Core-Shell Type Magnetically Active Fe3O4@Au Nanoparticles As Supported Nanocatalysts for CO Oxidation

Size-defined and thiol-ligated Au clusters vcan be used to prepare  nanoparticles (NPs) with less than 2 nm in diameter. These materials exhibit distinct quantum confinement effects that differ significantly from bulk Au, for example exhibitingdiscrete electronic electronic structure and molecular properties such as HOMO-LUMO transitions and intrinsic magnetism. These properties may have an interesting effect on catalysis by these clusters.

Recently, dumbbell shaped Au-Fe₃O₄ nanoparticles prepared by colloidal deposition and supported on TiO₂ have been successfully tested as catalysts for CO oxidation[1]. The particle size of Au in that study was 2.5-3.5 nm and that of Fe₃O₄ was about 15-16 nm, and the dumbbell shape ensured a strong interaction between the metals.  In such NPs, a strong interaction exists between Au and Fe₃O₄ due to the epitaxial growth of Fe₃O₄ on Au[1].

Here, we report the catalytic activity of core-shell type SPIONs@Au supported on TiO₂ for CO oxidation. The NPs were synthesized as described earlier[2, 3] by modifying a reported method for the synthesis of these particles[4]. The Au/Fe₃O₄ particles were impregnated on TiO₂ (P25, Degussa) to give Au/Fe₃O₄/TiO₂ catalysts. These catalysts were treated in an oxidative environment at 300°C, 400°C, and 500°C, respectively before CO oxidation to remove the sulfur ligands. Fresh and treated catalysts were characterized by HRTEM, XPS, XRD, and by CO oxidation. Results show that Au/Fe₃O₄/TiO₂ is an active catalyst for CO oxidation, only if calcined at 300°C. Other treatment methods sintered the catalysts, which results in no catalytic activity.

References:

[1]        H. Yin, C. Wang, H. Zhu, S.H. Overbury, S. Sun, S. Dai, Chemical Communications (2008)

              4357-4359.

[2]        F. Mohammad, G. Balaji, A. Weber, R.M. Uppu, C.S.S.R. Kumar, The Journal of Physical

             Chemistry C. 114 (2010) 19194-19201.

[3]        C.S.S.R. Kumar, F. Mohammad, The Journal of Physical Chemistry Letters. 1 (2010) 3141-3146.

[4]        WangWang, J. Luo, Q. Fan, M. Suzuki, I.S. Suzuki, M.H. Engelhard, Y. Lin, N. Kim, J.Q. Wang,

              C.-J. Zhong, The Journal of Physical Chemistry B. 109 (2005) 21593-21601.