Aspects of the interaction between Au and Fe in supported catalysts applied to the preferential CO oxidation

Au and/or Fe supported on.-Al2O3 catalysts were prepared, and the sequence of Au deposition and Fe impregnation were varied for the bimetallic catalysts. An investigation over the aspects of the interaction between Au and Fe in these catalysts applied to the preferential oxidation of CO was performed by characterization of the catalysts using textural analysis, ex situ and in situ X-ray diffraction (XRD), temperature-programmed reduction (TPR), transmission electronic microscopy (TEM), and in situ X-ray absorption near edge structure (XANES). The sequence of Au deposition and Fe impregnation directed the formation of distinct FeOx phases in Au-Fe supported catalysts. XANES spectra revealed the hematite phase formation is predominant in the AuFeAl catalyst, while there is a mixture of hematite and magnetite phases in the FeAuAl catalyst after the preparation and calcination in synthetic air. This was determinant in the type of interaction of these FeOx phases with the Au nanoparticles, where Au delta(+)-Fe3+ oxides interaction was found being responsible for providing more active and selective sites and enable well dispersed Au nanocrystals on stream. TEM images and in situ DRX showed Au degrees nanoparticles agglomeration in FeAuAl catalyst, while well dispersed Au degrees nanoparticles (2-20 nm) are present in AuFeAl catalyst, both before and after reaction. The previous reduction treatment in H-2 of the Au-based catalysts was crucial to reach higher conversions at lower temperatures and higher CO2 selectivity, which was attributed to the interaction of Au nanoparticles and FeOx species. XANES analysis showed FeOx phases composition are also modified by prior reduction, what did not affect the interaction between Au-Fe obtained in the synthesis. Under CO-PROX conditions, FeOx phases composition in the catalysts are preserved.