Multimetallic catalysts of RuO2–CuO–Cs2O–TiO2/SiO2 for direct gas-phase epoxidation of propylene to propylene oxide

Abstract

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 g_PO h⁻¹ kg_cat⁻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.