MoOx-decorated Ru/TiO2 with a monomeric structure boosts the selective one-pot conversion of levulinic acid to 1,4-pentanediol

Abstract

Molybdenum oxide-decorated ruthenium on titanium oxide (Ru–(y)MoO_x/TiO₂) catalysts with monomeric structure exhibited high efficiency and selectivity for the selective synthesis of 1,4-pentanediol (1,4-PeD) via the one-pot conversion of levulinic acid (LA) under mild reaction conditions. Ru–(y)MoO_x/TiO₂ catalysts (y = 0.24–1.27 wt%) were synthesized via a hydrothermal method at 150 °C for 24 h, followed by calcination under N₂ stream at 30–500 °C (ramping 4 °C min⁻¹) and reduction with H₂ at 500 °C for 1.5 h. A low Mo co-loading of 0.24–0.47 wt% not only improved the catalytic activity (the reaction rate of LA conversion) but also significantly enhanced the selectivity of 1,4-PeD. Further increase in the Mo co-loading (0.91–1.27 wt%) resulted in a slight decrease of both LA conversion and 1,4-PeD yield. Ru–(0.47)MoO_x/TiO₂ (0.47 is Mo co-loaded (wt%); Mo/Ru = 1 : 10.5) was found to be the best catalyst with a calculated rate constant of 1.4132 h⁻¹, which is approximately 5 times higher than that of unmodified Ru/TiO₂ catalyst (0.2605 h⁻¹). Over the best catalyst, a high yield of 1,4-PeD (81%) at 110 °C and 40 bar H₂ after 3 h was obtained, and the yield of 1,4-PeD significantly increased to 91% when the reaction time was prolonged to 6 h. The Ru–(0.47)MoO_x/TiO₂ catalyst is reusable and can be reactivated by flowing H₂ at 500 °C for 1 h with no loss of catalytic activity.