Abstract
We studied the solvent-free hydrogenation of levulinic acid to γ-valerolactone with the Shvo catalyst involving comparative catalysis, DFT, and LCA.
Highlights
While for the past 150 years many of our fuel, drug, and material needs have been satisfied with fossil-based products, the need to find sustainable bio-based alternatives is everincreasing with dwindling resources, accelerating global warming, and increasing global turmoil.[1]
To pursue our findings regarding the activity of the Shvo-type ruthenium catalysts, it was decided to test all three possible precursors. These can be synthesized from triruthenium dodecacarbonyl and tetraphenylcyclopentadienone in refluxing toluene, methanol, or heptane, to yield the monomeric [2,3,4,5-Ph4(η4-C4CO)]Ru(CO)[3] (Ru-1), and the dimeric species {[2,3,4,5-Ph4(η4-C4CO)]2H}Ru2(CO)4-(μ-H) (Ru-2) and {[2,3,4,5Ph4(η4-C4CO)]Ru(CO)2}2 (Ru-3), respectively (Scheme 2, ‘Synthesis’).[29]
Despite the lower activity of Ru-1 compared to its dimeric homologues, we selected this catalyst precursor for further investigation on the basis of the synthetic yields, as well as possible future applications of Shvo type complexes with substituents on the 2- and 5-position, which are too large to allow the dimer formations seen for Ru-2 and Ru-3.30 In addition, this choice gave us the opportunity to elucidate the relation between requiring in situ decarbonylation of Ru-1 and the inhibited levulinic acid (LA) conversion (63.0%), and how to overcome it
Summary
While for the past 150 years many of our fuel, drug, and material needs have been satisfied with fossil-based products, the need to find sustainable bio-based alternatives is everincreasing with dwindling resources, accelerating global warming, and increasing global turmoil.[1]. Several in situ catalysts derived from Ru(acac)[3] and phosphine ligands were shown to be highly efficient by the groups of Horváth,[18] Leitner,[19] Mika,15a,20 and Beller,15b whereas full conversions to GVL were selectively achieved under 80–100 bar H2 pressure and temperatures of 135–160 °C. We questioned how the choice of hydrogen donor under solvent-free conditions affects the reaction in terms of catalytic performance as well as environmental impact. We established the solvent-free H2-mediated selective hydrogenation of LA to GVL using the monomeric Shvo catalyst precursor Ru-1 in this work, and optimized it in terms of temperature, H2-pressure, and catalyst loading. A LCA evaluating the use of each hydrogen donor in this context was performed
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