Synthesis of Mesoporous Titanium Silicalite-1 with High Stability in Cyclohexanone Ammoximation

Mesoporous titanium silicalite-1(TS-1)was hydrothermally synthesized with the addition of triethanolamine(TEA)in the conventional process, and used in the cyclohexanone ammoximation in a continuous slurry reactor. The as-prepared TS-1 was characterized with X-ray diffraction(XRD), scanning electron microcopy(SEM), N_2 adsorption-desorption, Fourier transform infrared(FT-IR)spectroscopy, UV-Visible(UV-Vis)diffuse reflectance spectra and UV Raman spectroscopy. The results indicated that the addition of TEA resulted in the formation of mesopores and the slight increase of framework titanium in TS-1. TS-1 synthesized with the addition of TEA exhibited a higher stability in the cyclohexanone ammoximation than that without the addition of TEA, attributing to the increase of mesopore volumes and the slight increase of the framework titanium in TS-1. However, when the addition of TEA was up to TEA/SiO_2 ratio of 0.24, the crystallinity and framework titanium of TS-1 decreased markedly, and the average crystal sizes of TS-1 increased, with the catalyst stability becoming poor.

Effect of sodium ions in synthesis of titanium silicalite-1 on its catalytic performance for cyclohexanone ammoximation

Titanium silicalite-1 （TS-1） has been hydrothermally synthesized with tetrapropylammonium hydroxide （TPAOH） as the template in the presence of various amounts of Na＋, characterized by inductively coupled plasma, X-ray diffraction, scanning electron microscope, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and ultro-violet-visible spectroscopy and studied in cyclohexanone ammoximation. The characterization results show that with the increase of Na＋ concentration in the synthesis, both the crystal sizes of TS- land extra framework Ti increase but framework Ti decreases. The addition of Na＋ below 3 mol-% of TPAOH in the synthesis does not influence the catalytic properties with above 98% conversion of cyclohexanone and 99.5% selectivity to cyclohexanone oxime. However, at the concentrations of Na＋≥3mol-% of TPAOH in the synthesis, the catalysts are deactivated faster with the increase of Na＋ addition, which can be attributed to more high molecular weight byproducts deposited in the large TS-1 particles and the loss of the frame-work titanium. The results of this work are of great importance for the industry.

Seed-induced synthesis of small-crystal TS-1 using ammonia as alkali source

Small-crystal TS-1 was synthesized via a seed-induced approach using ammonia as the alkali source and tetrapropylammonium bromide as an auxiliary structure-directing agent. The TS-1 samples were characterized using X-ray diffraction, N2 adsorption-desorption, Fourier-transform infrared spectroscopy, inductively coupled plasma atomic emission spectroscopy, scanning electron microscopy, and ultraviolet-visible spectroscopy. The use of the colloidal seed reduced the crystal size, and an appropriate amount of silicalite-1 seed assisted Ti incorporation into the TS-1 framework. This method reduces the cost of TS- 1 synthesis because a significantly smaller amount of tetrapropylammonium hydroxide is used. The catalytic performance of the synthesized small-crystal TS-1 samples in cyclohexanone ammoximation was better than that of bulk TS-1 as a result of improved diffusion and a larger number of active tetrahedral Ti centers.