Multimetallic catalysts of RuO2–CuO–Cs2O–TiO2/SiO2 for direct gas-phase epoxidation of propylene to propylene oxide†
RuO2–CuO/SiO2 catalysts doped with Cs2O and TiO2 were investigated for the direct gas phase epoxidation of propylene to propylene oxide (PO) using molecular oxygen under atmospheric pressure. The optimal catalyst was achieved at Ru/Cu/Cs/Ti = 8.3/4.2/0.6/0.8 by weight and total metal loading of 21 wt% on SiO2 support. NH3 and CO2 temperature programmed desorption measurements of RuO2–CuO/SiO2 catalyst modified with Cs2O showed that the surface's acidity decreased, resulting in enhanced PO selectivity. The addition of TiO2 increased the PO formation rate by promoting the synergy effect between RuO2 and CuO. Using the Box–Behnken design of experiments on the RuO2–CuO–Cs2O–TiO2/SiO2 catalyst, an extraordinarily high optimal PO formation rate of 3015 gPO h−1 kgcat−1 was obtained with a feed comprised of O2/C3H6 at a volume ratio of 3.1 and (O2 + C3H6)/He at a volume ratio of 0.26, all at 272 °C and 34 cm3 min−1. To the knowledge of the authors, this is the highest PO formation rate ever reported for direct propylene epoxidation via O2.