Promoted catalysis of calcium on the hydrogasification reactivity of iron-loaded subbituminous coal

•Ca facilitated the dispersion of metallic Fe in coal char.•Ca and Si formed Ca3SiO5 to promote the reduction of iron oxide to iron metal.•Ca species existing as CaO(COO) could release CO2 which react with Fe3C.•Fe-(O)-C triggered hydrogasification and maintained the high dispersion of Fe.