(312b) Fe-Promoted Au/Rutile for the Water-Gas Shift Reaction

The water-gas shift reaction (WGS) is an important reaction for hydrogen production and fuel cell applications¹, which are important for renewable energy. Au supported on oxides has been identified as an active catalyst for WGS. Supports play an important role in not only changing the WGS rates, but also modifying the types and chemical nature of the active sites^2,3. Previous work has shown that Fe doping can promote the CO oxidation rate over Au/TiO₂ catalyst⁴. Here, a series of Fe-doped rutile (TiO₂) catalysts ranging from 0.25wt% to 5wt% Fe were loaded with ~1wt% Au and tested for WGS. WGS rates per mole of Au at 120 ^oC showed maximum promotion by a factor of 4 for 1wt% Fe content. Significant changes in kinetic parameters were observed with varying Fe content. Apparent orders with respect to CO decreased progressively and apparent activation energy increased progressively with Fe content increasing from 0 wt% to 5 wt%. As CO order decreased, WGS rates first increased, reached maximum at CO order about 0.3 and then decreased. From previous work, WGS rates over supported Au are influenced by the Au particle sizes^2,3, but for the catalysts reported here, similar average particle sizes (2.0±0.5 nm) obtained from Transmission Electron Microscopy (TEM) excluded the particle size effects as the source of the observed changes.  Operando Fourier Transform Infrared Spectroscopy (FTIR) was performed on the 1wt% Fe-doped catalyst and the result was compared with Au supported on un-doped rutile.  IR peaks at wavenumbers of 2097 cm^-1, 2044 cm^-1, 1967 cm^-1 and 1888 cm^-1 were observed. The peak at 2097 cm^-1 can be assigned to CO adsorbed on metallic Au while the lower frequencies of 2044 cm^-1 and 1967 cm^-1 can be associated with  CO adsorbed on partially negatively charged Au. The IR bands at lower frequencies were stronger than the corresponding peaks of Au supported on un-doped rutile and thus suggest a participation of Fe in the neighborhood of the site. Thus, the results showed that Fe-doping can modify the CO adsorption properties of Au/Rutile and that WGS rates can be correspondingly promoted with appropriate Fe content.