Structural analysis of iron and manganese species in iron- and manganese-promoted sulfated zirconia

The structural analyses of Fe, Mn-SO42-/ZrO2 (FMSZ), Fe-SO42-/ZrO2 (FSZ), Mn-SO42-/ZrO2 (MSZ), and Fe-Mn/ZrO2 (FMZ) were carried out by means of XAFS, XRD, and Raman spectroscopy. Local structure around Fe and Mn of each catalyst, which were at a working state for n-butane isomerization and in vacuo, were studied by in situ XAFS. The valence of the Fe atom of all the catalysts was invariantly trivalent. Coordination environment around Fe of all the catalysts was quite similar to each other. Fe atoms are present inside the bulk phase of ZrO2, the system of which forms interstitial-type solid solution and located at the center of distorted oxygen octahedra. Reaction gas does not directly make contact with Fe atoms because the introduction of reaction gas did not cause any change of coordination environment and the valence. The Mn species on FMSZ and MSZ were present as MnSO4, and their coordination environment was reversibly affected by exposure to n-butane. Without sulfate ions, Mn species are present on the catalyst as alpha-Mn2O3.