Inhibition of Hydrogen Peroxide Decomposition by Adsorbed Halides: A DFT Study

The direct synthesis of H₂O₂ (DSHP) from H₂ and O₂ offers a “greener”, single-pot alternative to the current industrial-scale anthraquinone process for H₂O₂ production. An optimal DSHP catalyst must maintain high rates and selectivity at industrially relevant H₂O₂ concentrations. However, catalysts active for the DSHP generally also show activity for H₂O₂ decomposition reactions, limiting H₂O₂ yields.¹ This problem is avoided in the anthraquinone process, as the hydrogenation and oxidation steps are separated – avoiding contact of H₂O₂ produced with the hydrogenation catalyst.

Pd is the most widely studied catalyst for the DSHP, and one strategy to quench the undesired H₂O₂ decomposition reactions on Pd is to add acids and halides to the reaction medium.² Some proposed actions of the halide include blockage of coordinatively unsaturated Pd sites³ and/or prevention of O-O bond cleavage.¹ We utilize density functional theory (DFT) calculations to further probe the role of halides on the H₂O₂ decomposition reaction mechanism on Pd. This presentation will focus on the stability of reaction intermediates and energetics of select elementary steps in the presence of adsorbed halides. The results are discussed in the context of the experimentally observed trends for halide inhibition of H₂O₂ decomposition on Pd.⁴

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