Levulinic acid (LA) and formic acid (FA) are highly abundant in hydrolysates obtained from lignocellulosic biomass [1]. LA can be directly converted to γ-valerolactone (GVL) via catalytic aqueous-phase hydrogenation [2]. GVL itself represents one of the most promising renewable platform chemicals in modern biorefineries. The aqueous-phase hydrogenation of LA requires a bifunctional catalyst, containing a hydrogenation and an acid functionality typically provided by noble metals and an acidic support, respectively [3]. However, the hydrothermal stability of the catalysts is one of the major challenges in the aqueous-phase hydrogenation of LA due to the low pH value of the reaction mixture, i.e., pH = 2 [3]. ZrO2-based catalysts were reported to exhibit high hydrothermal stability in hot liquid water above 473 K [3]. Thus, in the present work, bifunctional, monometallic Pt catalysts supported on mesoporous ZrO2 with different textural properties, phase composition and acid site density were prepared and investigated in the aqueous-phase in-situ hydrogenation of LA using FA as reducing agent. In the in-situ hydrogenation of LA with FA an increase in acid site density (ASD) and specific surface area (ABET) of the ZrO2 results in an increase in LA conversion. Over the catalyst with the highest ABET, i.e., 204 m2 g-1; ASD, i.e., 136 µmol g-1, and ZrO2 in the tetragonal phase (1.6Pt/ZrO2), the highest LA conversion (84%) and GVL yield (82%) were achieved at 493 K after 24 h. An increase in reaction temperature from 493 K to 533 K significantly affects the conversion of LA as well as the GVL yield. While at 493 K LA is selectively converted to GVL, at 533 K GVL is obtained with a yield of 68%. At this temperature, pentanonic acid is formed with a yield of 22% suggesting that at elevated temperature LA conversion takes place by two different reaction pathways. Furthermore, the catalyst 1.6Pt/ZrO2 exhibits stability under the harsh reaction condition, i.e., after the 1st reuse no change in the LA conversion and GVL yield as well as in the crystal structure and phase composition of the support is detected.

ZrO2-based catalysts with enhanced hydrothermal stability for the aqueous-phase In-situ hydrogenation of levulinic acid

255th National Meeting (2018)

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