Steam reforming of tar derived from lignin over pompom-like potassium-promoted iron-based catalysts formed on calcined scallop shell

•Pompom-like K-promoted iron-based catalysts were prepared on calcined shell.•A mechanism for the formation of pompom-like microspheres was proposed.•An excellent catalytic activity were exhibited for the steam reforming of tar. In order to understand the improvement effect of potassium (K) on the catalytic activity of iron-loaded calcined scallop shell (CS) for the steam reforming tar derived from biomass, various K precursors were applied for the catalyst preparation. It is found that pompom-like iron-based particles with a mesoporous structure were easily formed on the surface of calcined scallop shell (CS) when K2CO3 was used as K precursor while no such kind of microsphere was formed when other kinds of K precursors such as KOH and KNO3 were applied. The optimum K-loading amount for the preparation of this catalyst was investigated. Based on the experimental results obtained, a mechanism for the formation of these microspheres was proposed. This pompom-like potassium-promoted iron-based catalyst showed a better catalytic activity and reusability for the steam reforming of tar derived from lignin.