O3 during doping, and further to ε-Fe2O3 and α-Fe2O3 upon char oxidation as well as to FeO and γ-Fe upon char gasification. Very high loading-dependent activities of ε-Fe2O3 and FeO were quantified by kinetic modelling. These iron oxides strongly catalyse char conversion, lowering the activation energy by up to 14% and 18%, respectively, relative to the mineral-free char.