The catalytic performance of RuO2-CuO/SiO2-based materials for the direct gas-phase epoxidation of propylene using molecular oxygen at atmospheric pressure was investigated as a function of the Ru/Cu weight ratio and the addition of NaCl, TeO2, Cs2O, or TiO2. The best performing catalysts were then assessed for stability. Doping with NaCl delivered the highest PO yield, but its catalytic activity dropped quickly within a few hours due to the loss of chloride content. The same catalyst doped instead with TeO2, Cs2O, or TiO2 could maintain stable catalytic performance for 6 h. However, the addition of TeO2 presented the best improvement in terms of PO selectivity. Further optimization of PO selectivity for the RuO2-CuO-TeO2/SiO2 catalyst system was accomplished by varying reactor temperature and total feed gas flow rate. The highest PO selectivity could be achieved at 47% (255 g(PO) h(-1) kg(cat) (-1), 0.35% propylene conversion). The time-on-stream test revealed excellent catalytic stability within the 12 h of test period without any deactivation. Graphical Abstract [GRAPHICS] .