Influence of Br − and Na + in synthesis of Silicalite-1 on catalytic performance in vapor phase Beckmann rearrangement of cyclohexanone oxime

Abstract

Silicalite-1 was hydrothermally synthesized with tetrapropylammonium hydroxide (TPAOH) as the template in the presence of various Br − and Na + concentrations, characterized by XRD, SEM, BET, XPS, FT-IR and NH 3-TPD and studied in the vapor phase Beckmann rearrangement of cyclohexanone oxime. The characterization results show that the crystal sizes of Silicalite-1 increase with the increase of Na + concentrations in the synthesis; Na + is combined in the Silicalite-1 crystals, but removed by a base treatment. The base treated catalysts exhibit nearly complete conversion of cyclohexanone oxime with above 95% selectivity to ɛ-caprolactam. Catalysts with the addition of up to 20 mol% Br − relative to TPAOH without Na + in the synthesis do not influence the physical and chemical as well as the catalytic properties. The addition of Na + below 2.5 mol% of TPAOH do not influence the catalytic properties either. However, at the concentrations of Na + ≥ 5 mol% of TPAOH in the synthesis, the catalysts deactivate faster with the increase of Na + contents, which is attributed to more carbon deposition in the larger Silicalite-1 particles, determined by TGA. The results of this work are of great importance for the industry.