Core–shell Cu@SiO₂/SiO₂ catalyst for 1,6-hexanediol dehydrogenation to ε-caprolactone: High activity and stability from core–shell nanostructure

The gas-phase dehydrogenation of 1,6-hexanediol (1,6-HDO) to ε-caprolactone (ε-CL) over the high-performance Cu-based catalysts is highly desirable, but with grand challenges, because the Cu nanoparticles (NPs) are easy to be sintered with the low Hüttig temperature (< 150 °C vs. > 250 °C of reaction temperature). Herein, we report a highly efficient silica-encapsulated nano-Cu catalyst (Cu@SiO₂/SiO₂) prepared via a complexation–impregnation method for the dehydrogenation of 1,6-HDO, exhibiting a 1,6-HDO conversion of 95.3% and ε-CL selectivity of 80.0% at 270 °C. The catalyst also has the outstanding thermal stability (without sintering up to 270 °C for 100 h on stream), which can be attributed to the effective encapsulation of the SiO₂ shell. In addition, the reaction network of 1,6-HDO dehydrogenation is proved. Finally, the pyridine-diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and in-situ X-ray photoelectron spectroscopy (XPS) reveal that the Cu⁰ species favor the conversion of 1,6-HDO to ε-CL. The synergistic effect of Cu⁺ and Cu⁰ benefits the conversion of ε-CL to 2-methylcyclopentanone (2-MCPN). This study is beneficial for designing the high-performance Cu-based catalysts for 1,6-HDO to ε-CL, understanding the reaction network of 1,6-HDO dehydrogenation over the Cu-based catalysts, and offering a strong foundation for the large-scale production of ε-CL.