Autor/a:
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Albani, Davide; Li, Qiang; Vilé, Gianvito; Mitchell, Sharon; Almora-Barrios, Neyvis; Witte, Peter T.; López, Núria; Pérez-Ramírez, Javier
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Abstract:
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Gamma-valerolactone (GVL), a versatile renewable compound listed among the top 10 most promising
platform chemicals by the US Department of Energy, is produced via hydrogenation of levulinic acid (LA).
The traditional high-loading ruthenium-on-carbon catalyst (5 wt% Ru) employed for this transformation
suffers from low metal utilisation and poor resistance to deactivation due to the formation of RuOx
species. Aiming at an improved catalyst design, we have prepared ruthenium nanoparticles modified with
the water-soluble hexadecyl(2-hydroxyethyl)dimethylammonium dihydrogen phosphate (HHDMA) ligand
and supported on TiSi2O6. The hybrid catalyst has been characterised by ICP-OES, elemental analysis,
TGA, DRIFTS, H2-TPR, STEM, EDX, 31P and 13C MAS-NMR, and XPS. When evaluated in the continuousflow
hydrogenation of LA, the Ru-HHDMA/TiSi2O6 catalyst (0.24 wt% Ru) displays a fourfold higher reaction
rate than the state-of-the-art Ru/C catalyst, while maintaining 100% selectivity to GVL and no sign of
deactivation after 15 hours on stream. An in-depth molecular analysis by Density Functional Theory
demonstrates that the intrinsic acidic properties at the ligand–metal interface under reaction conditions
ensure that the less energy demanding path is followed. The reaction does not obey the expected
cascade mechanism and intercalates hydrogenation steps, hydroxyl/water eliminations, and ring closings
to ensure high selectivity. Moreover, the interfacial acidity increases the robustness of the material against
ruthenium oxide formation. These results provide valuable improvements for the sustainable production
of GLV and insights for the rationalisation of the exceptional selectivity of Ru-based catalysts |