The Study of Au/Ni Bimetallic Nanoparticles Using a Combination of XAFS, XRD and SAXS/ASAXS Synchrotron Techniques
Доклады на конференциях
Bimetallic Au/Ni nanoparticles are characterised by a strong size effect and synergism of the catalytic activity towards the allylbenzene isomerization . The Au/Ni nanoparticles prepared by the metal-vapour synthesis (MVS) method as metal-rich blacks and composites supported on various supports were studied via XAFS, XRD and SAXS/ASAXS techniques.
According to the Au L3-edge XAFS data the local structural environment of Au atoms in Au/Ni nanoparticles is close to that in the bulk Au. The Au-Au distance (2.78 Å) in Au/Ni nanoparticles is shorter and coordination number is smaller than in bulk Au due to the small particle size. The Au-Ni interaction at 2.74 Å was also observed for Au atoms. According to the Ni K-edge XAFS data the local environment of Ni atoms in Au/Ni nanoparticles is close to that in the nickel oxide NiO.
The XRD data indicate the presence of 1.5-2 nm bulk Au nanoparticles in the bimetallic Au/Ni nanocomposites, whereas nickel oxide phase is completely amorphous. The SAXS signal is dominated by Au and thus it provides a straightforward estimate of gold nanoparticle size that agrees well with the XRD data. The anomalous SAXS technique near the Ni K-edge was used to distinguish the contribution of Ni atoms in Au/Ni nanocomposites. It reveals a wide size distribution of Ni aggregates in the range of 5-50 nm with a maximum at 20 nm.
The combination of XAFS, XRD and SAXS/ASAXS techniques allows one to make a conclusion on Au@NiO core-shell model structure of the bimetallic Au/Ni nanoparticles.
The results on MVS-synthesised Au/Ni nanoparticles were compared with transformations of bimetallic cluster compound [Au6Ni32(CO)44]6− in acetonitrile solution giving rise to Au/Ni bimetallic nanoparticles as monitored by in situ EXAFS .