Highly active catalysts from inexpensive raw materials for coal gasification

The present review article focuses on novel methods of converting inexpensive raw materials to active catalysts for low-temperature coal gasification, which can produce clean fuels and valuable feedstock with high thermal efficiency. Precipitation methods using NH3, urea, and Ca(OH)(2) make it possible to prepare active, Cl-free iron catalysts on brown coals from an aqueous solution of FeCl3 as the major component in acid wastes. The use of Ca(OH)(2) provides the mast active iron, which achieves complete gasification within 60 min in a thermogravimetric nm at 973 K. Ca(OH)(2) and CaCO3 are other promising catalyst sources. Ca(OH)(2) promotes the steam gasification of many coals with different ranks at 973 K when kneaded with them in water. The calcium shows a larger catalytic effect for low-rank coals with higher contents of oxygen-functional groups as ion-exchangeable sites. CaCO3, as a raw material of Ca(OH)(2), reacts with COOH groups to form ion-exchanged Ca and CO2 when mixed with brown coals in water. Ion-exchange reactions proceed more readily with aragonite naturally present in seashells than with calcite from limestone. The exchanged calcium shows higher catalytic activity than the precipitated iron and provides at the largest 40-60-fold rate enhancement during steam gasification at 973 K. Catalysis of coal gasification by the iron and calcium is discussed in terms of catalyst dispersion, reactive sites, and sulfur poisoning. (C) 1997 Elsevier Science B.V.