Bimetallic Supported Catalysts from Single-source Precursors - Atomically-Precise Methods for Synthesis of Solid Catalysts - page 73

membrane fuel cell (PEMFC) and was shown to exhibit improved CO
tolerance compared to a commercial Pt/C anode catalyst. Similarly, two
mixed Pt-Sn clusters were used as single-source precursors for Pt-Sn/Vulcan
carbon nanocomposites. 62 The nanoparticles of 5-8 nm diameter were
composed of bimetallic Pt-Sn alloy with a loading of 15 wt% but with the
concomitant presence of PtP 2 or Pt metal. Their performance as electro-
oxidation catalysts in direct methanol fuel cell was comparable to a catalyst
prepared by conventional methods.
Finally, the group of B. F. G. Johnson, in collaboration with J. M. Thomas,
has also been a major contributor in cluster-derived supported catalysts
since the late 1990s. Mixed-metal clusters were mainly immobilized within
the mesopores of the siliceous MCM-41 and converted thermally to bi-
metallic nanoparticles, which presented interesting catalytic activities in a
range of reactions. The first examples concerned silver-ruthenium 63,64 and
copper-ruthenium 65 clusters. Activation was followed in situ by infrared
spectroscopy and EXAFS. Infrared spectroscopy is indeed very useful to
characterize carbonyl clusters given the very strong bands associated with
CO stretching: the activation can be associated with disappearance of these
bands. The structural parameters retrieved from the EXAFS data indicated
retention of discrete Ag 3 Ru 10 particles in the activated catalyst prepared from
the [Ag 3 Ru 10 C 2 (CO) 28 Cl] 2 cluster. Also from the EXAFS data, a model of the
activated Cu-Ru 1.5 nm particles was proposed (Figure 3.7) where the Cu
atoms are in close contact with the surface through Cu-O bonds (there was
no direct indication in the EXAFS data for any Ru-O shells). Annular dark-
field STEM electron microscopy allowed visualization of the particles very
clearly. The idea of using the more oxophilic metal as an anchoring point for
the nanoparticles was thus successfully used here, with no indication of
sintering or fragmentation. The obtained Cu-Ru/MCM-41 catalyst was found

d n 9 r 4 n g | 5

.

Figure 3.7 Model of the activated Cu-Ru nanoparticles deposited within the meso-
pores of MCM-41 from the cluster precursor [Ru 12 C 2 (CO) 32 Cu 4 Cl 2 ] 2 .