Rational nanoparticle synthesis to determine the effects of size, support, and K dopant on Ru activity for levulinic acid hydrogenation to γ-valerolactone

With worldwide petroleum resources dwindling and greenhouse gas emissions rising, it is urgent to find renewable replacements for petroleum-derived products. A biomass-derived chemical with high potential as a platform intermediate, γ-valerolactone (GVL) can be readily synthesized by hydrogenation of levulinic acid (LA), itself a common biomass intermediate, using supported Ru catalysts. To date the literature on many novel biomass conversion processes such as the hydrogenation of LA to GVL has focused more on the process and less on the catalyst. The goal of this work was to derive fundamental synthesis–structure–function relationships of Ru catalysts for LA hydrogenation using carbon- and alumina-supported Ru nanoparticles that have been synthesized in a rational, repeatable, scalable way. We have demonstrated that the method of strong electrostatic adsorption (SEA) yields well-dispersed, homogeneously distributed Ru particles with tight particle size distributions over both types of supports. SEA synthesis of well-dispersed nanoparticles results in higher activity than commercial Ru catalysts with higher Ru loadings. The dramatic, beneficial effect of potassium doping is reported for the first time. The carbon support yields higher inherent activity than alumina. Activity as a function of particle size appears to go through a maximum at about 1.5 nm for both supports and suggests hydrogenation of LA is structure sensitive to Ru particle size. Catalyst deactivation after 24 h occurs to significant extents (8–58%) mainly by nanoparticle sintering, but also by minor amounts of K loss in K-doped samples.