Unlocking the Acidity‐Reactivity Correlation of Metal(IV)‐Doped Silica Nanotubes in the Conversion of Ethyl Levulinate

Metal-doped hollow silica nanotubes (M-NT, where M = Ti, Zr, Hf) were successfully synthesized via a straightforward impregnation of pristine hollow silica nanotubes with M-acetylacetonate solutions. After their characterization, the materials were tested as heterogeneous catalysts for the conversion of ethyl levulinate (EL) into γ-valerolactone (GVL) revealing highly promising activity for the target reaction. Special emphasis was given on disclosing the influence of the nature of the acid sites (Lewis or Bronsted) and their strength on the catalytic performances. Ammonia temperature programmed desorption (NH3-TPD), 31P solid-state nuclear magnetic resonance (31P-ssNMR) of trimethylphosphine and FT-IR of adsorbed ammonia, were the key techniques to evaluate the structure–activity correlation. The best solid exceeds the activity of other reference catalysts reported in the literature and tested under similar reaction conditions. The efficient recyclability of the best catalyst of the series was evaluated as well. The low E-factor obtained further confirmed the overall sustainability of the process.