1424
J.-Y. Ruzicka et al.
Pt : Ru ratios studied. Overall, catalytic activity appears to
depend directly on the amount of platinum in the catalyst.
The most active catalyst was found to be composed of 84 %
platinum by mass (73 % by moles), which may be indicative of a
synergistic effect between the platinum and ruthenium at this
particular ratio.
ICP-MS results showed that an appreciable amount of colloid
was not properly immobilised on the surface of the silica
support, causing metal loading to vary appreciably. Further
work should aim to optimise the method of catalyst immobilisa-
tion, minimising the loss of metal colloid. In addition, there has
not yet been a comprehensive attempt to elucidate the mecha-
nism of phenylacetylene hydrogenation on the surface of the
metal catalyst. A better understanding of how the reactant
molecule interacts with the catalyst surface, based on careful
modelling, may also be key to understanding exactly how any
synergistic effect alters the reaction rate.
Characterisation
Nanoparticles were characterised by TEM using a Philips
CM-200 transmission electron microscope. Samples were pre-
pared by suspending activated catalyst in a small amount of
methanol and delivering a small drop of the slurry onto a Cu 300
mesh TEM sample grid covered with a holey carbon film.
ICP-MS analyses were performed using an Agilent 7500cx
equipped with an octopole collision cell (Agilent Technologies
Inc., Tokyo, Japan). Each catalyst (100 mg) was first digested in
a concentrated solution of hydrochloric and nitric acid (aqua
regia) for 3 h at 808C. This solution was made up to 50 mL and
then diluted thirty times with dilute (6 %) aqua regia. 200 mL of
this solution was withdrawn and made up to 6 mL with 6 % aqua
regia. The resultant solution was analysed by ICP-MS for
platinum and ruthenium.
Catalysis
Catalyst (50 mg) was added to 1 mL of phenylacetylene,
38.75 mL of dried methanol and 250 mL of decane internal
standard in a 100 mL Teflon-lined Parr pressure reactor. This
was heated to 408C under argon with stirring of 1450 rpm. Once
temperature was reached, the system was flushed with hydrogen
before being pressurised with 10 bar of hydrogen gas. The
pressure was monitored using a Parr 4842 pressure monitor. The
reaction was allowed to proceed for one hour.
The reaction products were centrifuged to remove the cata-
lyst. The supernatant was analysed using a Shimadzu GC-2010
gas chromatograph equipped with a Restek Rxi-5Sil MS
column. Helium was used as a carrier gas, with a flow rate of
17.4 cm sꢃ1. The injection volume was 1 mL, the injection
temperature was 2008C, the FID temperature was 3008C and
the column was kept at 808C.
Experimental
Materials
H2PtCl6ꢁ6H2O (BDH), RuCl3 (Precious Metals Online),
PVP (MW E 40000, Sigma-Aldrich), ethyl benzene (BDH),
styrene (Merck), and phenylacetylene (Aldrich) were used as
obtained. All solvents were analytical grade unless noted
otherwise. Acids used for digestion were Merck Suprapur HNO3
and Tracepur HCl.
Silica gel was obtained from Scharlau. It was recorded to
have an overall particle size of 0.04–0.06 mm, a mean pore
2
diameter of 60 A, and a surface area of 500 m g
ꢃ1
˚
.
Methanol used for catalysis was dried with iodine and
magnesium.[18]
Decane used as the internal standard was obtained from
Sigma-Aldrich (.99 %).
A series of five standards of phenylacetylene, styrene, and
ethylbenzene were prepared in methanol, with concentrations
ranging from 1 mM through 500 mM. These standards were
used to calibrate the GC, using the conditions described above.
Synthesis
Metal solutions were made by dissolving ruthenium or platinum
precursor (RuCl3 or H2PtCl6 respectively) in methanol to
achieve a concentration of 2 ꢂ 10ꢃ3 mol Lꢃ1. PVP was added to
Acknowledgements
The authors acknowledge the University of Canterbury and the MacDiarmid
Institute for funding, as well as the help of Robert Stainthorpe with ICP-MS
measurements.
these solutions to
(monomeric units).
a
concentration of 4 ꢂ 10ꢃ2 mol Lꢃ1
Solutions containing 2 ꢂ 10ꢃ4 mol of metal were formed by
combining various ratios of these two solutions at room temper-
ature, and 1 ꢂ 10ꢃ3 mol of sodium borohydride (as solid) was
added quickly to reduce the metal. The resulting colloid was
stirred for one hour to ensure complete reduction and nanoparti-
cle formation.
References
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The amount of silica used for each immobilisation was calcu-
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Silica was added to a colloidal solution in methanol and
stirred for one hour. Methanol was removed by vacuum and the
powder left was calcined for 2 h under vacuum at 2008C. After
cooling to room temperature, methanol (100 mL) was added and
the mixture stirred for a further 30 min to remove surfactants and
any colloidal nanoparticles that had not been immobilised.
Following overnight flocculation of the solid, the methanol
wash was carefully removed by syringe, and the powder was
dried under vacuum.