Direct Propylene Epoxidation over RuO2–CuO–NaCl–TeO2–MnOx/SiO2 Catalysts: Optimized Operating Conditions and Catalyst Characterization

Abstract

Multimetallic catalysts of RuO2–CuO–NaCl–TeO2–MnOx supported on SiO2 were investigated for the direct-gas-phase epoxidation of propylene to propylene oxide (PO) using molecular oxygen under atmospheric pressure. Four operating variables (reactor temperature, O2 to propylene feed gas volume ratio, reactants to carrier gas volume ratio, and total feed gas flow rate) were studied using the Box–Behnken design, which enabled the achievement of a relatively high PO formation rate at 1507 gPO h–1 kgcat–1 with PO selectivity of 25.3% and propylene conversion of 5.9% at 1 h of time on stream. The optimized conditions were a reactor temperature of 297 °C, a O2/C3H6 ratio of 11.95, a (O2 + C3H6)/He ratio of 0.24, and a total feed gas flow rate of 36 cm3 min–1. The physical and chemical properties were characterized using various techniques that revealed that the crystallinity of RuO2 and CuO, the close proximity of RuO2 and CuO, and the surface’s acidity are crucial for PO production. NaCl plays a key role in reducing CO2 combustion. TeO2 and MnOx enhanced the active sites that facilitate PO production.