Influence of Na+ on the synthesis of silicalite-1 catalysts for use in the vapor phase Beckmann rearrangement of cyclohexanone oxime

Abstract

Silicalite-1 was hydrothermally synthesized in the presence of different concentrations of Na + using tetrapropylammonium hydroxide (TPAOH) as a template. The synthesis was followed by a base treatment. The silicalite-1samples were characterized using X-ray diffraction, scanning electron microscopy, N 2 adsorption, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and NH 3 temperature-programmed desorption. The samples were used as catalysts for the vapor phase Beckmann rearrangement of cyclohexanone oxime. During the synthesis, the sodium ions were incorporated onto the silicalite-1 crystals, but were then removed by the base treatment. All the catalysts exhibited nearly complete conversion of cyclohexanone oxime to ε-caprolactam with selectivities grater than 95%. Addition of less than 2.5 mol-% Na + (relative to TPAOH) did not influence the catalytic properties. However, for Na + concentrations≥5 mol-%, the particle sizes of silicalite-1 increased and the catalytic activities decreased, which can be attributed to carbon deposition. The results in this work are of great importance for the polymer industry.

Surface silanol sites in mesoporous MFI zeolites for catalytic Beckmann rearrangement

“…This size difference is attributed to the effect of alkali metal ions, which could promote zeolite particle growth. 46,47 The particle diameters in both Bz-ac and Bz-af are sufficiently large to contain numerous micropores ( D = 0.55 nm) when measured through any of the crystallographic axes, confirming the solely microporous texture indicated by the adsorption isotherms. When treated with an NH 3 /NH 4 + buffer solution, as in the work of Heitmann et al , 7 the Bz-ac and Bz-af zeolites underwent a 10–15% loss of BET surface area.…”

Hydrothermal Synthesis of High Crystalline Silicalite from Rice Husk Ash

“…It contains two intersecting channel systems composed of 10-membered ring straight and sinusoidal channels with a unique pore structure dimension of 0.54-0.56 nm. According to a variety of its useful properties such as strong hydrophobicity, excellent shape selectivity, good catalytic activity, and high thermal stability, hence, it has been widely used in industrial applications for adsorption [1], catalysis [2], and gas and liquid separation [3,4].…”