(72c) ZrO2 Is Preferred over TiO2 As Support for the Ru-Catalyzed Hydrogenation of Levulinic Acid to γ-Valerolactone

In the last few years, γ-valerolactone (GVL), readily obtained by the hydrogenation of levulinic acid (LA), has attracted the attention of both academic researchers and industries because of its possible use in different applications related to the chemical industry (e.g., as fuel additives, food ingredients, nylon intermediate or as a solvent). Numerous approaches have been examined for LA hydrogenation, with the main focus in most cases on obtaining high GVL yields by variation of either the active phase or the catalyst support. Studies focusing on catalyst stability are much more limited in number. Indeed, while high activity/selectivity for GVL can relatively easily be achieved with most of the reported catalysts, as well as with commercial ones (e.g., Ru/C), stable performances especially under more industrially-relevant conditions is much harder to achieve. Long-term exposure to relatively harsh, polar conditions, as well as the use of non-pure, real LA feeds containing impurities from previous process steps indeed pose significant challenges to catalyst stability.

Herein, we present a study of catalyst stability and performances for the hydrogenation of LA to GVL of a Ru/ZrO₂ catalyst [1-2]. Catalyst performance has been compared with commercial Ru/C and a self-synthesized Ru/TiO₂ catalyst, which can generally considered as benchmark catalysts for this process. All catalysts show high GVL yields under standard conditions. Large differences were seen in catalyst stability; though, Ru/ZrO₂ maintanied its stability and high GVL yields were obtained even after five recycling tests. Remarkably, in the fresh Ru/ZrO₂ catalyst, Ru was found to be fully atomically dispersed on the fresh catalyst even at 1 wt.% Ru loading, with some genesis of Ru nanoparticles being observed upon recycling. Notably and in strong contrast to the benchmark catalysts (Ru/C and Ru/TiO₂), the Ru/ZrO₂ catalyst can efficiently perform the hydrogenation of LA even in the presence of impurities in the LA feed, e.g., H₂SO₄, salts (Na₂SO₄, NaCl, and H₃PO₄), and organic compounds/contaminants derived from fractions of the biomass, which have been reported as impurities existing in real streams. To better understand these remarkable results with regards to catalytic performance, an extensive catalyst characterizatin study was performed to provide more insights into the relation between structure, performance, and long-term stability of the catalysts.

[1] J. Ftouni, A. Muñoz-Murillo, A. Goryachev, J. P. Hofmann, E. J.M. Hensen, L. Lu, C. J. Kiely, P. C.A. Bruijnincx, B. M. Weckhuysen. ZrO₂ is preferred over TiO₂ as support for the Ru-catalyzed hydrogenation of levulinic acid to γ-valerolactone, submitted.

[2] J. Ftouni, P. C.A. Bruijnincx, B. M. Weckhuysen. Method for preparing a chemical compound using a ruthenium metal catalyst on a zirconium oxide support in the presence of a contaminant, PCT/EP2016/054031.