Control in Advanced Biofuels Synthesis via Alcohol Upgrading: Catalyst Selectivity to n-Butanol, sec-Butanol or Isobutanol

Abstract

Ruthenium complexes with tetradentate PNNP donor ligands demonstrate a marked change in selectivity compared to analogous bis bidentate PN complexes in Guerbet catalysis, producing mixtures of n-butanol (17 %), sec-butanol (14 %) and ethyl acetate (66 %) rather than the usual 90 %+ selectivity to n-butanol. Tridentate PNP ruthenium complexes such as [Ru(H)(Cl)(CO)(Ph2PCH2CH2NHCH2CH2PPh2)] also produce sec-butanol and, in optimized conditions (120 °C, 10 mol% NaOEt base), achieve 71 % selectivity to this butanol isomer. The same tri- and tetradentate complexes are efficient catalysts for the conversion of methanol/ethanol mixtures to isobutanol (up to 97 % selectivity). In this way, judicious choice of ligand within this general catalyst family allows selectivity to three butanol isomers of interest as fuel molecules.