The relationship between the microstructures and catalytic behaviors of iron–oxygen precursors during direct coal liquefaction

Abstract A series of both unsupported and coal-supported iron–oxygen compounds with gradual changes in microstructure were synthesized by a precipitation-oxidation process at 20 to 70 °C. The relationship between the microstructures and catalytic activities of these precursors during direct coal liquefaction was studied. The results show that the microstructure could be controlled through adjusting the synthesis temperature during the precipitation-oxidation procedure, and that compounds synthesized at lower temperatures exhibit higher catalytic activity. As a result of their higher proportions of γ-FeOOH or α-FeOOH crystalline phases, the unsupported iron–oxygen compounds synthesized at 20–30 °C, which also had high specific surface areas and moisture levels, generate oil yields 4.5%–4.6% higher than those obtained with precursors synthesized at 70 °C. It was also determined that higher oil yields were obtained when the catalytically-active phase formed by the precursors during liquefaction (pyrrhotite, Fe 1− x S) had smaller crystallites. Feed coal added as a carrier was found to efficiently disperse the active precursors, which in turn significantly improved the catalytic activity during coal liquefaction.