metals from the original structure indicating that the essential
integrity of the original double octahedra structure is retained in
the activated form. (There is however, a significant reduction in
the metal–metal distances, compared to the parent cluster
compound, a fact which is consistent with our previous
observations on other bimetallic cluster catalysts). The final
model derived from the simultaneous refinement of both Ru and
Pt edges shows that, apart from the metal–metal contacts, there
are oxygen neighbours; in particular the platinum centres have
one oxygen neighbour for each platinum in the nanoparticle
catalyst and at least one of the ruthenium centres has one oxygen
neighbour in the activated form. This oxygen is undoubtedly
part of the silica support to which the bimetallic nanocluster is
anchored. The final structure is depicted in Fig. 1.
It is seen from Fig. 2 that one of the bimetallic catalysts
prepared by us, Ru10Pt2, is superior in its selectivity to all the
other bimetallic nanocatalysts that we have so far studied. It is
also superior to the monometallic, supported catalysts such as Pt
and Rh. This augurs well for the future use of high-area,
thermally stable, bimetallic nanocatalysts in the wide range of
hydrogenations that may be effected to yield desirable chemical
products from plant crop sources.17,18 It is also of relevance to
point out that -glucose may also serve as a source of hydrogen
D
as recently demonstrated.21
Notes and references
1 K. M. Draths and J. W. Frost, J. Am. Chem. Soc., 1994, 116, 399.
2 J. M. Thomas, R. Raja, G. Sankar, R. G. Bell and D. W. Lewis, Pure
Appl. Chem., 2001, 73, 1087.
3 (a) P. L. Bragd, A. C. Besemer and H. van Bekkum, J. Mol. Catal. A.,
2001, 170, 35; (b) C. Okkerse and H. van Bekkum, Green Chem., 1999,
1, 107.
4 M. T. Musser, Ullmanns Encyclopedia of Industrial Chemistry, Vol. A8,
Wiley-VCH Verlag, Weinheim, Germany, 2000.
5 J. M. Thomas, R. Raja, B. F. G. Johnson, G. Sankar and D. W. Lewis,
Chem. Eur. J., 2001, 7, 2972.
6 D. D. Davis and D. R. Kemp, Kirk-Othmer Encyclopedia of Chemical
Technology, ed. J. I. Kroschwitz and M. Howe-Grant, Vol. 1, 4th edition,
Wiley, New York, 1991.
7 R. E. Dickinson and R. J. Cicerone, Nature, 1986, 319, 109.
8 See for example, (a) K. Sato, M. Aoki and R. Noyori, Science, 1998,
281, 1646; (b) Y. Q. Deng, Z. F. Ma, K. Wang and J. Chen, Green Chem,
1999, 1, 275; (c) N. d’Alessandro, L. Liberatore, L. Tonucci, A.
Morvillo and M. Bressan, New. J. Chem., 2001, 25, 1319; (d) S. O. Lee,
R. Raja, K. D. M. Harris, J. M. Thomas, B. F. G. Johnson and G. Sankar,
Angew. Chem., Int. Ed., 2003, in press.
22
Fig. 1 (A) Typical parent anionic carbonylate of [Ru10Pt2C2(CO)28
] ,
from which naked nanoparticle (10 to 15 Å diameter, depending upon the
constituents of the bimetallic core) catalysts are generated. (B) Fourier
transform fits from the multiple edge EXAFS refinement of the Ru10Pt2
cluster adsorbed on mesoporous silica after activation (see ESI† for
experimental details), and a proposed model for the binding of Ru10Pt2 to
the silica surface based on the EXAFS refinement.12,15 The experimental
data is the full line, the model data is the dotted line.†
9 R. Raja, G. Sankar and J. M. Thomas, J. Am. Chem. Soc., 1999, 121,
11926.
10 M. Dugal, G. Sankar, R. Raja and J. M. Thomas, Angew. Chem., Int. Ed.,
2000, 39, 2310.
11 R. Raja, G. Sankar and J. M. Thomas, Angew. Chem., Int. Ed., 2000, 39,
2313.
12 J. W. Frost, in Green Chemistry, ed. P. T. Anastas and T. C. Williamson,
O. U. P., Oxford, 1998.
13 W. Niu, K. M. Draths and J. W. Frost, Biotechnol. Prog., 2002, 18,
201.
14 Chemical Market Reporter, 2001, 259, 22.
15 D. S. Shephard, T. Maschmeyer, B. F. G. Johnson, J. M. Thomas, G.
Sankar, D. Ozkaya, W. Z. Zhou, R. D. Oldroyd and R. G. Bell, Angew.
Chem., Int. Ed., 1997, 36, 2242.
16 (a) R. Raja, T. Khimyak, J. M. Thomas, S. Hermans and B. F. G.
Johnson, Angew. Chem., Int. Ed. Engl., 2001, 40, 4638; (b) S. Hermans,
R. Raja, J. M. Thomas, B. F. G. Johnson, G. Sankar and D. Gleeson,
Angew. Chem., Int. Ed. Engl, 2001, 40, 1211.
17 J. M. Thomas, B. F. G. Johnson, R. Raja, G. Sankar and P. A. Midgley,
Acc. Chem. Res., 2003, 36, 20 and references therein.
18 J. M. Thomas, R. Raja, B. F. G. Johnson, S. Hermans, M. D. Jones and
T. Khimyak, Ind. Eng. Chem. Res., 2003, in press(web release 3 January
2003).
19 J. M. Thomas and G. Sankar, J. Synchrotron Radiat., 2001, 8, 55.
20 B. F. G. Johnson, S. Hermans and T. Khimyak, Eur. J. Inorg. Chem.,
2003, in press.
21 R. D. Cortright, R. R. Davda and J. A. Dumesic, Nature, 2002, 418,
964.
Fig. 2 The activities and selectivities of the four anchored bimetallic
nanocatalysts (Ru6Pd6, Ru12Cu4, Ru5Pt1, Ru10Pt2) are compared with
commercially available Pt/SiO2 and Rh/Al2O3 for the hydrogenation of
trans,trans-muconic acid to (2). Reaction conditions: substrate ≈ 5.0 g
(dissolved in 100 ml of ethanol); catalyst = 50 mg, H2 pressure = 30 bar,
temp. = 353 K; t = 5 h.
the ESI†). Employing the same model as the starting geometry,
but without the presence of carbonyl ligands (in agreement with
the in situ FT-IR studies which showed that all the bands related
to the carbonyl group disappear upon heating in vacuum at ca.
175 °C), yielded a good fit to the experimental EXAFS data.
This suggests that there is no significant rearrangement of the
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