[makesyourjrock]

I'm reading a research paper from a University I will be attending in the fall, but am having trouble understanding the distinction between "isolated metal centers" and "metal nanoparticles". I can't find a definition of metal centers that seems to make sense in this context. Any help?

[Corribus]

What is the context?

[makesyourjrock]

"Reaction pathways on isolated metal centers can be very different from those favored on metal nanoparticles." It's a chemical engineering paper on how catalysis via dispersed metals is affected by oxide supports.

[Corribus]

Here's your continuum:

Atom --> Cluster --> Nanoparticle --> Bulk material

The properties of each of these can be quite different, mostly because chemistry happens at the surface of a material.  In the case of an atom, these are typically so reactive that they are rarely "floating about" in the charge zero state - even in gas phase, with the exception of noble gasses.  So a "metal center" will usually be a metal atom, in a formal nonzero oxidation state, bound by some stabilizing ligand or organic/inorganic framework.  An example might be a metal porphyrin.  The type of chemistry that can be occur at, say, the iron bound to a porphyrin, may be quite different from that able to occur at an iron nanoparticle... or a macroscale lump of iron.  Some of this difference may be simply kinetic, but not all of it.

[curiouscat]

There's a ton of papers hypothesising quantum effects on reactivity below a certain critical nanoparticle size.

Dunno how much of that is real.