Enhanced stability and activity in the upgrading ethanol to n-butanol using a ruthenium polyphenylene catalyst

Bioethanol upgrading to n-butanol is catalysed by homogeneous catalysts under mild solventless liquid phase conditions, at which heterogeneous catalysts have poor performance. Here a heterogeneous catalyst, initially comprised of a Ru(bipy) complex incorporated into a polyphenylene support, gave a catalytic performance (TON of 3565 Ru⁻¹ and 82 % n-butanol selectivity) that exceeded contemporary homogeneous and heterogeneous catalysts. Catalyst deactivation by water byproduct inhibition was improved by removal of water, via recharging the reactor with fresh ethanol, or by the co-addition of molecular sieve. The Ru polyphenylene catalyst showed greater stability in the presence of molecular sieve compared to the homogeneous catalyst, enabling high butanol yields. Characterisation showed a structural transformation of the single atom Ru(bipy) into 2.6 nm Ru(0) nanoparticles after 16 h reaction. While the Ru(0) had moderate recyclability (TON of 1000 Ru⁻¹) the initial highly active species seen in the fresh catalyst are not stable.