experiments. The catalytic performance of the RuCl3/
[EMMIM][OAc] system remained unaffected when the reaction
was performed in presence of Hg (see Supporting Information
for details†). Moreover, the outcome of the TEM analysis and
Hg poisoning experiments were also indirectly corroborated
by the strong influence of different ionic liquid anions on the
catalytic performance (see Table 1). The latter, indeed, could
well be understood when taking into account a homogeneous
catalytic species with the ionic liquid anion acting as a more or
less coordinating part in the Ru(II) complex ligand sphere.
formic acid (0.46 g), sodium formate (0.068 g) and the catalyst
(10.1 mmol ruthenium) were charged into the reactor. The system
was purged with nitrogen and then pressurized to 12 bar. Then,
the reactor was placed in a heating block and heated at the
desired temperature. The reaction progress was monitored by a
digital manometer. Conversion and TOF were calculated from
the pressure values and the GC analysis data (knowing the
total reactor volume, and using the ideal gas law). For the
recycling experiments, after cooling and venting, formic acid
(0.50 g) was added to the reaction mixture. Then the reactor
was newly purged with nitrogen and finally pressurized with 12
bar of nitrogen. The reaction was re-started by switching on the
heating.
Conclusion
In this study, we identified and investigated an outstanding
simple, active and recyclable ionic liquid based system for
the catalytic decomposition of formic acid. The most efficient
system, RuCl3 dissolved in [EMMIM][OAc], was shown to
produce hydrogen and carbon dioxide as the only products and
was recyclable for at least nine recycle runs. During these recycles
no sign of deactivation or change in selectivity was observed.
Based on the anion variation study, TEM measurements,
Hg poisoning experiments and catalytic runs with different Ru
catalyst precursors we conclude that the active catalyst in the
ionic liquid is an homogeneously dissolved Ru(II) complex with
the ionic liquid taking part in the stabilization of the metal centre.
It is worth noting that this simple catalytic system formed solely
of RuCl3 dissolved in [EMMIM][OAc] exhibits very attractive
Acknowledgements
The authors like to thank the Deutsche Forschungsgemeinschaft
(DFG) that has provided through its Erlangen Excellence Clus-
ter “Engineering of Advanced Materials” significant support
for this project. M. B. acknowledges support by the Erlangen
Graduate School of Molecular Science.
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◦
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General reaction procedure
The reactions were carried out in steel autoclaves with a glass
inlet and a total volume of 28 mL. The ionic liquid (3.0 g),
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The Royal Society of Chemistry 2011
Green Chem., 2011, 13, 1411–1415 | 1415
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