Effect of the Composition of the Reaction Atmosphere on the Thermal Stability of Highly Dispersed Gold Particles on an Oxide Support (Au/Fe2O3 System)

Abstract

Gold metal particles were vacuum deposited onto the iron oxide surface and the effect of thermal treatment on the resulting Au/Fe₂O₃ samples at 30–800°C in vacuum and reaction media with different chemical compositions, i.e., 5 mbar of O₂, 5 mbar of CO, and 5 mbar of CO + 5 mbar of O₂, was studied by X-ray photoelectron spectroscopy. During the gold deposition, the increase in the intensity of the Au4f line was shown to be accompanied by its shift toward lower binding energies, which is due to the increase in the particle size of gold. Starting from a certain amount of deposited gold, the binding energy E_b(Au4f_7/2) reaches the value typical of bulk gold metal. During the heating of Au/Fe₂O₃ in vacuum or a reaction medium, fine gold particles agglomerate into coarser ones, which is manifested in the decrease in the relative [Au]/[Fe] atomic ratio. The tendency of gold particles toward agglomeration depends on the composition of the reaction medium: the process proceeds most efficiently in the CO + O₂ mixture and less intensively in CO, and the highest stability was observed upon treatment in O₂. It is assumed that the decrease in the [Au]/[Fe] atomic ratio during the thermal treatment of Au/Fe₂O₃ in CO + O₂, CO, and vacuum could be not only due to agglomeration but also due to the encapsulation of the gold particles by the reduced fragments of the support.