Effect of catalyst precursors on coal reactivity in catalytic hydropyrolysis

The use of dispersed sulphided molybdenum and hydrous titanium oxide (HTO) catalysts enable tar yields in excess of 60% daf coal to be obtained for bituminous coals in fixed-bed hydropyrolysis using relatively mild conditions. However, it was found that a key difference between hydropyrolysis and batchwise hydrogenation is that the active form of the catalyst must be formed at a lower temperature in hydropyrolysis in order to be effective because of the much higher heating rates used. Thus, ammonium dioxydithiomolybdate which decomposes to form a sulphided Mo compound below 250 °C and Pd-exchanged HTO, where the Pd is reduced below 100 °C, have been found to be particularly effective (∼0.2%. Mo required to achieve maximum conversion). Molybdenum naphthenates and iron sulphides are much less effective in hydropyrolysis than in direct liquefaction because the active phases (MoS 2 and pyrrhotite) are not appreciably formed below about 400 °C. Preliminary results indicate that low concentrations of Mo (about 0.02%) have considerable activity when ion-exchanged onto HTO-coated coals.