Research of hydrogen action during pre-sulfidation of direct coal liquefaction catalyst

A series of iron sulfide catalysts were prepared by pre-sulfidation at different temperatures and different hydrogen partial pressures, and their catalytic naphthalene hydrogenation activities were studied under 5 MPa 1% H₂S-H₂ atmosphere at 360 ℃. By means of XRD, MES, SEM-EDS, ICP and GC-MS, the effect of hydrogen on the pre-sulfidation process at different temperatures was studied. The results show that the introduction of hydrogen during the pre-sulfidation process facilitates the transfer of sulfur, thereby promoting the sulfidation. The effect of hydrogen is different at different pre-sulfidation temperatures. When pre-sulfidation at 50 ℃, the introduction of hydrogen can be beneficial to the transfer of sulfur, which increases the catalytic activity, but a lot of elemental Fe and elemental S can still be observed at this temperature; when pre-sulfidation at 150 ℃, the catalytic activity is the best. The content of zero-valent Fe decreases and no pure S is observed. With the increase of hydrogen partial pressure, the hydrogenation conversion of naphthalene increases from 60.6% to 69.1%. When pre-sulfidation at 300 ℃, the catalytic activity decreases with the introduction of hydrogen. Hydrogen reduces the sulfur on the catalyst surface to low valence state and crystalline Fe₃O₄ is observed inside the catalyst particles, which is not conducive to the transfer of sulfur.