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L. Vilcocq et al. / Catalysis Today 189 (2012) 117–122
present in the aqueous phase cannot be identified in this case;
we suggest that it could be present in the form of oligomers, not
analysed here. When platinum is added to the catalytic system,
the major aqueous compounds are alcohols, followed by ketones
and heterocycles. Poly-oxygenated molecules such as isosorbide
are present as traces. The carbon distribution between alcohols,
ketones and heterocycles is a function of the metal/acid balance:
heterocycles decreases when the platinum loading increases. The
proportion of ketones is higher with the 25:75 mechanical mixture
but is similar for the two others. The identification ratio as defined
in Table 3 (proportion of identified compounds in aqueous phase
compared to the TOC analysis) is 100% for the 100:0 mechanical
mixture but lower for the two others, which means that a part of the
aqueous compounds remains unknown. This is in line with other
published results [15]. The hypothesis of other heterocyclic com-
present too. The presence of carboxylic acids was also detected by
GC-FID analysis. The presence of acids is mentioned in literature
[13,23], but their formation is not clearly explained. The dispro-
portionation proposed by Wawrzetz et al. is a viable hypothesis
[13].
decarbonylation/decarboxylation pathway cannot be completely
eliminated when using platinum. New metallic phases are needed,
such as for example palladium or rhenium-based bimetallic cata-
lyst. Additionally, the yield of alcohols in the aqueous phase is high
(28 carbon%), indicating that the acid function is still deficient and
cannot totally dehydrate alcohols.
4. Conclusion
APD/H Pt/SiO2–Al2O3 catalytic system has been studied. We
demonstrated that the metal/acid balance has a great impact on
selectivities. Alkane selectivity depends on two main conditions:
first, the metal phase has to be highly hydrogenating and should
not favour the C–C cleavage reactions; secondly, the acid phase
has to be strong enough to catalyse the dehydration of alcohols.
However, the C–C cleavage properties of platinum did not allow
to avoid undesired CO2 production. In the future, new acid and
metallic phases have to be developed to overcome the C–C cleavage
issue. A well-designed catalytic system should be able to produce
selectively long-chain hydrocarbons.
Acknowledgments
The authors thank K. Gaillard for technical help and IFP Energies
Nouvelles for financial support.
3.4. Discussion
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the 50:50 mechanical mixture of Pt/SA and SA, the CO2
yield remains important. This means that the dehydrogenation/