Abstract
Heterogeneous catalysis is involved in
the vast majority of industrial chemical
processes performed nowadays, and an
increased understanding of catalytic
reactions is of the utmost relevance
to develop a sustainable and cleaner
technology. In order to make new (or
improved) catalytic solids, an increased
comprehension of the working principles
of heterogeneous catalysis is a prime
requirement. Towards that endeavour,
many rewarding efforts have been made
in the last decades to: (a) determine the
nature and distribution of the catalytically
active sites present on the surface of
the catalyst, (b) unravel the underlying
catalytic mechanisms, and (c) reveal the
close relationship that exists between
the structure (and composition) of the
heterogeneous catalysts and their most
relevant characteristics, which include
activity, selectivity and stability. In this
scientific endeavour, characterization
techniques play a pivotal role and spectroscopic
methods, in particular, have
become the key tool to characterize
catalytic solids. Spectroscopy (from the
Latin spectrum and the Greek skopein
meaning ‘to examine’) comprises a large
group of techniques that, taken either
individually or in several judicious combinations,
can profitably be used to determine
the nature, quantity, structure and environment
of atoms, ions and molecules. Most
spectroscopic methods currently used in
the field of heterogeneous catalysis are
based on the analysis of the interaction of
the catalyst with electromagnetic radiation
ranging from radio and microwaves
through to infrared, visible and ultraviolet
light and finally to X-rays.
However, characterization of the
catalyst (or catalytic precursor) itself
constitutes only a small step towards understanding
catalytic processes. In the end, one
wishes to obtain detailed information on
the catalytic solids under technologically
relevant working conditions, which can
bring about very significant changes to
the catalytically active sites. For this
purpose, in situ spectroscopic cells were
developed that enable the researcher to
investigate the physicochemical changes
taking place in the catalyst while working
at even a high temperature and pressure
of the substrate in a gas or liquid phase.
In situ conveys the meaning of catalyst
characterization at its working place,
in contrast to ex-situ measurements.
Preferably, the in situ characterization
approach should be complemented with
simultaneous measurement of catalytic
activity and selectivity, which can be
accomplished by coupling the in situ
spectroscopic cell with (for instance) a
mass spectrometer or a chromatography
system; the wealth of data thus obtained
is most useful for analysing structure–
performance relationships of the catalysts at
work. And this is how operando (meaning
‘at work’) spectroscopy was born. In
other words, operando spectroscopy can
be regarded as being a very important
class of a much broader group of in situ
catalyst characterization techniques.
Since it provides detailed information
on the surfaces of catalytically active
materials at work, operando surface
spectroscopy seems to be the proper
name for this research field.
Original language | English |
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Pages (from-to) | 2125-2127 |
Number of pages | 3 |
Journal | Physical Chemistry Chemical Physics |
Volume | 14 |
Issue number | 7 |
DOIs | |
Publication status | Published - 2012 |