Direct Epoxidation Of Prop Ylene Over Nano Gold Catalysts

One step synthesis of propylene oxide (PO) is a environmental friendly and more ecnomic process, which has attractd much attention in recent years. Nano-sized gold catalysts prepared by the deposition-precipitation method have advantages such as highly dispersed Au particles, which is beneficial to the reaction. High PO selectivity could be obtained on the gold catalysts, however, improvement of propylene conversion over these catalysts still needs further investigation.In this work, nano-sized gold catalysts supported on titanosilicate (TS-1) were synthesized and tested for dierect propylene epoxidation in the presence of H2and O2mixture. Modification of the TS-1support and promotion of gold catalysts were employed to improve the catalytic performance. The detailed contents are as follows:1.The effects of Ga modification on the catalytic performance Au/TS-1catalystsTitanium silicalite was synthesized using a conventional hydrothermal mathod. he incorporation of Ti(IV) into the framework was evidenced by UV-Vis spectroscopy. XRD showed that gallium was incorported into the struture of the TS-1. NH3-TPD show that the characterization of the acid strength of catalyst with the incorporation of Ga decreased. And the desorption of NH3peak area with Ga adding quantity can be increased, illustrate the catalyst surface acid sites showed increasing trend of number. The activity of propylene epoxidation was increased by using gold catalysts supported on Ga-modified TS-1.The Ga-modification promoted C3H6conversion from1.8to2.7%and PO selectivity from86.2%to91.9%, which may be due to the fine dispersion of Au particles and a ligand effect resulted from the change of the microstructure of the TS-1support.2. The effects of various promoters on the catalytic performance of Au/TS-1catalysts:Gold catalysts were modified with La, Pr, Zr, Co, also with TS-1treated with hydrazine hydrate, NaOH and NH3. It was found that the addition of La, Pr, Zr and Co suppressed the catalytic activity. For the N2H4treated catalysts, it was found that although the conversion of propylene decreased but the PO selectivity increased compared to the untreated samples.