Sulfur released from five Chinese coals and an USA coal in hydrogen was correlated with the catalytic activity of an impregnated ferrous sulfate for hydrogenation of the coals. The hydrogenation was carried out at a high or ambient pressure. Sulfur released from the coals into the gas phase at the ambient pressure was monitored online with a flame photometric detector. The data indicate that the catalytic activity of the impregnated ferrous sulfate was promoted by the sulfur released from the coals. The promotion ability is proportional to the amount of sulfur released for the lower sulfur coals generally and levels out for the higher sulfur coals. The promotive effect of sodium sulfide on the activity of ferrous sulfate shows the similar behavior. Additional sulfur, no matter added or released, does not improve the catalytic activity further significantly for the higher sulfur coals. The results partially explain the difference in the catalytic activity of ferrous sulfate and effectiveness on added sulfur for different coals. (C) 2002 Elsevier Science Ltd. All rights reserved.