This chapter reviews the unusual and strong promoting effect of water on low-severity catalytic liquefaction of Wyodak sub-bituminous coal. The primary drying effect on coal conversion at 350°C is due to water removal rather than physicochemical changes within coal structure caused by drying. Prompted by this observation, the effect of water on catalytic run finds that water can have strong promoting effect on catalytic coal liquefaction with a dispersed molybdenum (Mo) sulfide catalyst at 350°C. The chapter examines the water effect using dispersed Mo catalysts generated in situ from water-soluble precursor, ammonium tetrathiomolybdate (ATTM), and an oil-soluble precursor. It describes new opportunities for developing low-severity catalytic processes for coal liquefaction that uses dispersed Mo sulfide catalysts from either water-soluble or oil-soluble precursor; adding a proper amount of water dramatically improve coal conversion at temperatures lower than the conventional processes.
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