Reaction mechanism of direct H2O2 synthesis from H2 and O2 over Pd/C catalyst in water with H+ and Br− ions

The direct synthesis of hydrogen peroxide using a combination of a hydrophobic solvent and water

The use of a hydrophobic solvent in combination with water leads to significant suppression of H₂O₂ degradation pathways over a AuPd/C catalyst.

How Does the Oxidation State of Palladium Surfaces Affect the Reactivity and Selectivity of Direct Synthesis of Hydrogen Peroxide from Hydrogen and Oxygen Gases? A Density Functional Study

Direct synthesis of H₂O₂ from H₂ and O₂ is an environmentally benign and atom economic process and as such is the ideal pathway in catalysis. However, currently no low-cost pathway of this kind of catalysis exists, although it would be an attractive alternative strategy to the common industrial anthraquinone method for H₂O₂ production. Metal-based catalysts are widely employed in such a direct synthesis process but often need to be oxidized, alloyed, or supplied with additives to make them selective. To understand the metal-oxidation state in heterogeneous catalysis, we studied the selective oxidation of hydrogen by molecular oxygen on Pd(111) and PdO(101) surfaces, leading to either H₂O₂ or H₂O products. Our results demonstrate, for the first time, that the oxidized PdO(101) surface clearly shows better performance and selectivity, as compared to the reduced Pd(111) one. The activation barrier on the oxidized Pd surface is ca. 0.2 eV lower than the one on the reduced Pd surface. On the oxidized surface, the H₂O₂ synthesis route is preferred, while, on the reduced surface, the H₂O route is predominant. The decomposition of H₂O₂ is also greatly inhibited on the oxidized surface. We analyzed the different pathways in detail through thermochemical cycles, which establishes that the oxidized surface shows weaker adsorption ability toward the reagents O₂ and H₂, the key intermediate OOH, and also the product H₂O₂ in comparison with the Pd(111) surface, which we believe affect the selectivity. The work presented here clearly shows that the oxidation state of metal surfaces is one of the most important factors that tunes the catalysis of a chemical reaction and can affect the selectivity and reaction patterns dramatically.

Enhancement of catalytic activity of Pd-PVP colloid for direct H2O2 synthesis from H2 and O2 in water with addition of 0.5 atom% Pt or Ir

Atomically dispersed Pt or Ir atoms enhance H₂O₂ and H₂O formation on Pd nano-particles leaving the H₂O₂ hydrogenation rate unchanged, while Ru, Rh, or Au atoms show little effect.

The use of modelling to understand the mechanism of hydrogen peroxide direct synthesis from batch, semibatch and continuous reactor points of view

Modelling is a powerful tool to understand the mechanism of H₂O₂ direct synthesis.

Catalysts for direct H2O2 synthesis taking advantage of the high H2 activating ability of Pt: kinetic characteristics of Pt catalysts and new additives for improving H2O2 selectivity

To develop efficient catalysts for the direct H₂O₂ synthesis from H₂ and O₂ by taking advantage of the high H₂ activating ability of Pt, kinetic studies of the H₂–O₂ reaction were performed using a Pt-PVP (polyvinylpyrrolidone) colloid and Pt supported on carbon (Pt/C) as catalysts, and new additives were explored.

The influence of catalyst amount and Pd loading on the H2O2 synthesis from hydrogen and oxygen

Direct synthesis of H₂O₂: structure sensitivity in H₂O₂ production and structure insensitivity in the H₂O production were proved with a Pd/K2621 catalyst.