The
development of heterogeneous frustrated-Lewis-pair (FLP) catalysts
from homogeneous FLP conception is of great promise in practical applications.
While our recent discovery has shown that all-solid FLPs can be created
on ceria via surface oxygen vacancy regulation (
Zhang
Zhang
Nat. Commun.2017815266),
a sound understanding of the intrinsic property and reactivity of
the solid FLPs is still expected. Here we present a comprehensive
theoretical study on the FLPs (Ce···O) constructed
on CeO2(110) and (100) surfaces by using density functional
theory calculations. We find that the creation of surface oxygen vacancy
can enhance both the acidity of FLP-acid site and the basicity of
FLP-base site. The enhanced acidity and basicity of Lewis sites together
with the elongated distance of Lewis pairs (Ce···O)
contribute to the high activity of solid FLPs. The dissociative activation
of H2 on FLPs experiences a heterolytic pathway (H2 → Hδ+ + Hδ−) with a low activation energy of 0.07 eV on CeO2(110)
and 0.08 eV on CeO2(100). Unlike the phenomenon on stoichiometric
CeO2 surfaces that the dissociated hydride (Hδ−) adsorbed at Ce sites is prone to transfer to more stable O sites,
the hydride on FLPs can be stabilized at Ce sites and thus benefits
the hydrogenation of acetylene via an easier pathway. The rate-determining
barriers of acetylene hydrogenation on FLP-CeO2(110) and
FLP-CeO2(100) are calculated to be 0.58 and 0.88 eV, respectively.
These results could help to understand the nature of solid FLPs and
pave the way for rational design of heterogeneous FLP catalysts.
Dibenzyltoluene (DBT) is a promising liquid organic hydrogen carrier (LOHC) with theoretical 6.2 wt % hydrogen storage capacity which can be coupled with a renewable energy power generation system. In this work, the surface hydroxyl groups and surface oxygen vacancies (SOVs) on alumina were modified by a convenient and environmentally friendly plasma treatment method. Different Pt/Al 2 O 3 catalysts were prepared via impregnation of the treated alumina, and the effects of different surface hydroxyl groups and SOVs on their reactivity for the reversible hydrogenation and dehydrogenation of DBT were investigated. The results show that SOVs increased after H 2 plasma treatment, whereas the surface hydroxyl groups increased and SOVs decreased after O 2 plasma treatment. Both the surface hydroxyl group and SOV can improve Pt metal dispersion. The more interesting observation is that the hydroxyl groups promote hydrogen spillover and the proportion of Pt(0), which not only benefit the catalyst hydrogenation and dehydrogenation activity but also reduce side reactions and increase long-term cycle performance. However, increased SOVs increased the fraction of low coordinated Pt which reduces the long-term cycle performance of the catalyst. As a result, increasing surface hydroxyl groups and appropriately reducing SOVs on Pt/Al 2 O 3 are propitious for improving both reactivity and long-term cycle performance when using DBT as a LOHC.
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