H2O2 direct synthesis over two bimetallic, palladium-gold catalysts based on sulfated ceria (PdAu-CeS) and on sulfated zirconia (PdAu-ZS) has been studied in a continuous, trickle-bed reactor, at -10 degrees C and 10 bar. Three different liquid flow rates and seven different gas flow rates were used. The combined effect of liquid and gas flow rates, with two different H-2/O-2 ratio (2/18 and 4/16) in the gas feed, has been studied, by independent variations. The highest H-2/O-2 ratio always increases production rate and selectivity. In the case of 4/16 ratio, PdAu-CeS catalyst shows an enhancement in selectivity only, while the increase in H2O2 production rate is not significant compared to the 2/18 ratio case. PdAu-ZS catalyst shows a remarkable gain in both selectivity and production rate when the 4/16 ratio in gas feeding is used, outperforming the PdAu-CeS catalyst. The enhancement of the catalytic activity is more pronounced in the case of PdAu-ZS, compared to PdAu-CeS, when the highest H-2/O-2 ratio is used. A selectivity up to 90% has been measured on PdAu-ZS with the higher H2O2 ratio and larger liquid flow rates. The maximum production rate measured is 6 mu mol/min (i.e. a productivity 0.18 mol H2O2 g(pd)(-1) h(-1)) with 1 ml/min liquid flow rate and 2.7 ml/min gas flow rate again on PdAu-ZS. (C) 2011 Elsevier B.V. All rights reserved.