[Kiriri]

In the decomposition of hydrogen peroxide, transition metals can be used as a catalysts, most notably Ag, Pt and Mg. Are they considered to be heterogeneous? If so, how do they actually work? Because it is a decomposition, they simply line up the chemicals and do nothing else? [which is, as far as my knowledge extends for now, what heterogeneous catalysts does]

[DevaDevil]

is the catalyst a piece of metal, or is it dissolved in molecular (e.g. organnometallic) form?

the answer to that shows you if it is homogeneous or heterogeneous:


HOMOgeneous: same phase as reactants
HETEROgeneous: different phase from reactants.

[Kiriri]

Metal in powder form.

[DevaDevil]

so reason this through:

your catalyst is metallic powder, your reactant is hydrogen peroxide (probably in water)

are these two in the same or in different phases?

[Kiriri]

No, hence it should be a heterogeneous catalyst.

However, I am told that heterogeneous catalysts work by lining up the chemicals so that they collide with each other the correct way. The chemical reaction is a decomposition, so I'm not sure on how this works.

[DevaDevil]

the definition of heterogeneous or homogeneous is not by how they work. It is by phase.


And most heterogeneous catalysts are metal surfaces/particles that adsorb reactants, allow them to get in contact, then desorb products.

In case of a decomposition it adsorbs the sole reactant, interacts with it on either an electronic level (classic example is back-donation of a high work function metal in an antibonding orbital of the reactant, thereby weakening the reactant's internal bond), or on a geometric level (such at Pt(100), a square-planar Pt lattice orientation, facilitating the oxidation of ammonia by lining up the N-H bonds on-top of the Pt atoms), and the desorbs the products.
Still a heterogeneous catalytic reaction.

[Kiriri]

Ah I see, your explanation made sense. Thank you.

By any chance, do you happen to know a book/citable source where I can find an explanation similar to yours? I'm not saying your post isn't credible or anything, but...I do need somewhere "official" the cite from. =<

[DevaDevil]

any book on catalysis will have this.

In my case this is: "Concepts of Modern Catalysis and Kinetics" by I. Chorkendorff and J.W. Niemantsverdriet (Wiley-VCH)

but you should be able to find one in your library. It is better to quote a book you actually have access to.
Else try google books, they often have previews, which may be enough.

In any case this is the definitions in the book:
"In homogeneous catalysis, both the catalyst and the reactants are in the same phase, i.e. all are molecules in the gas phase, or, more commonly, in the liquid phase."
and
"In heterogeneous catalysis, solids catalyze reactions of molecules in gas or solution. As solids are commonly impenetrable, catalytic reactions occur at the surface."

[Kiriri]

Ah, okay. I was searching for the explanation about how heterogeneous catalysts function upon decompositions, but I will assume that is in said book. Thank you.

[Kiriri]

the definition of heterogeneous or homogeneous is not by how they work. It is by phase.


And most heterogeneous catalysts are metal surfaces/particles that adsorb reactants, allow them to get in contact, then desorb products.

In case of a decomposition it adsorbs the sole reactant, interacts with it on either an electronic level (classic example is back-donation of a high work function metal in an antibonding orbital of the reactant, thereby weakening the reactant's internal bond), or on a geometric level (such at Pt(100), a square-planar Pt lattice orientation, facilitating the oxidation of ammonia by lining up the N-H bonds on-top of the Pt atoms), and the desorbs the products.
Still a heterogeneous catalytic reaction.

Just a final, teensy, quick question. If we are still on the same book, which page/chapter/section was that from? Transition Metals?

[DevaDevil]

in the book I mentioned it is in the very first chapter, Introduction to catalysis