Dynamic x-ray diffraction studies of reduction and carbon monoxide hydrogenation over iron catalysts

The technique of dynamic x-ray diffraction (DXRD) was applied to studies of iron catalysts (supported and unsupported) during both reduction/oxidation and Fischer-Tropsch (FT) synthesis. In situ DXRD reduction of iron oxide supported on {dollar}gamma{dollar}-{dollar}Alsb2Osb3{dollar} {dollar}(alpha{dollar}-{dollar}Fesb2Osb3/Alsb2Osb3){dollar} showed that aluminum is unevenly incorporated into the matrix of supported iron oxide particles, leading to a form of metal-support interactions. This is manifested by iron oxide reduction rates which are much lower than for unsupported iron oxides.; Changes in bulk catalyst composition during FT catalysis over unsupported iron were correlated by in situ DXRD and it was found that the catalytic activity initially increased with increase in iron carbide formation, which is consistent with the "competition" mechanistic model. A catalyst deactivation was observed to be coincident with the {dollar}epsilonspprime{dollar}-{dollar}Fesb{lcub}2.2{rcub}Ctochi{dollar}-{dollar}Fesb{lcub}2.5{rcub}C{dollar} transformation. This and subsequent hydrogen etching experiments indicate that the carbon formed from this transformation may act as nucleation sites for subsequent carbon deposition.; Unreduced iron oxide catalysts were found to be significantly more stable than reduced iron catalysts due to direct formation of {dollar}chi{dollar}-{dollar}Fesb{lcub}2.5{rcub}C{dollar} from {dollar}Fesb3Osb4{dollar}. All of the FT results are consistent with the hypothesis that {dollar}chi{dollar}-{dollar}Fesb{lcub}2.5{rcub}C{dollar} is the active catalytic species which significantly deactivates due to the deposition of surface carbon. The deposition/polymerization rate of surface carbon can be significantly reduced if {dollar}epsilonspprime{dollar}-{dollar}Fesb{lcub}2.2{rcub}C{dollar} can be avoided during activation.