Continuous H2O2 direct synthesis over PdAu catalysts

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 °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 H2/O2 ratio (2/18 and 4/16) in the gas feed, has been studied, by independent variations. The highest H2/O2 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 H2/O2 ratio is used. A selectivity up to 90% has been measured on PdAu-ZS with the higher H2/O2 ratio and larger liquid flow rates. The maximum production rate measured is 6 μmol/min (i.e. a productivity 0.18 mol H2O2 gPd−1 h−1) with 1 ml/min liquid flow rate and 2.7 ml/min gas flow rate again on PdAu-ZS.

► A trickle bed reactor was successfully developed for H2O2 direct synthesis.
► PdAu-ZS catalyst shows better activity compared to PdAu-CeS catalyst.
► H2/O2 ratio in the gas has an important role on catalyst activity.
► Selectivity of 90% was achieved with PdAu-ZS catalyst.