Reproducible preparation of Au/TS-1 with high reaction rate for gas phase epoxidation of propylene

A refined and reliable synthesis procedure for Au/TS-1(Si/Ti molar ratio ∼100) with high reaction rate for the direct gas phase epoxidation of propylene has been developed by studying the effects of pH of the gold slurry solution, mixing time, and preparation temperature for deposition precipitation (DP) of Au on TS-1 supports. Au/TS-1 catalysts prepared at optimal DP conditions (pH ∼ 7.3, mixing for 9.5 h, room temperature) showed an average PO rate ∼160gPOh-1kgCat-1 at 200 °C at 1 atm. A reproducibility better than ±10% was demonstrated by nine independent samples prepared at the same conditions. These are the highest rates yet reported at 200 °C. No visible gold particles were observed by the HRTEM analysis in the fresh Au/TS-1 with gold loading up to ∼0.1 wt%, indicating that the gold species were smaller than 1 nm. Additionally, the rate per gram of Au and the catalyst stability increased as the Au loading decreased, giving a maximum value of 500gPOh-1gAu-1, and Si/Ti molar ratios of ∼100 gave the highest rates.

The Au/TS-1 catalysts prepared at optimal DP conditions (pH of the gold slurry solution, the mixing time, and the preparation temperature) showed a PO rate ∼160gPOh-1kgCat-1, which is the highest PO rate at 200 °C yet reported. Instead of using TS-1 with high Ti content to increase the site density, diluted systems (low Au loading/low Ti loading) are recommended for preparing highly active Au/TS-1 for PO production.Figure optionsDownload high-quality image (94 K)Download as PowerPoint slideHighlights
► DP conditions were optimized to prepare highly active Au/TS-1 for the PO reaction.
► An average PO rate ∼160gPOh-1kgCat-1 at 200 °C was achieved.
► High gold atom efficiency at low gold loading suggests small gold clusters are more active for the PO reaction.
► Low Au loadings and Si/Ti molar ratios ∼100 are recommended for preparing highly active Au/TS-1 for PO production.