Why does a catalyst catalyze a reaction ?

[n2mp]

Hello everyone,

I will soon have to change my work subject to work on metal's catalytic
properties and, except the basic notions I got during my chemist formation,
I'm completely incompetent. But a chemist is supposed to be able to work on
any chemistry related subject !... So, here I am...

What I'm looking for is to determine why a metal does catalyze a specific
reaction and not an another one, which can be catalyzed by an another
metal... or even why a given metal at a given oxydation state can catalyze
the reaction while the same metal at a different oxydation state doesn't
catalyze it.
Another formulation of the problem would be :
* on which basis, a reactant "decides" that the adsorbtion site at the
catalyst surface is better than its solvatation shell et fix on it ?
* on which basis, the catalyst will "decide" to adsorb the reactant and
release the previously adsorbed solvent molecules (which are in large
excess) ?
* on which basis, the catalyst will accept that the two reactants it has
adsorbed will react together to form the desired product instead of keeping
them at its surface ?
* and once the product formed at the surface, why will the catalyst let it
go. Finally it has worked without benefits !...

I know that, on the reactants' point of view, the reaction proceeds with
lower activation energy so that it is favoured.

I suspect that the metals used in heterogeneous catalysis acts through
electrons donnor/acceptor effect on chemical bonds. But instead of
suspecting, I'd like to understand and know.

So, if you could provide me some explanation and... a good reference on
those subjects, I would appreciate.

Thanks for your help.
Best regards.

[Uncle Al]

Post by n2mp
Hello everyone,
I will soon have to change my work subject to work on metal's catalytic
properties and, except the basic notions I got during my chemist formation,
I'm completely incompetent. But a chemist is supposed to be able to work on
any chemistry related subject !... So, here I am...
What I'm looking for is to determine why a metal does catalyze a specific
reaction and not an another one, which can be catalyzed by an another
metal... or even why a given metal at a given oxydation state can catalyze
the reaction while the same metal at a different oxydation state doesn't
catalyze it.

Orbital overlap. Hard and soft acids and bases (Grubb's olefin
metathesis catalysts that work in water). Crystallite configuration
(edge, corner, step, dislocation; Au nanoparticles as oxidation
catalysts). Electronic alteration by substrate (CsCO3 doping).
Steric accessibility (traditional Zieglar-Natta catalysts vs. Insite
catalysts on aluminoxane supports).

I'll tell you a secret - it is as much serendipity and hard work
(combinatorics) as quantum mechanics and orbital engineering. You alo
need a test reactor suitable to the job. The best oxidation catalysts
were making only CO2 and water until fast kinetics microreactors were
perfected.

Post by n2mp
* on which basis, a reactant "decides" that the adsorbtion site at the
catalyst surface is better than its solvatation shell et fix on it ?

You go into the literature and look for precedent. You do some
scientific wild-ass guessing. Put out paper loaded with graphs and
tables, hoping to find something interesting before management cuts
its losses.

Post by n2mp
* on which basis, the catalyst will "decide" to adsorb the reactant and
release the previously adsorbed solvent molecules (which are in large
excess) ?
* on which basis, the catalyst will accept that the two reactants it has
adsorbed will react together to form the desired product instead of keeping
them at its surface ?
* and once the product formed at the surface, why will the catalyst let it
go. Finally it has worked without benefits !...

This stuff is exhaustively philosophized upon - "Journal of
Catalysis." If you are hiring techs, remember to ask each candidate if
it is lucky.

Post by n2mp
I know that, on the reactants' point of view, the reaction proceeds with
lower activation energy so that it is favoured.
I suspect that the metals used in heterogeneous catalysis acts through
electrons donnor/acceptor effect on chemical bonds. But instead of
suspecting, I'd like to understand and know.
So, if you could provide me some explanation and... a good reference on
those subjects, I would appreciate.

Google. Library. Everybody pontificates about successful solutions,
nobody knows how to solve the next problem.