Direct Synthesis of Hydrogen Peroxide from Hydrogen and Oxygen Over Size-Controlled Palladium Nanocube Catalysts

Size-controlled palladium (Pd) nanocubes were prepared by colloidal methods in the presence of different surface-stabilizing agents, polyvinylpyrrolidone (PVP) and tetradecyltrimethylammonium bromide (TTAB). Average particle sizes of PVP-stabilized Pd nanocubes were 12, 15, and 18 nm (denoted as PVP-XPC (X = 12, 15, and 18)). In case of TTAB-stabilized Pd nanocubes, average particle sizes were 18, 25, and 33 nm (denoted as TTAB-XPC (X = 18, 25, and 33)). The Pd nanocubes supported on gamma-Al2O3 were applied to the direct synthesis of hydrogen peroxide from hydrogen and oxygen. Conversion of hydrogen and selectivity for hydrogen peroxide increased with decreasing size of Pd nanocubes. The effect of stabilizing agent was also investigated by comparing the catalytic activity of Pd nanocubes prepared with different stabilizing agent. TTAB-stabilized Pd nanocubes showed better catalytic activity than PVP-stabilized Pd nanocubes. FT-IR and TGA analyses revealed that strong C=O and C-N chemical bonding species remained on the PVP-stabilized Pd nanocubes, while only a small amount of alkyl species remained on the TTAB-stabilized Pd nanocubes. This different catalytic activity of Pd nanocubes was due to the difference in remaining chemical species on the Pd surface between PVP- and TTAB-stabilized nanocubes.