Reaction mechanism of aqueous-phase conversion of γ-valerolactone (GVL) over a Ru/C catalyst

The present work explores the reaction pathways of γ-valerolactone (GVL) over a supported ruthenium catalyst. The conversion of GVL in aqueous phase over a 5% Ru/C catalyst was investigated in a batch reactor operating at 463K under 500–1000psi of H2. The main reaction products obtained under these conditions were 2-butanol (2-BuOH), 1,4-pentanediol (1,4-PDO), 2-methyltetrahydrofuran (2-MTHF) and 2-pentanol (2-PeOH). A complete reaction network was developed, identifying the primary and/or secondary products. In this reaction network, production of 2-BuOH via decarbonylation of a ring-opened surface intermediate CH3CH(O*)(CH2)2CO* is clearly the dominant pathway. From the evolution of products as a function of reaction time and theoretical (DFT) calculations, a mechanism for the formation of intermediates and products is proposed. The high sensitivity of 2-BuOH production to the presence of CO, compared to a much lower effect on the production of the other products indicates that the sites responsible for decarbonylation are particularly prone to CO adsorption and poisoning. Also, since the decarbonylation rate is not affected by the H2 pressure it is concluded that the direct decarbonylation path of the CH3CH(O*)(CH2)2CO* intermediate does not required a previous dehydrogenation step, as is the case in decarbonylation of short alcohols.