Construction of Oxygen Vacancy-Rich TiO 2 Nanocrystals for Boosting the Ammonolysis of Caprolactam to 6-Aminocapronitrile.

Hexamethylene diamine, an important chemical intermediate for polyamides, can be synthesized through the two-step route of caprolactam (CPL) ammonolysis to 6-aminocapronitrile (ACN), followed by hydrogenation. This method has received increasing attention from academia and industry. However, studies on the catalyst structure-performance correlation in CPL ammonolysis are still sporadic. In this work, a series of anatase TiO 2 with different oxygen vacancy concentrations was prepared by chemical reduction using NaBH 4 . The oxygen vacancy on TiO 2 surface, presented as Ti 3+ sites, substantially enhances the adsorption and activation of NH 3 , which are demonstrated as the key steps in ammonolysis. Owing to the synergistic effect of Ti 3+ and Ti 4+ species, the CPL conversion rate and ACN selectivity of 85 and 97%, respectively, are achieved within 250 h. Density functional theory calculations showed that the intermediates on oxygen vacancy-rich TiO 2 had a more favorable adsorption energy compared to those on intact TiO 2 , which is in good agreement with the experimental results.