Transformation of iron catalysts (α-FeOOH, γ-FeOOH, ferrihydrite, natural pyrite and limonite) to pyrrhotite (Fe_(1-x)S) was investigated through the sulfidation tests with elemental sulfur in relation to the catalytic activity for direct liquefaction of brown coal. The crystallite size of Fe_(1-x)S from γ-FeOOH was smaller than that from other iron based catalysts, and Fe_(1-x)S formed at lower temperature had a relatively high surface area and sulfur-rich Fe_(1-x)S structure. It was found that γ-FeOOH had a good catalytic activity for hydrogen transfer to radical fragments in initial stage of coal liquefaction and H_2S partial pressure in a reaction system was important to suppress the deactivation of recycled catalyst.
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