Scientists from DOE’s National Energy Technology Laboratory (NETL) and Berkeley Lab used scanning tunneling microscopy (STM) and ambient-pressure x-ray photoelectron spectroscopy (AP-XPS) at ALS  Beamline 9.3.2 to examine nanocrystals and continuous thin films of α-Fe₂O₃ grown on Au(111), and to gain insight into the structure-property relation of a material under realistic conditions. The nanocrystalline α-Fe₂O₃/Au(111) system has significant amounts of edge and interfacial sites, while the density of these structural features are low or nonexistent in the continuous films of α-Fe₂O₃ on Au(111). The distinctive morphologies of the two systems result in different reactivity when exposed to a high pressure of carbon monoxide (CO) gas:

• The nanocrystalline α-Fe₂O₃/Au(111) system is capable of adsorbing CO at room temperature and then converting CO with adsorbed OH to formate at elevated temperatures, a key step for the low temperature water gas shift reaction.
• The continuous films of α-Fe₂O₃ on Au(111) are inert under the same conditions due to the absence of edge and interfacial sites.

The comparative studies clearly establish a relationship between structure and activity and demonstrate the crucial roles of edges and interfaces in catalytic reactions.

A detailed characterization of an individual α-Fe₂O₃ particle grown on Au(111), showing stepped edges and interfacial regions between the oxide and the Au substrate. The AP-XPS revealed the presence of formate in the nanocrytalline α-Fe₂O₃/Au(111) system at elevated temperatures resulting from a reaction between adsorbed CO and OH.

Work performed on ALS Beamline 9.3.2

Citation: Xingyi Deng, Junseok Lee, Congjun Wang, Christopher Matranga, Funda Aksoy, and Zhi Liu, "Reactivity Differences of Nanocrystals and Continuous Films of α-Fe2O3 on Au(111) Studied with In Situ X-ray Photoelectron Spectroscopy" J. Phys. Chem. C, 2010, 114 (51), pp 22619–22623.