Iron-based catalysts have been one of the most active fields in coal direct liquefaction technology due to their advantages of a vast source of raw materials

low synthesis cost

and high catalytic activities. In this study

five oil-soluble iron-based catalysts with different carbon chain lengths were synthesized by reacting a series of fatty acid sodium salts with trivalent iron salts as raw materials. The catalyst precursors synthesized were structurally characterized using inductively coupled plasma emission spectroscopy

Fourier transform infrared spectroscopy

and high-resolution mass spectrometry. In the presulfurization and activity evaluation experiments of coal direct liquefaction carried out in an autoclave

it was found by X-ray diffraction transmission electron microscopy and X-ray photoelectron spectrometry that the iron oleate catalysts formed highly catalytic Fe1−xS phases during the sulfurization process

with average particle sizes of ∼200–300 nm and uniform distribution. The results of catalyst activity evaluation showed that under the same reaction conditions (temperature 455°C

reaction pressure 19 MPa

residence time 60 min) and

with the same addition amount of m(Fe)/m(dry coal) = 1%

the iron oleate catalyst exhibited excellent catalytic performance

with a coal conversion of 89.45% and an extraction oil yield of 64.04%

which was significantly better than that of other oil-soluble iron-based catalysts. It is worth noting that the iron oleate catalyst can achieve comparable catalytic performance at a lower addition amount (m(Fe)/m(dry coal) = 0.5 wt%) compared with the ultrafine hydrated iron oxide (FeOOH) catalyst

which requires an addition amount of m(Fe)/m(dry coal) = 1 wt%. This not only reduces the cost of catalyst usage but also simplifies the subsequent dehydration and drying processes. The findings of this study hold significant importance for the development of new

high-efficiency catalysts for coal direct liquefaction and offer a theoretical foundation and technical support for the industrial application of coal-to-liquid technology.