γ-Valerolactone (GVL) is readily obtained by the hydrogenation of levulinic acid (LA) and is considered a sustainable platform chemical for the production of biobased chemicals. Herein, the performance and stability of Ru-based catalysts (1 wt % Ru) supported on TiO 2 (P25) and ZrO 2 (monoclinic) for LA hydrogenation to GVL is investigated in the liquid phase in batch and continuous-flow reactors using water and dioxane as solvents. Particular attention is paid to the influence of possible impurities in the LA feed on catalyst performance for LA hydrogenation. Benchmark continuous-flow experiments at extended times on-stream showed that the deactivation profiles are distinctly different for both solvents. In dioxane, the Ru/ZrO 2 catalyst is clearly more stable than Ru/TiO 2, whereas the latter is slightly more stable in water. Detailed characterization studies on spent catalysts after long run times showed that the deactivation of Ru/TiO 2 is strongly linked to the reduction of a significant amount of Ti 4+ species of the support to Ti 3+ and a decrease in the specific surface area of the support in comparison to the fresh catalyst. Ru/ZrO 2 showed no signs of support reduction and displayed morphological and structural stability; however, some deposition of carbonaceous material is observed. Impurities in the LA feed such as HCOOH, H 2SO 4, furfural (FFR), 5-hydroxymethylfurfural (HMF), humins, and sulfur-containing amino acids impacted the catalyst performance differently. The results reveal a rapid yet reversible loss of activity for both catalysts upon HCOOH addition to LA, attributed to its preferential adsorption on Ru sites and possible CO poisoning. A more gradual drop in activity is found when cofeeding HMF, FFR, and humins for both solvents. The presence of H 2SO 4, cysteine, and methionine all resulted in the irreversible deactivation of the Ru catalysts. The results obtained provide new insights into the (ir)reversible (in)sensitivity of Ru-based hydrogenation catalysts to potential impurities in LA feeds, which is essential knowledge for next-generation catalyst development.
- Biobased chemicals
- Catalyst deactivation
- Catalyst stability
- Ruthenium catalysts
- Zirconia and titania supports