Support Effects on Pd and Au Catalysts for Direct Synthesis of Hydrogen Peroxide

The direct synthesis of hydrogen peroxide (H₂O₂) from H₂ and O₂ offers a cleaner, safer, and more cost-effective alternative to the traditional anthraquinone process used industrially. However, it remains challenging to design catalysts that achieve both high H₂O₂ formation rates and selectivity against water and remain stable under reaction conditions. Palladium catalysts readily activate H₂ and promote high formation rates, while gold catalysts stabilize O-O bonds to show high H₂O₂ selectivity. Bimetallic Pd₁Au_x catalysts balance the high reactivity and selectivity of Pd and Au respectively by preferentially stabilizing transition states and reactive intermediates. Yet, the role of catalyst support in achieving this balance is still not well understood. Supports can influence catalyst behavior by directly participating in the reaction through surface functional groups or acid–base properties, introducing new active sites, or stabilizing and restructuring the metal surface through strong metal–support interactions.

In this work, we focus on monometallic Pd and Au catalysts to isolate the effects of the support, before applying these insights to bimetallic catalysts. This work aims to answer how the support alters the surface structure of ~2 nm Pd and Au catalysts which in turn influences steady-state kinetics and mechanism, including H₂O₂ selectivity, and the long-term stability of Pd and Au catalysts.

To address these objectives, ~2 nm Pd and Au nanoparticles were synthesized on Al₂O₃, SiO₂, and TiO₂ supports using strong electrostatic adsorption. The catalysts were characterized by transmission electron microscopy to measure particle size and dispersion, CO chemisorption and infrared spectroscopy of adsorbed CO to quantify the number of active surface sites and track structural changes under reductive and oxidative conditions. Reactor studies using a continuous flow trickle-bed system were used to measure steady-state H₂O₂ formation rates, selectivity, activation enthalpies, and pressure dependencies with respect to H₂ and O₂ to elucidate changes to the kinetics and reaction mechanism.

These studies allow us to evaluate how supports influence catalyst structure, kinetics, and stability, providing insights that can guide the design of Pd and Au catalysts for the direct synthesis of hydrogen peroxide.