(166c) 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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2.         Edwards
JK, Freakley SJ, Lewis RJ, Pritchard JC, Hutchings GJ. Advances in the direct
synthesis of hydrogen peroxide from hydrogen and oxygen. Catalysis Today. 6/15/
2015;248(0):3-9.

3.         Deguchi
T, Iwamoto M. Catalytic Properties of Surface Sites on Pd Clusters for Direct H₂O₂ Synthesis from H₂ and O₂:
A DFT Study. Journal of Physical Chemistry C. Sep 12
2013;117(36):18540-18548.

4.         Choudhary
VR, Samanta C. Role of chloride or bromide anions and protons for promoting the
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