Selectivity control under continuous flow: from methyl levulinate to gamma-valerolactone and methyl pentanoate using functionalized Ru/hydrochars

• A continuous-flow system enables selectivity control in levulinic acid conversion. • The process yields three main products: γ-valerolactone (GVL), methyl levulinate (ML) and methyl pentanoate (MP). • Selectivities reach 99 % GVL, 80 % ML, and 76 % MP under optimal conditions. • Catalytic performance depends on acidic and metallic sites, not surface area. This work aims to illustrate the benefits of continuous flow production in controlling process selectivity, using levulinic acid alkylation/hydrogenation as a model reaction. A novel catalyst composed of Ru nanoparticles, supported on hydrochar and functionalized with Brønsted acid sites, was synthesized. X-ray Photoelectron Spectroscopy (XPS) analysis of the catalysts revealed that O 1s species were responsible for Ru dispersion, contributing to the binding of –SO 3 H and –PO 3 H 2 ; however, C 1s species played a more dominant role in the latter process. The results demonstrated that the –SO 3 H and –PO 3 H 2 functional groups promote the formation of esterification products. The maximum selectivities achieved were 99 %, 80 %, and 76 % for γ-valerolactone, methyl levulinate and methyl pentanoate, respectively, with near complete conversion in each case at different times on stream in the flow process. The flow system operated within a temperature range of 210–290 °C and a hydrogen pressure range of 10–70 bar. Optimization of the continuous flow parameters enabled a more precise understanding of the reaction mechanism compared to existing literature.