Direct Epoxidation Of Propylene Over Modified Au/TS-1 Catalysts

Direct epoxidation of propylene over Au/TS-1 catalysts with hydrogen and oxygen is a environmental friendly and economic process, which has very important value. However, the C3H6 conversion is usually low on the Au/TS-1 system, therefore, the improvement of C3H6 conversion is vital to the commercialization. In this thesis, Au/TS-1 catalysts were prepared by a deposition-precipitation method and tested for direct propylene epoxidation. Modification of the TS-1 support and promotion of catalysts in the preparation process were carried out and their effects on the catalytic performance was investigated. The catalysts were characterized by X-ray power diffraction analysis (XRD), ultraviolet visible spectroscopy (UV-Vis), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscope (TEM) techniques. It is found that the modification of Au/TS-1 could greatly improve the catalyst activity.The detailed results are as follows:1. The effects of Sn modification on the catalytic performance Au/TS-1 catalystsTitanium silicalite (TS-1) was synthesized using a conventional hydrothermal method. The incorporation of Ti(IV) into the framework was evidenced by UV-Vis spectroscopy. The XRD and FTIR results showed that Sn was incorported into the TS-1 matrix during the synthesis process. The presence of Sn in the catalyst resulted in an increment of C3H6 concersion from 1.6 to 2.5% and PO selectivity from 87 to 90%, which may be due to a ligand effect.2. The effects of In promotion on the catalytic performance of Au/TS-1 catalystsA series of Au/TS-1 catalysts promoted with In were prepared and tested for direct propylene epoxidation. It was found that the gold loading and catalytic activity were enhanced by the addition of In. The TEM results showed that gold particles on the In modified catalysts were highly dispersed and the particle sizes were smaller compared to the unpromoted catalyst. The highest reactivity was obtained on a 0.57Au/0.4In-TS-1(100) catalyst, gaving a C3H6 conversion of 3.8% and a PO formation rate of 56 gpokgcat-1h-1 at the steady state, which is 1.8 times as high as that on the unpromoted 0.25Au/TS-1(100) catalyst (32 gpokgcat-1h-1). The improvement was ascribed to the increased Au capture efficiency by the addition of In in the catalyst.3. The effects of various promoters on the catalytic performance of Au/TS-1 catalystsAu/TS-1 catalysts were promoted with ammonium molybdate, chromium nitrate and chloroiridic acid. It was found that the addition of Mo and Cr resulted in a decline in catalytic activity, but a stable conversion of C3H6. Promotion of Ir greatly improved the activity and stability of the catalyst. It was believed that highly active and stable Au/TS-1 catalysts may be synthesized by optimization of the perparation conditions.