Ruthenium-catalyzed hydrogenation of levulinic acid : Influence of the support and solvent on catalyst selectivity and stability

The catalytic performance of 1 wt% Ru-based catalysts in the hydrogenation of levulinic acid (LA) has been studied at 40 bar H-2 and 473 K. This was done by assessing the influence of the support acidity (i.e., Nb2O5, TiO2, H-beta, and H-ZSM5) and solvent (i.e., dioxane, 2-ethylhexanoic acid (EHA), and neat LA). The Ru/TiO2 gave excellent selectivity to gamma-valerolactone (GVL) (97.5%) at 100% conversion and was remarkably stable even under severe reaction conditions. Ru/H-ZSM5 showed a 45.8% yield of pentanoic acid (PA) and its esters in dioxane, which is the first example of this one-pot conversion directly from LA at 473 K. The gradual deactivation of zeolite-supported catalysts in EHA and neat LA was mainly caused by dealumination, as confirmed by Al-27 MAS NMR. Coke buildup originated from angelicalactone and, remarkably, occurred preferentially in the zigzag channels of H-ZSM5 as shown by systematic shifts in the XRD patterns. The GVL ring-opening step is considered to be the rate-determining step on the pathway to PA, necessitating an acidic support. (C) 2013 Elsevier Inc. All rights reserved