Direct production of H2O2 from H2 and O2 in a biphasic H2O/scCO2 system over a Pd/C catalyst: Optimization of reaction conditions

The direct synthesis of hydrogen peroxide has been achieved using only water as solvent in a semi-continuous stirred reactor system; this is a greener alternative over the traditional process using anthraquinone or the direct synthesis process using organic solvents (e.g. alcohols). The use of an inert co-solvent such as scCO2 is advisable due to safety issues. Moreover, the use of scCO2 presents additional advantages due to its acidification effect and the important enhancements it causes in the mass transfer coefficients for both the gas and the liquid phase when compared to N2. The catalyst used, a commercial 5 wt.% Pd/C, was especially active and amounts as low as 15 mg per 200 mL of reaction volume produced remarkable results with turnover frequencies after 2 h (TOF120) over 2 molH2O2 h−1 gcat−1. A maximum productivity of 0.84 mmolH2O2 min−10.84 mmolH2O2 min−1 in our system was obtained for the optimized conditions, obtaining selectivities around 60% and yields around 20%. A maximum concentration of 4.3% (w/v) H2O2 was obtained after 8 h. An on-line monitoring Raman technique was used for H2O2 quantification.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Improvement of the direct synthesis of H2O2 in water at high pressures without the use of organic solvents. ► In-depth study of the influence of mass transfer and kinetics in the three-phase reaction. ► CO2 enhances mass transfer over the use of N2.