New process for catalytic liquefaction of coal using dispersed MoS₂ catalyst generated in situ with added H₂O

We have found that adding a proper amount of water can dramatically improve conversion of a sub-bituminous coal in solvent-free liquefaction under at 350 °C using ammonium tetrathiomolybdate (ATTM) as precursor to dispersed MoS₂ catalyst H₂ pressure. However, adding water to catalytic reactions at 400 °C decreased coal conversion, although water addition to the non-catalytic runs was slightly beneficial at this temperature. We further examined the effect of water in solvent-mediated runs in addition to `dry' tests and explored a temperature-programmed liquefaction (TPL) procedure to take advantage of the synergetic effect between water and dispersed Mo catalyst precursor at low temperatures for more efficient coal conversion. The TPL using ATTM with added water at 350 °C, followed by water removal and subsequent reaction at 400 °C gave good coal conversion and oil yield. Model reactions of dinaphthyl ether (DNE) were also carried out to clarify the effect of water. Addition of water to ATTM substantially enhanced DNE conversion at 350 °C. The combination of data from one-step and two-step tests of DNE and coal at 350-400 °C revealed that water results in highly active MoS₂ catalyst in situ generated at 350 °C, but water does not promote the catalytic function or reaction once an active catalyst is generated. Using ATTM coupled with water addition and removal and temperature-programming may be an effective strategy for developing a better coal conversion process using dispersed catalysts.