17
Nanocatalysis
S. Abbet and U. Heiz
17.1
Introduction
The term ‘‘catalysis’’ was introduced in 1836 by Berzelius in order to classify certain types of chemical reactions whose progress is affected by additional substances
which are not part of the reaction products [1]. Since then, a molecular understanding of catalytic processes has been emerging, notably with the introduction of
model catalysts (metal surfaces or metal particles supported on oxide surfaces) [2].
However, most catalysts in use today were discovered by trial and error, by ‘‘shaking and baking’’ metals and ceramics and then seeing how the results affect the
reactions and their products. As we enter the nano-age, another approach is appearing. Indeed, nanotechnology, being defined as the creation of functional materials, devices, and systems through the control of matter at a scale of nanometers,
as well as the exploitation of novel properties and phenomena developed at that
scale [3, 4], the catalysts of the nano-age, called nanocatalysts, are shaped atom-byatom. Different approaches can be used to build nanocatalysts: these are selfassembly, nanolithography or nanoarchitecturing by using the building blocks of
nanotechnology, which are nanocrystals, nanofilms, nanowires, and clusters [5].
Here we define nanocatalysis when two important conditions are fulfilled [6].
First, the valence electrons of the active part of a nanocatalyst are highly confined,
leading to physical and chemical properties non-scalable from the bulk properties. This condition is true for clusters/particles of the nanometer length scale
or smaller. Second, nanocatalysts are designed in a controlled manner. The exploration of materials properties in the non-scalable regime has profound consequences. Atomic clusters, e.g., exhibit unique size-dependent electronic [7, 8],
magnetic [9, 10], and chemical properties [11] that differ from those of bulk materials. In contrast to supported particles of larger size or extended solid surfaces,
small clusters adsorbed at specific sites of a support material change their intrinsic
properties to a large extent, in particular when charging of the cluster occurs.
Nanocatalysts exhibit remarkable quantum size effects and structural fluxionality.
This opens new avenues for atom-by-atom design of nanocatalysts whose chemical activity, specificity, and selectivity can be tuned by controlling the cluster size,
551
Nanocatalysis
S. Abbet and U. Heiz
17.1
Introduction
The term ‘‘catalysis’’ was introduced in 1836 by Berzelius in order to classify certain types of chemical reactions whose progress is affected by additional substances
which are not part of the reaction products [1]. Since then, a molecular understanding of catalytic processes has been emerging, notably with the introduction of
model catalysts (metal surfaces or metal particles supported on oxide surfaces) [2].
However, most catalysts in use today were discovered by trial and error, by ‘‘shaking and baking’’ metals and ceramics and then seeing how the results affect the
reactions and their products. As we enter the nano-age, another approach is appearing. Indeed, nanotechnology, being defined as the creation of functional materials, devices, and systems through the control of matter at a scale of nanometers,
as well as the exploitation of novel properties and phenomena developed at that
scale [3, 4], the catalysts of the nano-age, called nanocatalysts, are shaped atom-byatom. Different approaches can be used to build nanocatalysts: these are selfassembly, nanolithography or nanoarchitecturing by using the building blocks of
nanotechnology, which are nanocrystals, nanofilms, nanowires, and clusters [5].
Here we define nanocatalysis when two important conditions are fulfilled [6].
First, the valence electrons of the active part of a nanocatalyst are highly confined,
leading to physical and chemical properties non-scalable from the bulk properties. This condition is true for clusters/particles of the nanometer length scale
or smaller. Second, nanocatalysts are designed in a controlled manner. The exploration of materials properties in the non-scalable regime has profound consequences. Atomic clusters, e.g., exhibit unique size-dependent electronic [7, 8],
magnetic [9, 10], and chemical properties [11] that differ from those of bulk materials. In contrast to supported particles of larger size or extended solid surfaces,
small clusters adsorbed at specific sites of a support material change their intrinsic
properties to a large extent, in particular when charging of the cluster occurs.
Nanocatalysts exhibit remarkable quantum size effects and structural fluxionality.
This opens new avenues for atom-by-atom design of nanocatalysts whose chemical activity, specificity, and selectivity can be tuned by controlling the cluster size,
551