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

• Published in: Kinetics and catalysis 2017-11, Vol.58 (6), p.809-815
• Main Authors: Smirnov, M. Yu, Vovk, E. I., Kalinkin, A. V., Bukhtiyarov, V. I.
• Format: Article
• Language: English
• Subjects: Agglomeration; Binding energy; Catalysis; Chemistry; Chemistry and Materials Science; Composition effects; Gold; Heat treatment; Hematite; Iron oxides; Metal particles; Physical Chemistry; Thermal stability
• ISSN: 0023-1584; 1608-3210
• DOI: 10.1134/S0023158417060106

Gold metal particles were vacuum deposited onto the iron oxide surface and the effect of thermal treatment on the resulting Au/Fe 2 O 3 samples at 30–800°C in vacuum and reaction media with different chemical compositions, i.e., 5 mbar of O 2 , 5 mbar of CO, and 5 mbar of CO + 5 mbar of O 2 , was studied by X-ray photoelectron spectroscopy. During the gold deposition, the increase in the intensity of the Au4 f 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 (Au4 f 7/2 ) reaches the value typical of bulk gold metal. During the heating of Au/Fe 2 O 3 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 + O 2 mixture and less intensively in CO, and the highest stability was observed upon treatment in O 2 . It is assumed that the decrease in the [Au]/[Fe] atomic ratio during the thermal treatment of Au/Fe 2 O 3 in CO + O 2 , 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.