Catalytic reforming of volatiles from co-pyrolysis of lignite blended with corn straw over three iron ores: Effect of iron ore types on the product distribution, carbon-deposited iron ore reactivity and its mechanism

Natural iron ore is widely used as a catalytic cracking material in the reforming and upgrading of co-pyrolysis volatiles, where its surface carbon deposition structure can strongly impact the reduction reaction process. Here, the availability of three natural iron ores for the catalytic reforming of volatiles from the co-pyrolysis of lignite and corn straw (CPLC) was investigated to study the influence of ore type and reaction temperature on product yield, tar composition as well as phase transformation of iron ore. Goethite exhibited a relatively good catalytic effect on the cracking of heavy components, followed by specularite and hematite. Almost all of the Fe2O3 peaks in the carbon-deposited iron ore disappeared, and Fe3O4 peaks appeared instead. Additionally, the most energetically favourable pore size of carbon deposition ranged from 2 similar to 4 nm, as determined by comparing the structural changes of iron ore before and after the reaction. The deposited carbon did not completely fill in the nanocracks and voids due to the presence of tar, which caused clogging on the surface of the iron ores. The results indicate that in three carbon-deposited iron ores, the content of C-O and C=O species decreased in the order goethite > specularite > hematite. Since carbon deposits contain more oxygen-containing functional groups (OCFGs) that are similar to a magnet that attracts carbon deposits, this can promote the continuous supply of reductants for iron ore reduction, and thus, carbon-deposited iron ore can be used to store energy, thereby reducing the consumption of additional reducing agent.