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X-ray spectroscopy

The structural determination of gold catalytic nanosystems by XAFS spectroscopy method

Speakers

  • Dr. Vladimir KRIVENTSOV

Primary authors

Content

The structural determination of gold catalytic nanosystems by XAFS spectroscopy method

V.V. Kriventsov 1), D. A. Bulushev 1), B.N. Novgorodov 1), D.P. Ivanov 1), D.G. Aksenov 1), D.A. Zyuzin 1), S.A. Nikolaev 2), A. Simakov 3), A.V. Chistyakov 4), O.V. Arapova 4), M.V. Tsodikov 4)

1) Boreskov Institute of Catalysis SB RAS, Novosibirsk, Russia 2) Lomonosov Moscow State University, Department of Chemistry, Moscow, Russia 3) Centro de Nanociencias y Nanotecnologia, UNAM, Ensenada, B.C., Mexico 4) Topchiev Institute of Petrochemical Synthesis, RAS, Moscow, Russia

This work is devoted to a detailed structural study of the nanosized Au, AuMe stabilized forms located on oxide supports by XAFS method. It is a well known fact that metallic gold is most inert among the precious metals due to its electronic structure, nevertheless the nanosized Au, Au-Me forms located on oxide supports may be used as very active catalysts for numerous industrially important reactions. These systems are very promising for complex organic synthesis, selective isomerization reactions and for processes of environmental catalysts, such as, CO oxidation and selective conversion of secondary alcohols. Reliable analysis of the nature of gold forms is extremely important for design of new effective gold based catalysts for different industrial applications. Synthesis of low-percentage ~ 0.1-2% Au, Au-Me samples was carried out under varying preparation methods (impregnation, deposition-precipitation with urea, direct ion exchange), calcination temperatures and activation methods. All XAFS spectra (Au-L3 edge) of the studied samples were recorded at SSTRC, Novosibirsk. The state of metal components and the local Au structure arrangements of the prepared catalysts were studied. The Au-O, Au-Au, Au-Me interatomic distances and corresponded coordination numbers were established. All possible structural models were discussed. It was shown that different stabilized gold forms located on oxide supports were formed, most probably depending on a sample prehistory: Au(3+) cations, having octahedral oxygen surrounding and metallic Au-Au, Au-Me nanoparticles ~10-100Å. Some correlations between catalytic activities and structural functional properties of the studied samples were shown. Additionally, samples of catalysts were characterized by the HRTEM, EDX, XRD, XPS methods. The data of all methods are in a good agreement. This work was conducted within the framework of the budget project #АААА-А17-117041710078-1 for Boreskov Institute of Catalysis. Vladimir Kriventsov thanks to the Russian Foundation for Basic Research for support of the analysis of the XANES data (projects No. 16-03-01139, 17-33-50198, 18-03-01251).