posted on 2024-02-02, 13:03authored byWeiyu Wang, Richard J. Lewis, Bintian Lu, Qiang Wang, Graham J. Hutchings, Jun Xu, Feng Deng
Isomerization
of 1-butene critically influences product distributions
in 1,3-butadiene hydrogenation. However, distinguishing between the
isomerization and hydrogenation pathways is challenging. Here, we
employ parahydrogen-induced polarization (PHIP) NMR spectroscopy to
determine the extent of the isomerization pathway when using Pd–Au
bimetallic nanoparticles synthesized via a colloidal protocol in the
presence or absence of a polyvinylpyrrolidone (PVP) stabilizing ligand
and immobilized on TiO2. Residual additives, in particular,
sulfur, are observed to considerably influence the pairwise hydrogenation
and 1-butene isomerization pathways. PHIP NMR analysis reveals that
the PVP ligand can induce strong polarized signals, likely due to
restricted proton migration, but minimally impact 1-butene isomerization.
In contrast, removing surface sulfur species introduced during catalyst
synthesis profoundly enhances 1-butene isomerization by reducing the
hydrogen concentration at the nanoparticle surface. This work elucidates
how residual species can modulate key reaction pathways such as isomerization
during 1,3-butadiene hydrogenation, with implications for rational
catalyst design.