The Direct Gas-phase Epoxidation Of Propylene On Au/TS-1 Catalysts

Propylene oxide (PO) is a valuable chemical intermediate. At present, the industrial production of PO mainly includes the Chlorohydrin process and the Halcon process. The Chlorohydrin process produces large amount of chlorine-containing wastewater; while the Halcon process has the co-product problem. The direct propylene epoxidation with hydrogen and oxygen is a low energy-cost and environmental benign reaction, which attracts much attention in catalysis field.In this thesis, the direct propylene epoxidation on nano-sized gold catalysts in the presence of hydrogen and oxygen was investigated. Effects of various preparation conditions on the performance of Au/TS-1 catalysts were studied. Modification of TS-1 support and promotion of Au/TS-1 catalysts with various metal ions were employed to improve the catalytic performance, and the reaction kinetics on the 0.08Au-K/TS-1(100) catalyst was analyzed.Au/TS-1 catalysts have good stability and high PO selectivity (>90%). Various preparation conditions such as n(Si):n(Ti), HAuCl₄ concentration, precipitating agent, precipitating pH and drying conditions have great influences on the catalytic activity of the catalysts. Under the optimised conditions (C_hauCl4 =3 g/L, n(Si):n(Ti)=100, NaOH as precipitating agent, pH=7, drying under vacumm), a C₃H₆ conversion of 2.5% and a PO selectivity of 90% were obtained on the 0.15Au/TS-1(100) catalyst.A series of alkali metal or alkaline earth metal nitrates promoted Au/TS-1 catalysts were prepared using a deposition-precipitation method and tested for direct epoxidation of propylene in the presence of H₂ and O₂. Results indicate that the addition of alkali metal or alkaline earth metal can remarkably increase formation rate of propylene oxide (PO). PO formation rate on a 0.13Au/TS-1(100) catalyst was 25 g_Po/((h·kg_cat) while a KNO₃ promoted 0.08Au-K/TS-1(100) catalyst gave a PO formation rate of 44 g_Po/(h·kg_cat), which was almost 80% of enhancement. The enhancement is due to the smaller Au particles (1～2 nm) in the alkali metal nitrates promoted catalyst, compared to unpromoted one, whereas the improvement in alkaline earth metal nitrates promoted catalyst is due to increase in Au loading.We firstly prepared the nano-gold catalysts supported on the Ge(IV) modified TS-1 and tested the reaction. It is found that the epoxidation of propylene is remarkably enhanced on Au/Ge-TS-1(100) catalysts compared with the 0.13Au/TS-1(100) catalyst. The conversion of C₃H₆ was 4.0% and the selectivity of PO was 91% on the Au/0.04Ge-TS-1(100) (n(Ge):n(Ti)=0.04) catalyst. The 0.14Au/0.04Ge-TS-1(100) catalyst gave a PO formation rate of 66 g_po/(h·kg_cat), which was of almost two-fold enhancement.