Direct synthesis of $H_{2}O_{2}$ in continuous flow: an operando XAS study on palladium catalysts

Direct synthesis of hydrogen peroxide ($H_{2}O_{2}$) over Pd-TiO$_2$ was investigated in a continuous flow reactor operating at ambient temperature and elevated pressure. Operando X-ray Absorption Spectroscopy (XAS) and on-line flow injection analysis for photometric quantification of $H_{2}O_{2}$ were used to assess catalyst performance under various experimental parameters, including flow rate and reactant ratio ($H_{2}:O_{2}$) in the liquid phase. Variations in oxidation state and local Pd structure provided insight into the reaction mechanism of direct $H_{2}O_{2}$ synthesis, indicating oxygen adsorbed on the surface of Pd nanoparticles and hydrogen reacting from the bulk PdH$_x$ (α-phase). The results obtained allowed proposal of a mechanism for direct $H_{2}O_{2}$ synthesis, which facilitates knowledge-based catalyst design, optimization and improved efficiency for this challenging chemical process