Towards rational design of core–shell catalytic nanoreactor with high performance catalytic hydrogenation of levulinic acid

We have described herein the synthesis and characterization of a uniquely designed mesoporous silica shell@Pd nanoparticle tethered amine functionalized silica core catalyst and its catalytic properties in the hydrogenation of levulinic acid, a key platform molecule in many biorefinery schemes, into γ-valerolactone, using formic acid as a sustainable H2 source. Monodispersed silica core particles (∼300 nm in diameter) were prepared and further functionalized by amine groups and then the in situ loading of Pd nanoparticles was carried out. Pd0-NPs are sandwiched between the nonporous silica core and the mesoporous silica shell, leading to the exceptional stability of the catalyst. The nanostructured material was thoroughly characterised by means of powder XRD patterns, N2 sorption, FE-SEM, UHR-TEM, TG-DTA, and XPS analysis. Our core–shell nanostructure catalyst encapsulated with Pd nanoparticles exhibited a significant increase in catalytic activity and excellent selectivity towards γ-valerolactone (99%) compared with control catalysts for levulinic acid hydrogenation, including Pd@C and Pd@SiO2 (without a mesoporous SiO2 shell). Our results suggest that the core–shell silica based nanocatalyst offers tremendous recyclability (up to the 10th catalytic run with consistent conversion and selectivity of γ-valerolactone), stability (no leaching of Pd and structure collapsing) and no sign of deactivation.