In order to understand the transformation mechanisms of iron-sulfur catalys
t systems to pyrrhotite, the iron catalysts (gamma-FeOOH, alpha-FeOOH, Fe(C
O)(5) and Fe-3(CO)(12)) and sulfur compounds (S and H2S) were heat-treated
at 150-420 degrees C with or without an activated carbon, and then subjecte
d to XRD and XPS analyses. Pyrrhotite (Fe1-xS) was the major phase above 20
0 degrees C in the XRD profiles of all iron-sulfur catalyst systems. Howeve
r, the formation of pyrite (FeS2) from gamma-FeOOH and gamma-FeOOH on the c
atalyst surface was observed at 150-325 degrees C by XPS analyses. This res
ult seems to indicate that active species (Fe1-xS) would be transformed thr
ough FeS2 as an intermediate, but iron carbonyl complexes were directly tra
nsformed into pyrrhotite without the formation of FeS2. (C) 2000 Elsevier S
cience Ltd. All rights reserved.