One-step synthesis of ε-caprolactam from cyclohexane and nitrosyl sulfuric acid catalyzed by VPO supported transition metal composites

A series of transition metal-doped VPO composite catalysts were prepared by impregnating method, and were employed to catalyze reaction of cyclohexane with nitrosyl sulfuric acid in the presence of fuming sulfuric acid. To our delight, ε-caprolactam was directly obtained from such one-step catalytic process. It was found that Mn/AlVPO gave the best results with 9.8% of conversion and 72.9% of selectivity to ε-caprolactam among present composite catalysts. While the conversion and selectivity are not high at this time to be commercially viable, this discovery establishes a potential new one-step process for making ε-caprolactam from cyclohexane.