Synthesis of FeOOH Polymorphs by Room Temperature Solid-State Chemical Reaction: Effect on the Selective Cracking of Aromatic Hydrocarbons with C-O Bridge Bonds.

FeOOH polymorphs are valued in industrial catalysis for selective hydrogenation of organics in coal to high - value aromatics, yet the factors behind their differing efficiencies are still unclear. In this work, the synthesis of FeOOH nanopolymorphs with sizes from 80 to 300 nm was achieved through a simple, efficient, and environmentally friendly room temperature solid-phase chemical reaction. FeOOH polymorphs demonstrate different iron oxidation states and abundant surface hydroxyls. Among them, δ-FeOOH, with its lower iron oxidation state and rich surface hydroxyls, enhances hydrogen adsorption and lowers hydrogen activation energy through hydrogen bonding. Notably, δ-FeOOH achieved the complete conversion of benzyl phenyl ether, a typical α-O-4 linkage model compound in coal at 270 °C and 20 bar H2 for 2 h. This study provides valuable insights into the intricate relationship between FeOOH polymorphs and catalytic performance, contributing to the sustainable development of FeOOH-based hydrogenation catalysts.