Amine-promoted Ru1/Fe3O4 encapsulated in hollow periodic mesoporousorganosilica sphere as a highly selective and stable catalyst for aqueous levulinic acid hydrogenation

Abstract

It is of great importance to develop selective and stable metal catalysts for the aqueous levulinic acid hydrogenation, yet challenging. Herein, we report a yolk-structured sing atom catalyst (SAC) with amine-modified Ru1/Fe3O4 core and periodic mesoporousorganosilica (PMO) shell, synthesized by a core–shell dual stabilization strategy. The Ru single atoms (0.76 wt%) are inserted into the oxygen vacancies of spheric Fe3O4, and stabilized by the amine groups from 1,6-hexanediamine. The hollow PMO sphere is hydrophobic, that affords a strong barrier for interior Ru1/Fe3O4 core, and the shell mesopore (4.2 nm) along with the cavity enhances the porosity of the resultant catalyst. As expected, the amine-promoted Ru1/Fe3O4 core in the hollow PMO shell (denoted as N-Ru1/Fe3O4@void@PMO), proves to be highly selective and stable for the aqueous levulinic acid (LA) hydrogenation under harsh conditions (pH ≈ 1), giving γ-valerolactone (GVL), a biomass-derived platform molecule with wide applications in the preparation of renewable chemicals and liquid transportation fuels. The elaborately fabricated catalyst is highly efficient, delivering 98.9% of selectivity to GVL and 99.0% of LA conversion in acidic water. And a high turnover frequency of 1084 h−1 is achieved and this catalyst can be cycled 7 times without apparent drop of GVL yield and LA conversion. The amine-stabilized Ru single sites, acid-resistant Fe3O4 circled by the hydrophobic shell, and the enhanced porosity of catalyst, are responsible for the excellent catalytic performance of N-Ru1/Fe3O4@void@PMO in acidic water.