Gas Phase Epoxidation Of3,3,3-Trifluoropropylene Over Au Catalysts

3,3,3-trifluropropylene oxide(TFPO) is a very important intermediate in fluorochemical industry. Currently, the synthesis of TFPO exclusively goes through liquid phase reactions. Such routes have disadvantages such as complicated processes, waste production and difficulty in products separation. Compared to the liquid phase reaction, gas phase epoxidation of3,3,3-trifluoropropylene (TFP) is more appealing because of its high atomic efficiency, easy product separation and being environmentally benign. However, the catalytic activity of gas pahse epoxidation of TFP is usually low, thus makes it difficult to be industrialized and a challenging task.Few works have been reported in literature for gas phase epoxidation of TFP. In this thesis, a series of Au/Cu-TiO2and Au/TS-1catalysts were prepared and tested for TFP gas phase epoxidation. These catalysts were characterized by various techniques such as BET, ICP-AES, XRD, HTEM, NH3-TPD, H2-TPR and XPS, by which proper correlation between the catalyst properties and the catalytic behaviors was established. The detailed contents of the work are as follows:1.Gas phase epoxidation of TFP was conducted on a series of Au/Cu-TiO2catalysts with N2O as the oxidant.A series of Cu-TiO2support and the supported Au catalysts were prepared using an impregnation method and the deposition-precipitation method (DP) respectively. These catalysts were tested for TFP gas epoxidation with N2O as the oxidant. It was found that these catalysts were very selective for this reaction. The best catalytic performance was obtained on a catalyst containing4.6wt.%of Au and0.9wt.%of Cu (4.6Au/0.9Cu-TiO2), with a steady state3,3,3-trifluoropropylene oxide (TFPO) formation rate of72.4gTFPO h-1kgcat-1, which was much higher than that on a 2.1Au/TiO2catalyst (22.1gTFPO h-1kgcat-1).The enhancement was attributed to the higher Au content in the Cu-promoted catalyst and small Au particle size, and more importantly to the complicated synergy between the Au-Cu-TiO2interaction which might be the active sites for epoxidation. Also, high selectivity to TFPO up to88%was obtained on the Cu-promoted catalyst, due to the proper electronic structure induced by the interaction between Au and low valent Cu species. On the other hand, catalyst deactivation was due to the significant growth of Au particles and loss of Au-Cu-TiO2interface because of the segregation of Cu species during the reaction.2. Gas phase epoxidation of TFP was investigated on Au/TS-1catalysts with O2as the oxidant.TS-1support was synthesized by a hydrothermal method and various Au/TS-1catalysts were prepared using the deposition-precipitation method. It was found that the promotion of alkali metals in the catalysts such as K and Cs were beneficial for the improvement of catalytic performance. An intial TFP conversion of1.54%was obtained on a0.25Au/0.17Cs-TS-1catalyst (corresponding to a TFPO formation rate of31.4gTFPO-1·h-1·kgcat-1), which was much higher than that on the umpromoted0.78Au/TS-1catalyst (0.32%, corresponding to a TFPO formation rate of6.8gTFPO-1·h-1·kgcat-1). However, the catalysts promoted with alkali earth metals were not helpful to the improvement of the activity. The suppressed performance on the alkali earth metal-promoted catalyst might be due to the higher Au loadings and larger Au particles in these catalysts compared to the umpromoted catalyst, which consequently inhibited the activity.