Construction of Oxygen Vacancy-Rich TiO 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 with different oxygen vacancy concentrations was prepared by chemical reduction using NaBH. The oxygen vacancy on TiO surface, presented as Ti sites, substantially enhances the adsorption and activation of NH, which are demonstrated as the key steps in ammonolysis. Owing to the synergistic effect of Ti and Ti 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 had a more favorable adsorption energy compared to those on intact TiO, which is in good agreement with the experimental results.