Synthesis of a novel super-microporous layered material and its catalytic application in the vapor-phase Beckmann rearrangement of cyclohexanone oxime

A novel well-ordered super-microporous layered material, silica-pillared niobic acid, was synthesized by a guest-exchange route and structurally characterized by powder X-ray diffraction (XRD), infrared absorption spectroscopy (IR), thermogravimetric and differential thermal analysis (TG/DTA), transmission electron micrographs (TEM), nitrogen adsorption method and ammonia-temperature-programmed desorption (NH₃-TPD). The obtained silica-pillared layered niobic acid had a supergallery of 1.78 nm, a large BET surface area of 250 m² g⁻¹, and a high thermal stability exceeding 973 K.The pillared layered material was also found to be an efficient solid acid catalyst for the vapor-phase Beckmann rearrangement of cyclohexanone oxime. When 1-hexanol was fed with cyclohexanone oxime, this solid catalyst exhibited a 100% conversion of the oxime with a selectivity of ε-caprolactam beyond 85% at a reaction temperature of 613 K and a WHSV of 0.17 h⁻¹ in terms of cyclohexanone oxime, and there was no significant change of the conversion and selectivity within 6 h.