ABSTRACT
Temperature-programmed reduction combined with x-ray absorption fine-structure (XAFS) spectroscopy provided clear evidence that the doping of FischerTropsch synthesis catalysts with Cu and alkali (e.g., K) promotes the carburization rate relative to the undoped catalyst. Since XAFS provides information about the local atomic environment, it can be a powerful tool to aid in catalyst characterization. While XAFS should probably not be used exclusively to characterize the types of iron carbide present in catalysts, it may be, as this example shows, a useful complement to verify results from Mössbauer spectroscopy and other temperature-programmed methods. The EXAFS results suggest that either the Hägg or ε-carbides were formed during the reduction process over the cementite form. There appears to be a correlation between the α-value of the product distribution and the carburization rate.
