Yolk-shell Co catalysts with controlled nanoparticle/single-atom ratio for aqueous levulinic acid hydrogenation to gamma-valerolactone

Precise and facile tailoring of metal nanoparticle/single-atom ratio to optimize the catalytic hydrogenation activity and durability is important yet challenging, owing to the lack of efficient synthetic methodology. Herein, we report a brand-new Co catalyst with precisely tailored Co NP/Co SA ratio encapsulated into a hollow carbon sphere, skillfully fabricated by stepwise coating of bimetallic Zn/Co zeolitic imidazole frameworks with silica and 8-quinolinol modified chitosan before pyrolysis and acid washing. The transformation of the target catalyst and the tailoring of Co NP/Co SA ratio are well investigated by various characterization techniques including TEM, aberration-corrected scanning TEM (AC-STEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and X-ray absorption fine structure (XAFS), etc. It is found that the yolk-shell structured Co catalyst integrated with nearly equivalent nanoparticles and sing-atoms are highly active and stable towards aqueous levulinic acid (LA) hydrogenation to.-valerolactone (GVL). Combined with H-2-TPD and LA adsorbed FT-IR investigations, it is revealed that the superior activity originates from the synergism of Co nanoparticles and single-atoms, since H-2 dissociation and C=O adsorption are facilitated by Co nanoparticles and single-atoms, respectively, leading to a lowered energy barrier during the hydrogenation reaction. This study will shed light on the precise tailoring of metal nanoparticle/single-atom ratio and also provides a new insight into the development of highly efficient non-noble metal catalysts for sustainable biomass conversion.