Conspectus
The rational
design of highly efficient catalysts relies on understanding
their structure–activity relationships and reaction mechanisms
at a molecular level. Such an understanding can be obtained by in
situ monitoring of dynamic reaction processes using surface-sensitive
techniques. Surface-enhanced Raman spectroscopy (SERS) can provide
rich structural information with ultrahigh surface sensitivity, even
down to the single-molecule level, which makes it a promising tool
for the in situ study of catalysis. However, only a few metals (like
Au, Ag, and Cu) with particular nanostructures can generate strong
SERS effects. Thus, it is almost impossible to employ SERS to study
transition metals (like Pt, Pd, Ru, etc.) and other nonmetal materials
that are usually used in catalysis (material limitation). Furthermore,
SERS is also unable to study model single crystals with atomically
flat surface structures or practical nanocatalysts (morphology limitation).
These limitations have significantly hindered the applications of
SERS in catalysis over the past four decades since its discovery,
preventing SERS from becoming a widely used technique in catalysis.
In this Account, we summarize the extensive efforts done by our group
since the 1980s, particularly in the past decade, to overcome the
material and morphology limitations in SERS. Particular attention
has been paid to the work using core–shell nanostructures as
SERS substrates, because they provide high Raman enhancement and are
highly versatile for application on different catalytic materials.
Different SERS methodologies for catalysis developed by our group,
including the “borrowing” strategy, shell-isolated nanoparticle-enhanced
Raman spectroscopy (SHINERS), and SHINERS-satellite strategy, are
discussed in this account, with an emphasis on their principles and
applications. These methodologies have successfully overcome the long-standing
limitations of traditional SERS, enabling in situ tracking of catalysis
at model single-crystal surfaces and practical nanocatalysts that
can hardly be studied by SERS. Using these methodologies, we systematically
studied a series of fundamentally important reactions, such as oxygen
reduction reaction, hydrogen evolution reaction, electrooxidation,
CO oxidation, and selective hydrogenation. As such, direct spectroscopic
evidence of key intermediates that can hardly be detected by other
traditional techniques was obtained. Combined with density functional
theory and other in situ techniques, the reaction mechanisms and structure–activity
relationships of these catalytic reactions were revealed at a molecular
level. Furthermore, the future of SERS in catalysis has also been
proposed in this work, which we believe should be focused on the in
situ dynamic studies at the single-molecule, or even single-atom,
level using techniques with ultrahigh sensitivity or spatial resolution,
for example, single-molecule SERS or tip-enhanced Raman spectroscopy.
In summary, core–shell nanostructure-enhanced Raman spectroscopies
are shown to ...
