Effect of low hydrogen to palladium molar ratios in the direct synthesis of H₂O₂ in water in a trickle bed reactor

Application of a trickle bed reactor (TBR) renders a very compact solution to carry out direct synthesis of hydrogen peroxide in water over a carbon supported palladium. The laboratory scale reactor was filled with silica particles (50–70 mesh) physically mixed with 37.5 to 75 mg of 5%Pd/C particles. The reaction conditions applied were 15 °C, 15–28 barg, 0.5 to 6 mL min−1 of liquid and 4.0–4.5 mL min−1 of gas flowrate (86.7/11/2.23 mol% of CO2/O2/H2). Thus, we demonstrated that the ratio between H2 and Pd is one of the key factors to achieve optimized, higher yields of hydrogen peroxide. Consequently, low H2 concentrations lead to low productivities. One of the least studied parameters, addressed here, is the ratio between the bed filling (SiO2) and the catalyst; i.e. the active catalytic species dilution effect. In short, it was found that when the amount of Pd was reduced below 0.094 mg Pd cm−3 SiO2 the highest productivity of H2O2 could be achieved. The selectivity obtained were between 5.3 and 38.0%, respectively, corresponding to turn-over-frequencies (TOF) ranging from 65 to 921 mmol H2O2 gPd−1 h−1.